Rebuilding a Fender Deluxe Reverb
Reissue Amplifier
Featuring MikeyMann Amplification
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01 - Overview
My name is Wayne and this article is about my experience with MikeyMann Amplification turning my Fender Deluxe Reverb Reissue into a reborn, boutique amp. Casting aside the printed circuit board and stock transformers, Mikey breathed new life into this amp with thoughtful improvements to enhance the sound and serviceability.
Mikey’s rebuilt
amp (on left) and Wayne’s stock Deluxe Reverb Reissue (on right)
I’ve written the following account in chronological order so that you can share my sense of discovery of the intricacies of this amp rebuild and the commensurate enhancement of my tube amp electronics knowledge. Keep in mind that while I am a well-informed amateur with a fair amount of book learning, I’m not an amp tech. Since tube amps are a major hobby of mine, I’m always glad to gain new tube amp knowledge and this experience has been a true pleasure in this regard. I hope you enjoy the journey through the rebuilding of this tube amplifier as much as I enjoyed writing it. From one tube ampoholic to another . . . . .
To aid in the navigation of this article, here is a table of contents, which also acts as a link to the various sections of the article. Click on a link to jump to that topic, or read on for the full story.
02 - Introduction
Well, I must admit to an almost morbid fascination with the Deluxe Reverb Reissue (DRRI) amps. I’ve owned three of them over the years. I say “morbid” because each of them has died (primarily related to blown tubes) at some critical point while I’ve been performing. Each time, I’ve sworn them off but like a phoenix rising from the ashes, I’ve come back because the sound of a Deluxe Reverb with its 6V6 power tubes and wonderful reverb hold a special appeal to me. I have found the Fender DRRI as it comes straight from the factory sounds pretty darn good for my playing style and even better with an upgraded speaker, but as with many things, there is plenty of room for improvement.
RCA 6V6
The first time I acquired a DRRI, I purchased it brand new at a yearly special
sale at a local music store. I played
it as my main amp for about 10 months until at a gig, one of the Sovtek 6V6
tubes failed and took out one of the 470-ohm/1-watt screen resistors.
So I took it to my amp tech, Rick, for servicing. It was my first look at the interior and under Rick’s instruction, I learned about the quality of the printed circuit board, the sometimes problematic wiring traces and the difficulty servicing it. As some of you may recall, at a point chronologically after my first DRRI amp, Rick performed a wonderful restoration of my 1971 Fender Princeton Reverb. You can read that tale of transformation on the alt.guitar.amps home page at:
Rebuilding a 1971 Fender Princeton Reverb
Rick patched up my DRRI and I played it for a little while but decided to start looking for better-built amps with a Deluxe Reverb vibe. I sold the DRRI to buy a Tone King Continental head and cab, an amp I still own today.
An opportunity to buy a used DRRI at a good price came along so I bought it. I upgraded to 6V6EH tubes and used the standard speaker. It too gave out at a gig due to a failed tube. I had it fixed but sold it within a couple of months, swearing them off as too unreliable.
Then Tom, a fellow I’d been playing music with for a number of years, left the area and asked if I wanted to buy his DRRI. It was in great shape and was too good a deal to pass up so I bought it and installed a Reverend All-Tone 12” speaker. Guess what, I was playing it about 9 months ago and had the same problem; at a high volume, one of the 6V6EHs failed and took out a screen resistor. My amp tech fixed it up by installing 1K/5W screen resistors and re-soldered some loose grounds and other components on the PCB board.
Vowing to do something about the amp, I got in contact with Mikey (Mike McGuirk) of MikeyMann Amplification. I’d been aware of Mikey’s work on DRRIs through his frequent posting on the newsgroup alt.guitar.amps. He’d done some nice work on his DRRI, gutting his amp and stuffing it with a Hoffman turret “PTP” (Point-To-Point) board and upgraded components. I’d exchanged quite a few bulletin board posts with him on the topic and liked what I’d read. I’d seen examples of his work on the Amplifier Chassis Pics website at:
Of course many of you that are reading this would think I’d have been better off initially buying a Blackface or Silverface Deluxe Reverb. You’re probably right, considering I’m on my third DRRI. But when I first bought the DRRIs, I wasn’t as knowledgeable about tube amps as I am today and with just a little over $300 in the current DRRI, I’ve decided to try something new.
A recent sampling of sold eBay transactions revealed that original Blackface (pre 1968) Deluxe Reverbs had an average selling price of $1255. The downside of purchasing these amps is they often need $250 - $500 in restoration work and tubes and you are still left with an amp that has many 40-year-old components.
Read on and I think you’ll find that buying a used DRRI and getting a MikeyMann Amplification rebuild is a cost effective way to get the Deluxe Reverb sound we love using modern, reliable components that sound great and still have all the panache of a boutique amp. I wish I had done this the first time I bought a DRRI :>)
03
- Rebuild Discussions
Beginning in February, I’ve had long conversations with Mikey about rebuilding my Deluxe Reverb Reissue. We have exchanged lengthy emails with ideas about the rebuild and the conversations have helped clarify my understanding of his concepts as well as his understanding of what I like to hear in an amp. These conversations have also helped educate me about component choices and what they will do to the sound.
As it turns out, Mikey and I have very similar tastes and both like the basic Deluxe Reverb sound. When you talk to Mikey, you’ll soon find out that tweaking an amp to an individual player’s style, their guitar choices and other equipment selections is the key to getting the best sound for the player.
The circuit he uses as the starting point for his modifications is (not surprisingly) the one used in Deluxe Reverbs, which is called the AB763. It is used in a variety of Blackface Fender amps including the Deluxe Reverb, Super Reverb, Vibroverb, Virbrolux, Twin Reverb, etc. This means if you have a Blackface Fender reissue amp, chances are the AB763 circuit is used. Of course, there are variations to the circuit depending on the number and type of power tubes in a particular reissue amp.
Often, when I want to find detailed Fender amp information,
I go to the Fender Amp Field Guide. There's a host of great information
about all of the vintage Fender amps, plus, you can find copies of the chassis
layouts and schematics, which is where the AB763 diagrams on this page came
from. Check it out.
Deluxe Reverb
AB763 chassis layout (click picture for full size, external link)
Deluxe Reverb AB763 schematic (click picture for full size, external link)
Although Mikey has previously made a variety of
different circuit boards, he decided to specialize in rebuilding the Fender
reissues, specifically the Blackface and Tweed Bassman amps, and the reissue
stand-alone reverb unit. Mikey says he may offer other circuits in the
future and is considering additional performance upgrades for popular
Fender amps not currently in the reissue line such as the Blues Jr., Pro Jr.,
Blues Deluxe, Blues DeVille, Hot Rod Deluxe, Hot Rod DeVille, etc.
He got his start building amplifiers by using Hoffman Board Kits,
which are no longer manufactured by Doug.
Mikey has been a long-time fan of Doug Hoffman’s circuit designs and
continues to get parts from the Hoffman Amplifiers website. In fact, some Hoffman parts have found their
way into this project. You can check
out the parts for sale and access other excellent tube amp information at:
In one of many emails I received from Mikey, he offered these comments regarding the people that inspired and informed him during his quest to build tube amps:
"I have to say, that I have a lot of respect for Doug.
I learned an incredible amount about amp building from his website, which has a
ton of information that he offers FREE of charge. He absolutely has one
of, if not the best, amp building forums around. There aren't too many
experts out there that offer their knowledge to others free of charge.
Doug Hoffman and Randall Aiken are two that come to the top of my
mind. I've learned a lot from both of them and I hope to be able to
"pass the torch" by offering the knowledge that I've gained, and hope
to gain, with others as well."
I can certainly relate to Mikey's
comments about Randall Aiken. I purchased one of the first Aiken Invader
amps in the early summer of 2001 and have been gigging with it ever
since. It’s a wonderful amp.
Randall's website is chock-full of technical information. I
recommend checking it out at:
During discussions about
rebuilding my amp, I had the opportunity to consider and
select some optional mods to Mikey’s “stock” rebuild. For example, I chose the option for a Triode/Pentode
switch for lower volume situations.
I learned that Mikey likes to modify the negative feedback loop from the standard AB763 circuit because he has found a sweet spot for this amp to increase gain and harmonics.
He suggested modifying the normal channel for more midrange, overdrive and a more Marshallesque tone. On his personal amp, he added a pot in place of the extension speaker jack to allow full-range control of the midrange. While I still want to keep the extension speaker jack, the plan is to test different midrange settings on his amp with my guitars to find the optimum setting, which will be set at a fixed value by placement of a properly-speced resistor in the tone circuit of the Normal channel.
Internally, in addition to a new circuit and filter cap boards, Mikey said I could select the option to add bias points on the back of the chassis with adjustments made via the bias pot accessed through the bottom of the chassis. Normally, the bias pot is located on the main circuit board. The bias can still be adjusted without the bias test points but the chassis has to be removed to get the measurements, or you can use a bias probe (purchased separately) in the power tube sockets. Although it costs more, I chose the option with the external bias test points, which will allow me to change output tubes without taking the amp to a tech.
There will be 1K/5W screen resistors on the 6V6 tubes to prevent the kind of failures I experienced on all three of my DRRIs.
Mikey suggested a phase inverter (PI) mod to limit the farting out of the speaker at high volumes. Lowering the PI’s cap value does this. Mikey has refined the sound of his circuits by making subtle changes here and there rather than a couple of major changes. For example, to balance the lower cap value in the PI, which raises the low frequency limit but still keeps it below what the speaker can reproduce, Mikey increases the PI coupling cap to lower the frequencies going to the PI to compensate by allowing a bit more midrange / fullness through.
He suggested a mod to run the Normal channel through the tremolo and reverb circuits, putting both channels in phase. This will let me use an A/B/Y pedal to run the channels separately; with the Normal channel having a bit more gain and midrange, and the Vibrato channel retaining the cleaner Deluxe Reverb sound. With both channels in phase, I will also be able to run them together for even more sonic goodness.
Mikey’s circuit uses the pulsating bias tremolo circuit of the 63' Vibroverb and not the optoisolator type that is used on most Blackface Fenders. This circuit alters the bias of the power tubes instead of an on/off optoisolator.
He’s also going to adjust the reverb circuit by using a 100K audio pot in place of the 100K linear pot to give more fine control so the reverb won’t jump too quickly from subtle to surf.
There are other options to consider when getting a rebuild done by Mikey. He is a BIG fan of Mercury Magnetics iron. These high-quality parts apparently have a great effect on the tone of the amp and Mikey insists on using Mercury Magnetics output transformers and chokes in his rebuilds. Mercury iron can also be used for the reverb transformer and power transformer. I initially chose the option to add the reverb transformer, but as you’ll see in a later section, I’m convinced the Mercury power transformer is a worthwhile upgrade.
I certainly learned a lot in my email and phone conversations with Mikey. I decided I wanted to document this rebuild so in addition to saving all the emails, I asked him for digital photos of each step of the building process. He agreed and what started as my personal record keeping has ended up as this full-blown website.
When all is said and done, I’ll have boutique amp quality for quite a bit less than the cost of a new boutique amp and this one will be personally tweaked by Mikey to my sonic preferences. Plus, it'll be like a wolf in sheep's clothing, housed inside the Fender chassis and cabinet. Sounds good to me!
04 - Visiting MikeyMann Amplification
In July, I traveled to Baltimore, Maryland (USA) with my DRRI to meet with Mikey. I arrived in the early afternoon and took copious notes to share the experience with you. Here’s how we spent the day, including a lot more information that I learned about rebuilding this DRRI amplifier.
Once I arrived, I carried my two favorite Hamer guitars and my DRRI amp in from the car and met Mikey for the first time, and his two cats. One cat is unabashedly friendly and the other one is quite reserved and timid. After getting the animal familiarities out of the way, Mikey and I took some time to get to know each other.
Mike McGuirk (aka Mikey) in his shop
I asked him about his business name, MikeyMann
Amplification. He shared with me that
once when visiting his oldest niece,
she spontaneously said, " Hey, Uncle Mikey Man!" Then, whenever
she saw him, she’d call him “Uncle Mikey Man”. This term of endearment
has been used by all of his nieces over the years, which is how the name
MikeyMann Amplification came to be.
We then talked about our love of tube amplifiers, guitars and the musicians that have influenced us. We shared war stories of bands we had played in over the years and most importantly, discussed the amps we’ve played in the past and the amps we own today. We also discussed the state-of-the-art in modern tube amp construction and spoke of the knowledge we’ve both gained by participating in the AGA newsgroup (alt.guitar.amps).
We also discussed a host of Internet sites, tube amp books and interactions with other musicians that have helped us out. I’ve learned a lot from The Gear Page website at:
Mikey highly recommends The ToneQuest Report for detailed
reviews on amps, guitars and other musicians’ toys. He says,
“It's my favorite publication, even above Guitar
Player. I look
forward to receiving it each month, and I devour it for its information and
knowledge. I save all of my issues so
that I can refer back to specific articles and information. It's also cool to read what some of the
great players are using, how they have their rigs set up, etc.”
I like it too and buy it off the newsstand at music stores. You can find out more about it here:
Mikey is a joy to talk to about these topics and we spent the first couple of hours in animated conversation. Mikey took the time to talk about his vision of rebuilding reissue amps with modern construction techniques using the best of modern components. His vision is to build amps for working musicians, pros, semi-pros and serious players who want the best possible tone and top-notch reliability. He makes a compelling case for using the cabinet, chassis and some of the components of the Fender reissue series instead of buying an old Blackface or
Silverface amp and only upgrading some of the components, leaving 30 – 40 year old components in place that could fail at an inopportune time.
I thought you might enjoy reading Mikey’s vision as stated in an email he wrote me:
“Lots of players want/need great tone, but
can't afford the thousands it usually takes to get a handmade or boutique amp,
or even certain vintage amps whose costs have skyrocketed over the last few
years. My goal is to offer great tone
and make it more affordable to a greater number of players. Also, many gigging musicians and pros don't
want to take their vintage gear on the road for fear that it will get stolen or
destroyed. By rebuilding reissue amps
like the Deluxe Reverb, they get the great vintage looks and tone but don't
have to worry about a priceless vintage amp getting stolen or damaged. If so, they can simply get another one!”
“My personal feeling is that if someone does buy
a 40 year old vintage amp, chances are it will have new electrolytics, probably
some new coupling and tone caps, new resistors (at least plate resistors),
maybe a new output transformer, new tubes, maybe a new speaker, maybe even a
new power transformer. So, does the
player "really" have a vintage amp? I say that they have a
vintage chassis, vintage cab but not a "vintage amp". Once you start replacing a bunch of stuff on
a 40-year-old amp, it ceases to be a "vintage amp", in my humble
opinion. You still have a vintage
chassis and cab, but with a bunch of new parts. So, you're paying all that money for a "vintage amp",
but you're not totally getting a vintage amp, just a vintage chassis with a
bunch of new parts. Where's the logic
in that?”
After our very pleasant and wide-ranging conversation, it was time to delve into the details of the amp rebuild. What follows is a section-by-section account of what is planned.
05 - Design Details
The stock DRRI uses printed circuit boards with smaller components and the pots and jacks are mounted to the green PCB. Mikey’s amp uses turret board construction and the pots and jacks are mounted to the chassis and hand wired. Look at the differences in the capacitors, resistors and wiring (instead of ribbon cables). A picture is worth a thousand words and this photo shows the dramatic differences between the two amplifiers.
Mikey’s rebuilt amp (top) and Wayne’s stock Deluxe Reverb Reissue (bottom)
Mikey and I went into the shop and started talking in detail about all of the planned changes to my amp. He took the time to patiently answer all of my questions as we went through each section. I really learned a lot during this session.
Starting with the main board, I learned that Mikey uses a 1/8” G10 board and turrets. Of course, I’ve seen turret board construction in other amps but I didn’t really understand how it is done. Mikey showed me how a large board is measured and cut to size. Then a circuit template (plastic) and a drilling jig (metal) is laid on the G10 board. The template indicates which holes need to be drilled and the jig is used to guide the drill bit as it cuts the board. Once all the holes are drilled, metal turrets are placed through the holes and a special tool is used on the drill press to flare the turrets in the board so they grip firmly. This is a time-consuming process but it makes for very solid construction.
Mikey talked about his existing circuit board template used on the amp shown in the above picture but he has since refined the circuit and construction techniques so he will be using a modified template for my amp. As we worked through the sections of the amp, he took the time to show me how the existing circuit in his personal rebuild would be modified for my build. Hey, I’m getting all the latest whiz-bang improvements!
One of the improvements is the use of 18-gauge buss wire,
wrapped in a Teflon shield for the power rail and ground rail on the
board. This will help insulate power supply noise from the signal
wires that are in close proximity.
Here’s what Mikey has to say about the use of Teflon shielding.
“Teflon is one of the best insulators available and
by using Teflon as a shield on the power and ground rails adds additional
protection for any hands that happen to be in the chassis! High voltage,
bare wire, and hands don't mix too well!”
Mikey will be using the optional Mercury Magnetics iron in
my amp for the output and reverb transformers and the choke. (Note:
A few days before picking up my amp, a decision was made to talk to
Mercury about removing the DRRI power transformer and replacing it with a
Mercury Magnetics power transformer.
This makes for a good story, which you can read in a later section.)
Mercury Magnetics is highly regarded and they’ve taken the time to reverse engineer the best sounding transformers. Mikey explained they use interleaved windings, which the Fender transformers in my stock DRRI don’t have. If nothing else, Mikey strongly recommends using the Mercury output transformer because it adds so much more tone for a few more dollars. You can find out more about this company by following this link:
Here’s a photo that shows the DRRI iron compared to the
Mercury Magnetics iron.
Stock DRRI chassis
(top) and replacement Mercury iron (bottom)
The choke and the output transformers from Mercury Magnetics are significantly larger than the stock iron. I wasn’t clear on the purpose of the choke so Mikey explained that it is an inductor, which means it opposes changes in current. As current decreases, it lets more through and vice versa. The inductor smoothes the current whereas a resistor doesn’t offer any flexibility in how much current it lets through.
On the back of the DRRI, there is an unused switch that was used to change the polarity of the AC coming into the amp on the old Blackface Deluxe Reverbs. Since all modern amps use a grounded AC connection, this switch isn’t needed. Fender put this switch in just to make the back of the amp look like an original.
On my amp, this SPST (single pole, single throw) switch is replaced with a DPDT (double pole, double throw) switch for the Triode/Pentode mod. This changes how the 6V6 tubes operate. If someone chooses a different mod like turning the negative feedback loop of and on, the SPST switch can be reused.
6V6s are pentode beam power tubes. These do the “heavy-lifting” power amplification in the amp. There are five main parts inside a pentode tube, which are the cathode, grid, screen grid, suppressor grid and plate. The heater in the tube is powered by filament wiring coming from the power supply. These heat up the cathode, which starts shedding electrons causing DC current to flow through the tube. The very low signal from the guitar goes into the preamp section of the amp and the preamp tubes do the initial signal amplification and tone shaping. This signal comes out of the preamp section and is introduced into the power tubes at the grid. Here’s a scan from the RCA Receiving Tube Manual.
Pentode circuit showing the parts of the tube (inside the circle) and the signal path
The Deluxe Reverb uses a method called “fixed bias” by making the grid negative with respect to the cathode when no signal is present on the grid. Depending on the amount of negative DC voltage on the grid, the tube will let more or less current pass on through. The bias pot on the bottom of the Deluxe Reverb chassis is what is used to make this adjustment.
Since the bias voltage is negative, more negative bias voltage to the grid restricts the electrons coming off the cathode, which restricts the current flowing to the plate. Less negative bias voltage to the grid allows more electrons to pass to the plate. With less current going to the plate, the amp is considered to be biased “cold” and with more current it is biased “hot”.
The screen grid helps keep the electron flow stable by reducing oscillations. The suppressor grid deflects secondary emissions back to the plate, which results in more power. The plate receives the electrons coming from the cathode. As current flows from the cathode to the plate, the varying preamp signal on the grid is amplified big-time and then it flows into the output transformer, which drives the speaker.
Mikey explained that when the Triode/Pentode switch is thrown, the screen grid is tied directly to the plates of the tubes, essentially eliminating the suppressor grid. This reduces the power of the amp and changes its tone and feel. The volume is lower, the tone is smoother and darker and the breakup happens sooner. It’s a nice thing to have for lower volume situations, for bright guitars and probably for players who like jazz. The nice thing about this mod is that when the switch is set for Pentode, the response is exactly the same as a Blackface Deluxe Reverb.
06 - More Details
In the last section I talked about 6V6 tubes for power amplification. I thought you’d enjoy seeing this photo of two 6V6 tubes; the type of power tube used in Deluxe Reverb amps.
A matched pair of NOS, NIB Visseaux 6V6 power tubes from Lord Valve
These particular 6V6’s are some of
the best ones ever manufactured. They
were made in 1951 for the French military.
NOS means they were sold as New Old Stock (never used). They are also NIB, which means they are
essentially New In the Box. These are
beautiful sounding tubes that compare favorably with the famous RCA blackplate
6V6’s. For new tube manufacturers of
6V6 tubes, I like Electro-Harmonix and JJ Electronic. I usually purchase
my tubes from Lord Valve of NBS Electronics in Denver, Colorado (USA).
You can get on his detailed tube mailing list for the latest information and
pricing:
One of the things I don’t like having to do is to take my amp to a tech for biasing when changing power tubes. The DRRI has a bias adjustment on the bottom of the chassis, which is a good quality CTS 10K bias pot so Mikey reuses this part in the rebuild. As I mentioned, Mikey is adding an optional mod to my amp so that I can bias it myself without opening up the amp and exposing myself to lethal charges or having to buy an external bias probe. Mikey solves this by adding three test points on the back of the chassis so I can set my own bias with a voltmeter using the cathode resistor method.
The way this works is a 1-ohm 1% resistor is placed between ground and pin 8 on the power tubes. When you plug a voltmeter into the test jacks, it’ll measure the voltage drop across the resistor. When I pick up my amp from Mikey, we’ll play with the bias on the tubes to find the spot that sounds best for me and is within the operating parameters of the 6V6 tubes. When it is time to replace my power tubes, I’ll buy a matched pair and then re-bias the amp to these same settings. This is really a nice way to make the amp user-friendly.
Mikey and I had been knee-deep-in-the-hoopla for 3.5 hours and we decided it was time for a break. We went to the kitchen and got a couple of Cokes, ice and glasses and sat outside to relax a bit. I continued to ask Mikey about the technical details of the rebuild and about tube amp electronics.
Mikey told of his time in the military and his assignment in Alaska where he played concerts with his band. At one big concert, he played to a huge crowd sharing the bill with Little Feat, Tower of Power, W.P. Brennan from Australia and 14 other local bands. It was like a mini Woodstock and it sure sounds like it was a lot of fun. After this brief respite, we returned to the shop and picked up where we’d left off.
Next up was a discussion of the typical negative feedback loop (NFB) used in the Deluxe Reverb and the tweaking Mikey has done to get the best response out of it. I learned that a global NFB loop is created by taking the signal from the output transformer at the positive terminal of the speaker jack and sending it back through a resistor to the phase inverter, which is at point earlier in the circuit before the power tubes. It is called negative feedback because this output signal is 180 degrees out of phase with the input signal.
Mikey experimented for a long time to find just the right resistor so that it wouldn’t mess with the clean sounds except making them a bit fatter with more harmonics. It also helps the tone when the amp is pushed hard, giving the amp more gain and girth. I was to experience this later when we started trying out the amps. Here’s what Mikey had to say about his modification to the NFB loop.
“This acts like a fixed Presence/Resonance control. Presence usually only allows the higher frequencies to pass through without going through the NFB circuit, and Resonance usually lets the lower frequencies through without going through NFB. The resistor mod that I'm using works with all of the frequencies, it doesn't only pass either high or low frequencies. It restricts the amount of signal that goes through the NFB circuit so that it leaves a portion of all of the frequencies to be reproduced naturally, without NFB. NFB reduces distortion and makes for a cleaner tone. Since a portion of the tones aren't going through the NFB circuit, they're reproduced fully, with more harmonics and Phatness!”
Regarding the phase inverter (PI), Mikey does some mods to this circuit too. This includes putting in a very high-quality coupling cap leading to the PI because all of the signal from the entire preamp section, reverb and tremolo pass through it on the way to the phase inverter. The PI caps themselves are also of high-quality. Here’s what Mikey has to say about his changes to the phase inverter circuit.
“The PI caps were modified to prevent the "farting" when playing at high volume. The PI coupling cap was actually raised a bit, to compensate a little for the PI cap change, and to let some more midrange/fullness through from the preamp circuit to the PI. My philosophy is that it's better to make several smaller changes/mods throughout the entire circuit than to just make one large/huge change and throw everything else off. Where I make one change, I usually try to make another small compensating change somewhere else in the circuit.”
Another enhancement Mikey makes from the stock DRRI is that he removes the Fender pots and jacks attached to the PCB and replaces them with new pots and jacks; wiring them directly to the appropriate parts of the circuit. He uses CTS and Alpha pots and Switchcraft jacks.
CTS pot (left),
Switchcraft jacks, Alpha pot (right)
The Alpha pots fit the existing holes but in order to use CTS pots, the holes must be enlarged. To do this, Mikey uses UniBits (step drill bits). His design calls for using shoulder washers to insulate the input jacks from the chassis to help keep the amp quiet. The input jack holes have to be enlarged to 1/2“ to accommodate the insulating shoulder washers.
Mikey puts the Normal channel in phase with the Vibrato channel. If this isn’t done and you try to play the amp when using both channels simultaneously, the sound is really puny since they are out of phase. This mod also has the advantage of routing the Normal channel through the tremolo and reverb circuits, which isn’t normally available on a Deluxe Reverb. The Normal channel is also modified to give Marshallesque tone and gain. He explained his goal is to add an extra midrange emphasis and allow the circuit to overdrive sooner.
During our conversation, I became curious about the use of different types of capacitors and how they are used to modify tone. Mikey explained to me how a capacitor works and showed me examples of “film and foil” caps and “metallized” caps. He had a couple of them disassembled and he used them to help me understand how caps are constructed. I now know that film and foil caps use two strips of film and two strips of foil, with a set of film and foil strips creating one “layer”. Metallized caps have two strips, each with an aluminum conductor atomized and vapor deposited on dielectric film. In both cases, the two layers are rolled up together so there is an anode conductor and a cathode conductor separated by a layer of film.
Two different methods of construction are evident in these two types of capacitors
Film and foil caps are much bigger than metallized caps. You can see this in the picture above. Both caps have the same .03uF/600V rating, but the polypropylene and foil cap is much larger/rounder than the metallized polypropylene cap on the right. On the left, the metal foil is less shiny and crinkled looking when unraveled. On the right, the metal looks very shiny and smooth since the metal was sprayed directly on to the dielectric (the polypropylene film).
The way a capacitor works is when power is applied from the positive and negative wires from the power supply, it becomes charged (one of the layers becomes positive and the other negative). Even with the power supply disconnected, the capacitor will continue to hold a charge. How much of a charge it can hold is measured in Farads (F). Another measure is the voltage rating, which tells you how much DC current the capacitor will block. In the above photo, the capacitors are rated at .03 microfarads and 600 volts.
While capacitors will block DC current, they will allow AC current to “flow” through. In actuality, capacitors cycle through charges and discharges somewhat like a very fast, rechargeable battery, which appears to be a flow of AC current. Interestingly, this cycling happens to let high frequencies pass through more easily than low frequencies. This means that capacitors can be used to shape tone in addition to passing an AC signal from one circuit to another without letting any DC current to get through.
There are many types of materials used for cap construction but polypropylene and polyester (foil or metallized) are the most common. Other examples of capacitor construction are paper/oil, polystyrene, polycarbonate, mica and ceramic. Mikey had this to offer on his choice of capacitors (note the preparation he did for my visit based on our voice and email correspondence).
“I
generally prefer polyester caps overall as they give off a "warmer"
tone/more midrange, which is especially nice in a bright Fender circuit. But I changed the caps in my amp for your
demo and used polypropylene Orange Drops for the PI caps and PI coupling
cap. I also used them in the normal
channel tone stack and a couple of other places since you like a brighter
tone. Polypropylene gives off more
highs and more lows to my ears. Those
were polypropylene/foil caps, 716P's.
Polyester, either metallized or foil, tends to give more mids and upper
mids.”
Mikey explained a technique he will to use for the building of my amp. He calls it “Cap Stacking”, which is the use of a combination of caps of different types wired together to get the tone and grit characteristics to best fit his redesigned circuit and my particular tone preferences. I really enjoyed this part of the discussion and learned a lot I didn’t know about caps. As you can see, there’s a lot of attention to detail that goes into the design of Mikey’s amps.
There is an option Mikey uses that I did not select. On his amp, Mikey added a pot on the back of the chassis to the Normal channel to have variable control of the midrange EQ. This lets you dial-in just the right amount of mids for your particular guitar and for the sound you are going for. Mikey installed this extra pot in place of the extension speaker jack. Since I sometimes like to use a Celestion Alnico Blue extension speaker, Mikey said that when we try out his amp, I can find the sweet spot of the mids on his amp that best suits my taste preference. He’ll measure the resistance of the pot at that setting and just build it into the circuit of the Normal channel, leaving the extension speaker jack available.
The tremolo circuit is different from the stock DRRI circuit. His tremolo circuit uses the bias to pulsate the power tubes to generate a smooth tremolo effect rather than the on/off type found in the DRRI, which uses an optoisolator. He also slows down the tremolo circuit and raises the intensity a bit to get the most pleasing sound.
The reverb circuit is also significantly different from stock in several ways. The DRRI uses lower quality, PCB housed RCA jacks, which Mikey replaces with heavy-duty RCA female jacks affixed directly to the chassis. To do this, another hole has to be drilled in the chassis but the quality is worth it. I chose the option to use a high-quality Mercury reverb transformer. As anyone that uses a Fender amp with reverb knows, if you turn the reverb knob up past 2, it gets pretty boingy and surf-like. This is because of the use of a linear pot on the stock DRRI. Mikey uses an audio pot for this application so the user can have finer control of the reverb by allowing more incremental changes. Here’s Mikey’s explanation to me of the differences between linear and audio pots.
“Linear
pots are the same price as audio pots.
It's in the way that the pots function that makes the difference. The resistance of a linear pot is, well,
linear! It's in equal increments. For
example, if you have a 100K linear pot, and you turn the knob to the halfway
point, the resistance will be 50K. An
audio pot functions differently, but it functions closer to the way that our
ears hear. For the same 100K pot, the
halfway point may only represent about 20% of the total resistance, or about
20K.”
“As the
knob rotates, the resistance goes up more, then finally arrives at the same
100K total resistance value. But, it's
that first half of the audio pot that gives us finer control, to get those
"in-between" values, and again, human ears "hear" in audio
fashion, not linear. That's one of the
reasons that on the Fender reverbs that use linear pots, it sounds like it's
"all on" even when the knob is only on 2 or 3. An audio pot would be halfway up
approximately to get that same level.”
“On some
of the less expensive amps, some makers use linear pots on their volume
controls so the customer thinks the amp is "loud". Imagine being in a store and trying out an
amp, turning the volume up to 2 and blasting out the store. The customer would think that this was one
loud amp, but the linear pot makes the ears think that the amp is loud when
it's just giving more volume upfront due to the nature of the linear pot. With an audio pot, the volume control may
have to be up around halfway to get the same perceived volume.”
We finally finished going through the various parts of the amp and all of my questions had been answered. At this point, Mikey and I had been talking for about 5.5 hours and we hadn’t played a note yet. It was time to change that!
07 - Comparing the amps
The two guitars that I brought with me were a Hamer Duotone Custom and a Hamer Artist Custom. The Hamer Duotone has a Seymour Duncan ’59 humbucker in the neck and a RIO BBQ humbucker in the bridge. The Hamer Artist Custom (my favorite guitar) has a Seymour Duncan PhatCat P-90 in the neck and a Seymour Duncan Seth Lover humbucker in the bridge.
My favorite guitar – a 1996 Hamer Artist Custom
I play a lot of different styles of music including rock, blues, country, folk and reggae. I’ve been playing guitar since 1966 and a lot of that time has included acoustic guitar, which has influenced my electric guitar technique. About 60% of the time, I finger pick with all 5 fingers of my right hand, using a modified Travis picking technique of keeping the bass going with my thumb while dropping harmonies and melody in with my other fingers.
Because of the influence of my acoustic playing, I tend to like tube amp tones that are bright and just hovering at the edge of breakup. I’ve always felt the Deluxe Reverb enhances my style of playing. I love to let open strings ring out and I like to use reverb to let the sound swirl.
I also like to get down and dirty (who doesn’t?) and enjoy playing singing leads with an edge. I also like crunchy power cords, ala AC/DC. Could one amp handle this range of styles? To get this variety out of my DRRI, I have to use a Voodoo Labs Sparkle Drive to push the amp into singing sustain.
The first thing Mikey wanted to hear was my playing style and the sounds I typically get out of my DRRI. I grabbed my Hamer Artist Custom, switched on my favorite pickup (the P-90) and started playing a variety of songs and leads. As you’d expect, even when using the humbucker on this guitar, I couldn’t coach my amp into singing sustain. Switching to the Hamer Artist Duotone and its humbuckers got me closer to this but it still wasn’t enough to push it over the top. One thing I’ve always liked about the DRRI though is the way it can give me enough brightness to overcome the darker tendencies of my P-90 and humbucker pickups. I always like some top end zing and enough crispness to let me drop into pseudo-acoustic sounds by turning down my guitar volume.
Next up was Mikey’s rebuilt amp. Using the P-90 pickup of the Artist Custom, I plugged into the Vibrato channel using the exact same settings as my DRRI. I immediately liked the smooth, complex tones that came out of the amp, which has a Weber C12N speaker. In my experience, if I don’t like a tube amp sound within the first 15 seconds, it is unlikely that I’ll be able to dial it in. Well, I’m here to say that I liked it right away!
When I plugged into the Normal channel, it was noticeably louder and had more grit than the Vibrato channel. It was also brighter, which I liked. Using the Seth Lover humbucker, the Normal channel crunches like mad and gives a very exciting rock and roll sound. Brilliant. I liked this channel even more than the Vibrato channel. This isn’t your father’s Deluxe Reverb.
The humbuckers on the Hamer Duotone have even more output and when these push the Normal channel on Mikey’s amp, watch out! Single note leads could be coaxed into singing, controllable sustain with just the right combination of overdrive and clarity, much like the beautiful lead tones that Duane Allman used. With the guitar volume at 10 and the amp volume of the Normal channel at 6, it was pure rock and roll heaven. Mikey and I were both grinning from ear-to-ear.
Mikey brought out a StarTouch A/B/Y foot pedal so that I could hear how both channels sounded together. This is a very well made and transparent pedal. I really liked it. You can check it out here:
With both channels in phase, it was easy to have the best of both worlds. I really enjoyed being able to dial-in cleans from the Vibrato channel and crunch from the Normal channel. It also made it easy to switch from one channel to the other to hear the sonic differences.
I also had a chance to try the Triode/Pentode switch on both channels. This has the intended effect of dropping the gain and making the amp darker. It’ll be nice for some applications where I don’t want to be as loud, but in general, I much prefer the Pentode setting.
Then we tried the tremolo circuit. Wow. What a difference between it and my DRRI. The tremolo has a slow, subtle, hypnotic effect that just seemed to breath. It added a lush, 3D sound similar to a UniVibe. It’s like having an effects pedal built into the amp that doesn’t mess with the pure tube tone. I rarely use tremolo but I can see myself using this circuit. Once again, I liked it right away.
Next, we plugged Mikey’s amp into the speaker in my DRRI cab. My DRRI has a Reverend All Tone 1250 (12” 50-watt) speaker that has always seemed just right for my amp. I'm not alone in my assessment of this speaker. On the newsgroups, it isn't uncommon to read that other players have found this speaker to be the ONE for a Deluxe Reverb.
I have a Celestion Alnico Blue
speaker but I prefer the Reverend All-Tone 1250 if I'm using a single 12"
speaker with this particular amp. If
you'd like some more info on this fine, reasonably priced speaker, check out
the Reverend website at:
Reverend Guitars and the All-Tone 1250 speaker
When we plugged in and fired up the Vibrato channel, the sound was darker than when played through Mikey’s speaker. It is amazing what a difference a speaker can make!
Of note, Mikey plays a customized G&L ASAT (Telecaster style) guitar, which is bright to start with. With his guitar and brighter speaker, it's not surprising that his amp played with my guitars and through my speaker was darker sounding. Since I like a bright Vibrato channel, Mikey said he’d further modify this part of the circuit for my playing style and equipment.
I would like to add that the Vibrato channel still sounded great. When I turned up the volume on the guitar using the P-90 pickup and plucked a single note, the sound from the amp swelled and receded, swelled and receded. I always view this as a critical sign of a well-designed amp. Tube amps should breath like this. It adds so much to the enjoyment of the player and the listener. This amp has it in spades.
Switching over to the Normal channel with my speaker produced a wonderful, exciting sound that was lacking nothing. Since the Normal channel on Mikey’s amp was brighter than the Vibrato channel, my darker speaker merely complimented it. Once again, I cranked up the guitar volume, switched to humbuckers and had us both grinning from ear-to-ear once again. I loved the way the Normal channel sounded through my speaker and I told Mikey I thought he’d hit a home run with this channel.
By now, we’d been at this for 6.5 hours, it was 7:30 at night and suddenly we both started to think PIZZA. We called up the local Pizza Hut and both ordered our favorite toppings. While we waited, we grabbed another couple cans of Coke and ice and sat out in the warm, night air.
After a bit, Mikey’s daughter showed up and I got to meet and chat with her for a bit. It was nice to meet a member of his family and see this side of his personality. I got to interact a bit more with the friendly cat when the doorbell rang and the pizza arrived.
Pizza
We sat outside as the sky darkened, enjoying the pizza and our further tone conversations. I was really excited by what I had just heard and Mikey was charged up by the enjoyment he could see in me. We talked for quite a while about the subtleties of tone and the qualities of the Normal and Vibrato channel through my speaker. Mikey spoke of refinements to the Vibrato channel that he could make so that it would better match my speaker, my guitars and my style.
Mikey said this type of tweaking to a player’s preference is at the core of his design approach. He pointed out that walking into a store and buying an amp, even an expensive boutique amp, doesn’t guarantee a match with a player’s guitar and style. He said he has chosen the AB763 circuit used in the Deluxe Reverb (and many other Fender amps) as a good starting point in trying to give a player customized solutions. He was proving it by me!
Mikey had a couple more things he wanted me to try, so after this relaxing pause we returned to the shop and fired up his amp into my speaker.
This time, Mikey had me play through the Normal channel while he adjusted the midrange pot on the back of his chassis. Using both guitars and all pickups, I played a variety of licks and songs, listening for the subtle and not so subtle changes he was able to elicit with this control. It became apparent that my favorite setting was right between 11:30 and 12:00 on the pot. Mikey will build a resistor into the circuit of the Normal channel of my amp to give me my preferred mids setting.
We went back to the Vibrato channel and listened again, particularly to the volume and the brightness. I told Mikey that I liked the smooth, 3D sound of the channel but would enjoy a volume level a bit closer to the Normal channel as well as a brighter sound. Of course, the Normal channel should have more gain than the Vibrato channel so that when I’m playing, I can step on the A/B/Y box and kick in with a lead sound. To get the brightness but retain the smoothness, Mikey referred again to the use of his Cap Stacking method and how he could use this to get what I was after. He made some notes and I could see that he was really interested in redesigning this part of the circuit.
Mikey suggested we try swapping some 12AX7 tubes in various stages of the amp to determine which tubes would most enhance what I was looking for. We primarily focused on the V2 position, which originally had a JJ in it. We had some nice tubes to try including the new Groove Tubes 12AX7-M (Mullard copy), a JJ, an EH and an old Telefunken. The Telefunken tube may have been at the end of its useful life. It was the noisiest of the tubes and was just so-so in terms of tone.
The GT tube was darker but added a nice swirly, lush tone. It was also the nicest feeling tube from my perspective, giving me the sense that my strings were rubber bands that I could really use to change the dynamics. The JJ was pretty quiet but was darker than the tube that I thought sounded the best, which was the Electro-Harmonix. This tube was the brightest of the bunch, had a low noise level and produced nice, swirly harmonics. When switching to the Normal channel, this was the tube that rocked out the best and gave the best, singing sustain. Even with this tube though, the Vibrato channel needed more brightness, which Mikey is only too happy to accommodate.
It was now after 10:00 so we decided to stop for the day. I packed up my guitars, left the DRRI for Mikey’s ministrations, and carried my stuff out to the car. Mikey and I stood outside for a bit talking about our day and what was to come next, the actual building of my amp. We could have kept talking for hours more but since I had a bit of a drive ahead of me, I wanted to get on the road while I was still charged up and alert. All the way home, I reflected on what a fine time I’d had at Mikey’s shop and of all of the new things I’d learned.
08 - Building the amp - Part 1
During the week after I left Mikey’s, he began to disassemble my DRRI. Every day or so, Mikey sent me digital photos of his progress. He also spent a lot of time emailing me the exact details of what he was doing and why. These have become a wonderful source of information for this article. Whenever I had a question about some aspect of the project, I’d send Mikey an email and he would patiently and thoroughly answer my questions. Here’s the first picture I’d like to share with you.
The PCBs, pots and jacks are removed during the disassembly of the DRRI
After removing the PCBs, iron, filter board, pots and jacks from the DRRI, Mikey built a brand new filter board and installed the Mercury iron. In the next photo, note that the black, phenolic octal sockets on the right that will be removed and replaced with high-quality ceramic sockets.
Mercury reverb transformer, new filter cap board, Mercury output transformer and choke
Since the Mercury iron is larger than the DRRI iron, the output transformer and choke are slightly offset. In order to keep the output transformer carefully away from the speaker, Mikey drilled a new hole in the chassis to properly position the larger output transformer.
The new filter cap board is a thing of beauty. In a quest for the best components, Mikey chose to use something other than the traditional Spraque Atom capacitors, although these are similar in appearance. They are smaller but have higher specs. For example, the Sprague 20uF caps are rated for 65 degrees centigrade whereas these can go to 85 degrees centigrade. Their tolerances are also tighter. Here’s a close-up:
Mercury reverb transformer and Mikey’s custom-made filter cap board
In this photo, you can see the high-quality workmanship on the polished board, turret installation, neat soldering and the use of the red, 18 gauge, stranded 600V Teflon wire. Mikey is primarily using Teflon wire throughout the amp. Mikey prefers Teflon wire because of the superior quality, the strands stay put when twisted and it is easier to solder because the insulation just won’t melt.
The next item on the agenda was the installation of the new, ceramic octal tube sockets. These hold the rectifier tube and the two 6V6 power tubes. Mikey chose ceramic sockets so there won’t be any chance of arcing and burning the sockets. He also reinforced the socket mounts by adding hex nuts to the socket mounting bolts, along with a dab of Locktite to make sure they stay firmly attached to the chassis. Here’s a nice photo of this section of the amp:
3 new ceramic
sockets (white)
DRRI power transformer (black), Mercury choke and Mercury output transformer
The power transformer is the stock one from the DRRI, which will be replaced next month with a Mercury Magnetics power transformer that is of excellent quality. Mikey offers this as an option.
09 - Bias Test Points
As previously mentioned, I elected to get the “bias test points” optional mod from Mikey. This does cost more but it is worth it to me. Having bias test points will let me replace the 6V6 power tubes myself using just a voltmeter or multimeter. Finding the right spot to place them in the amp without interfering with the back of the chassis is tricky. Mikey told me he was constrained by the slanted part of the back panel where it presses up against the back of the chassis as well as the rectifier socket on the inside of the amp.
Ground (black) and right and left (red) power tube test points
You can see an angled pencil mark indicating where the back panel lays across the rear of the chassis. On the inside of the chassis, there had to be room to fit the resistors between the red test points and the ground test point.
Internal wiring of the bias test points
In the photo above and the one below, you can see the bias test points are right near the rectifier tube socket. So as to avoid any problems, Mikey moved the B+ wire (red wire) from the pin on the rectifier socket so that it moves away from the bias resistors and runs along the bend of the chassis to the standby switch. It's out of the way of everything else. Mikey explained in an email to me another reason he likes to use 600V Teflon wire is that it gives an extra measure of insulation from other components.
The way the bias test points work is pin 8 of each power tube is wired to a red terminal on the inside of the bias test points. Each red terminal has a 1-ohm 1% resistor that goes to the black terminal, which is then wired to ground at one of the power transformer mounting bolts. Without bias test points, pin 8 is just wired to ground but adding this resistor allows a bias measurement in millivolts across the resistor, which converts directly to milliamps of current draw in the tube due to Ohm’s law.
Light blue wires attach at pin 8 of the power tube sockets to the bias test points
Although I’m jumping ahead of the construction process, the next picture shows the bias circuit portion of the main board created in “The Build – Part 3”. In the picture you can see the bias resistor, bias diode, bias capacitor and bias tap resistors, which create an “artificial” center tap from the power transformer.
The way this part of the circuit works is AC voltage from the power transformer enters the bias range resistor, which drops the voltage before entering the bias diode. The bias diode rectifies the AC voltage into DC negative voltage, much like the5AR4 tube does in the power section of the amp. This fluctuating DC voltage gets smoothed out by the bias capacitor on its way to the bias pot.
Bias circuit on the main board
The whole purpose of biasing is to set the right amount of current passing through the power tubes when no signal is present. Think of this as setting the idle on a car. If there’s not enough current, the tubes will sound sterile and won’t perform properly, and if there is too much current, the tubes will run too hot and there will be unwanted distortion and a good chance of tube failure.
The bias control on the bottom of the chassis is turned while looking at readings on the voltmeter, which has probes inserted into the bias test points. In this next photo, you can see the bias adjustment pot. Note that a screwdriver is placed in the white slot in the middle of the pot to turn it. As you can see, the bias pot can be turned from inside the chassis.
Bias adjustment pot as it looks from inside the chassis
What you can’t see is this adjustment can also be made from the bottom of the chassis without taking the chassis out of the cabinet. A screwdriver is simply inserted into a hole in the bottom of the chassis leading to this pot and the adjustment is made while watching a voltmeter attached to the bias test points, which are also on the outside of the chassis. Hooray. No lethal charges to fry guitar players! The voltage coming out of the bias pot goes to a junction with two resistors, which sends the right amount of separate negative voltage to the grids of each of the 6V6 power tubes. This negative voltage determines how much current goes through the tubes when they are at idle.
The bias is set to make sure the proper plate dissipation rating (in watts) of the
output tubes is reached. The maximum
plate dissipation rating for a single 6V6 tube is about 14 watts. Since it is best to operate at about 70% of
maximum plate dissipation, the bias is adjusted to bring the plate dissipation
down to about 10 watts (.7 * 14 = 9.8).
The calculation of the proper bias setting is done like this:
The formula to
calculate plate dissipation says that P = E * I, which means that Power (watts)
= Volts * Current Draw (amperes). Let’s
say the plate voltage is 400V. The
current draw (the unknown variable we need for setting the bias) can be
calculated like this:
P = E
* I
10 = 400 * I
10/400 = I