Rebuilding a Deluxe Reverb Reissue Tube Amplifier with Mikey

As I mentioned earlier in the article, I had not originally intended to use a Mercury Magnetics Power Transformer (PT), electing instead to save a little money and use the stock DRRI PT. I’ve since changed my mind. How this came to be makes for an interesting story.

About 10 days before I was scheduled to pick up my amp at Mikey’s shop, I sent out emails to all the companies that I linked in this article. This included Mercury Magnetics since Mikey was putting their output transformer, reverb transformer and choke in my amp. Shortly after sending out an email to Mercury, I heard back from Paul Patronete who graciously gave the OK to link to their site. He also took a moment to let me know in addition to the other Mercury iron I was using, their power transformer would make an improvement in the tone of my amp. Paul invited Mikey and me to give Sergio Hamernik (an owner of Mercury Magnetics) a call to discuss the benefits of the power transformer.

I really appreciated the helpful suggestion but I hadn’t ever heard of a PT making a difference in tone, thinking the other pieces of Mercury iron would make 90% of the improvement. I did let Paul know I’d add a comment in this article saying I’d heard from Mercury and the PT would make a big improvement in the tone. He wrote me back with an interesting bit of information I had never considered. Here’s a paraphrase from the email he sent me:

The stock reissue PT does an OK job of supplying the required voltages to the circuit however the overall PT's behavior under working conditions is not the same as the original vintage Deluxe Reverb PT. Characteristics that make the reissue PT different than the original PT involve flux density, AC regulation and primary inductance. These characteristics are a very important factor for the player that wants to nail the tonality of the vintage Blackface Deluxe Reverb amp.

Paul once again encouraged me to talk to Sergio. This certainly piqued my interest so I got in touch with Mikey and discussed Paul’s comments. We decided to get Paul on a conference call and to also see if we could speak to Sergio. We called Mercury in the late afternoon, four days before I was due to pick up my amp. Although Sergio wasn’t in, Paul spent almost 1.5 hours talking with Mikey and me about their power transformer and the rest of their iron.

Paul is a guitar player first and foremost and his enthusiasm for great tone is infectious. In addition to talking about all the good things Mercury Magnetics has brought to the industry and guitar players, he talked about what some of the cutting edge builders are doing. Mikey and Paul had very similar opinions on what makes great tone and why. It was a very informative and fun conversation. At the end of it, I certainly wanted to speak to Sergio so Paul invited Mikey and I to call again in the morning.

The next day, Mikey and I called Paul and after a brief chat, he brought Sergio to the phone. It was truly a treat to talk with Sergio and I learned a LOT about tube amps, the importance of an amp’s magnetics (the iron) and primarily, the benefits of using a Mercury Magnetics power transformer engineered for a Deluxe Reverb. As we talked, I jotted down as many notes as I could manage. I’ll share them with you now, although please keep in mind I may not have captured everything Sergio was conveying. He did a fine job though of keeping his information geared to my level of understanding.

Sergio started by asking me if I knew what modulation is. Of course I’ve heard the word but I wasn’t sure what it meant in relation to tube amps. He explained an amplifier is a modulated power supply whereby the guitar signal is used to modulate the amp and so the quality of the power transformer affects tonality. He said the power transformer (along with the rectifier tube, a 5AR4 type) is responsible for taking the AC wall current and transforming it into the DC current used in certain parts of the amplifier. He said the power supply sets everything else up and everything depends on the character of the power supply. For example, since it helps determine the AC and DC voltages going to each section of the amp and tubes, it has a big impact on the feel of the amp.

I learned that although the stock DRRI power transformer provides the right amount of volts and amps (current) to the amplifier, the DRRI power transformer is nothing like one of the original PT’s used in Deluxe Reverbs. Sergio said among other things, the flux density and primary inductance all have to be right. As a comparison, the DRRI stock power transformer has 1/2 or less inductance on the primary than a Mercury Axiom PT. (You may recall from a previous section; inductance is the opposition to changes in current.)

He said capacitance and leakage reactance are critically important and Mercury Magnetics power transformers have lower flux density and heavier iron with better permeability. Capacitance and leakage reactance between the windings, and where the filaments are in relation to the B+ supply, really matters. Now that’s a mouthful! I think I’ll need to spend some time researching the concepts mentioned in just the last two paragraphs so I can better understand the electrical theory behind his designs. One of the best things about this project and writing this article is being exposed to new concepts. This is my idea of fun!

Sergio did break this theory down into practical examples for me. He explained the Mercury Magnetics method starts with finding the very best sounding amps and examining their iron. For example, if there is a great tone on a recording, Sergio can try to find the exact amp used on the recording and use it as the model for new iron.

The DRRI power transformer has different physical dimenstons than the one in a Blackface Deluxe Reverb. Mikey has an electronic caliper that does very precise measurements so he sent these dimensions to Paul so Mercury can provide the perfect power transformer for this amp. They have the know-how to build a power transformer that will sound just like one in a Blackface Deluxe Reverb. They do this by using the very best example of an original 1965 Deluxe Reverb transformer, unwinding it and laboriously documenting every nuance of how it is constructed. Then a combination of old and new technologies is used to create the very best transformer possible.

There’s a reason why guitar players seek out older amps, and this obviously is because of better tone, which I’ve come to understand is largely due to quality magnetics. I learned the magnetics available to amp builders in the 50’s and 60’s were made from materials optimized for the military for WWII and the Korean War. There was a tremendous overstock from the military build-up and amp builders had ready access to very high quality materials.

Modern materials are designed to be cheaper to hit price points. Sergio told us he specs custom steel to make Mercury transformers. They do enough volume of business that he can insist his steel manufacturer hand crank the steel through a gas oven, just like it was done in the 50’s and 60’s. Steel and copper behave differently at different milliamps so the properties of the metal must be designed and manufactured to this end. For the guitar player, this level of quality shows up in things like the ramp rate of note attack, the feel of the pick attack and better bass note response. He also used the choke as an example, where the Q-Factor (the measure of quality in a resonance system) is quite a bit different between the stock DRRI choke and the Mercury choke, so much so that it makes for an audible difference.

Sergio explained the power transformer is rated for a lot more watts than the amp produces. For example, the Mercury Magnetics Axiom power transformer for my amp will be rated at 120 watts and is capable of supporting an audio output of up to 60 watts. The general rule-of-thumb is the power transformer needs to be rated at twice as much as the maximum audio output.

Since this power transformer has specs well in excess of what the two 6V6 tubes are capable of creating, it can safely run 6L6 tubes. 6V6 tubes require only 60% of the power of 6L6 tubes. The output transformer is also capable of handling 6L6 tubes so by getting the Mercury Magnetics power transformer, I can get more power and a different tonality out of my amp than with the 6V6’s. This is a nice bonus and one I hadn’t considered when Paul first emailed me, suggesting their PT. I prefer 6V6’s in the amp but it’s nice to have another option.

Mikey asked Sergio to describe the sonic differences we might expect with the use of the Mercury Axiom reverb transformer. Sergio said the sound differences are subtle because it is such low power but if you have good ears, you’ll hear differences in “evident detail” and a “perceived wider bandwidth".

Mikey and Sergio talked a bit about the dramatic effects of using the Mercury output transformer. Sergio likened his output transformers to a window with no glass and no screen, allowing all of the tonality of previous sections of the amp to pass through with great clarity. He explained the excellent “phase relationship tonality” (perceived as a 3 dimensional swirl) is dependent on the quality of the construction of the transformer. By comparison, the DRRI output transformer acts as dirty glass covered by a dirty screen. I couldn’t help but be reminded of the scene from the movie “My Cousin Vinny” where Vincent Gambini (Joe Pesci) disproved the testimony of a witness by pointing out with pictures how the witness was looking through dirty glass, a bug covered screen, and through trees and bushes at a fleeing car.

As a tube amp enthusiast, I’ve been reading and learning about tube amp electronics for quite some time. In this conversation with Sergio I learned a lot of things I had never considered. Of course, by now I was completely convinced their power transformer should go in my amp! You can understand why the top amp builders call upon Sergio for his expertise, designs and remarkable archive of information.

If you take a look at the Mercury Magnetics site you will find a large selection of iron to fit just about every need.

Sergio and Paul both told us there were very significant differences in iron on the same models of amps from the same era. Sergio spoke of a conversation he’d had with Leo Fender about amp components. Leo told him the Fender Company experienced a swelling of demand for amps when young people became enamored of guitar. Fender was just trying to meet the enormous demand so they put out specs for things like power transformers to various suppliers. The suppliers had a lot of latitude in how they meet the specs, creating a lot of variation in the parts.

Here’s another new bit of tube amp knowledge I learned from Sergio. He explained that all magnetics (iron) in an amp need to be broken in over a 20 to 40 hour period of playing time. He said initially, there’s a slight harshness in the tone, which can also be characterized as a lack of sweetness. The magnetics have to be thermally and magnetically cycled. Apparently, it is similar to breaking in a speaker. Paul later told us he’s had guitar players call him up after a month to describe the new subtleties and complexities emerging from the amp: a wonderful and unexpected surprise.

After spending about 45 minutes on the phone with Mikey and me, Sergio turned us back over to Paul. I must say it was a pleasure and an honor to speak with Sergio and he couldn’t have been more gracious in taking his time to explain all of the information I’ve relayed above.

Paul and Mikey made arrangements to take the exact measurements of the bolt placement and chassis openings in the DRRI for a new power transformer. I sat back for a bit as Paul and Mikey continued where they’d left off the night before, talking about new amp ideas Mikey has been considering, which will involve creating an amp using a wide variety of power tube options. It’s too early to go into details about that though. I’ll have to save that for another article :>)

By the way, we got to know a bit more about Paul Patronete. He is a key associate of Sergio who talks with guitar players and amp builders all the time, helping people decide which Mercury Magnetics iron is right for them. You can tell he really gets off on helping players attain tonal nirvana.

Of interest, before coming to Mercury Magnetics, Paul was the General Manager for Groove Tubes for many years. I dug out my copy of Aspen Pittman’s “The Tube Amp Book – 4th Edition” and sure enough, there is a picture of Paul on the inside of the back cover. He’s also listed in the very front of the book in the “Strokes For My Folks” page and a color photograph of his Orange amps is also in the book.

Well, I’ve gone through all of my notes from my discussions with Paul, Sergio and Mikey so I guess it is time to close this chapter. I’ll be picking up my amp tomorrow, although it will have the stock DRRI power transformer in it until a new one is manufactured. I sure am glad Paul took the time to talk to me, educate me, and with Sergio’s help, convince me to get a Mercury Magnetics power transformer to go along with the rest of the Mercury iron in my amp. I’ll make another trip to Mikey’s shop in Baltimore next month and I’ll be sure to let you know how it sounds, so stay tuned.

In October, I returned to Mikey's shop for the installation of the new Mercury Magnetics power transformer as well as some additional tweaks. The PT is covered here and the rest of the visit is covered on the "Another Visit to Mikey" page.

The new PT is a beauty and it is just HUGE. Here's a picture of it next to the original DRRI PT.

As you saw at the top of this page, Mercury didn't initially offer an Axiom PT as a high-end drop-in replacement for a DRRI rebuild. This all changed when Paul and Sergio learned of this project and created one specifically for this task. Here's a photo of the top. Note the creation date is 9/04 (September, 2004). It is a model FDR-PRI, which stands for Fender Deluxe Reverb Power Reissue.

It is really cool to have had a small role to play in the creation of this new power transformer. Many thanks to Paul and Sergio for making this happen!

I was curious to learn exactly how this power transformer would be installed so I took careful notes during the installation. Some of the wires are solid in color and others have a second color as a band.

1. The Green/Yellow wire would be used for a center tap if Mikey had not already created an artificial bias center tap as described in the "Bias Test Points" section. As you'll recall, the original DRRI PT didn't have a center tap wire for this purpose, which isn't uncommon. In this case, Mikey put a piece of heat-shrink over the clipped end of the wire, coiled and taped it and tucked it under the main board.

2. The Red/Yellow wire is the center tap for the AC secondaries. The PT transforms the 120 volt input from the wall outlet into 370 volts on this wire. It is connected to the PT mounting bolt and serves as the relative ground for the power supply components. Connected to this bolt is a black wire for the ground supply for the power circuit on the main board. Another black wire connects to this bolt for the first filter cap.

3. The Red/White goes to the bias supply and is approximately 45 volts (it isn't shown on the diagram for the PT from Mercury). This attaches to the bias resistor in order to drop the initial voltage. This is the blue resistor at the far left of the board.

4. The two twisted Red wires carry the 347 volt AC secondary from the PT to the rectifier tube at pins 4 and 6. The rectifier converts this AC current into DC, which is on pins 2 and 8 of the rectifier tube.

5. The two twisted Yellow wires carry the 5 volts AC required to heat the filament of the rectifier tube.

6. The two twisted Black wires of the primary carry the 120 volts AC from the wall at the power switch into the power transformer, arming the PT with power.

7. The two twisted Green wires supply the 6.3 volts AC needed to power the pilot light and then the filament heaters of the preamp tubes. As you can see, they are attached first to the pilot light assembly.

Once the new power transformer was installed, Mikey had to change the bias range resistor from 470K to a 3W/2.2K in order to get the bias in proper range. We hooked up the volt meter and set the bias so the meter read 26mv.

I really learned a lot from Paul and Sergio about the importance of high-quality iron in an amp. This PT has made a noticeable difference in the sound of the amp. You can see my comments in the "Playing The Amp" section.