Silverface Twin Reverb vs. Blackfaced Dual Showman Reverb

Jim Cooley · From: The 'Ville, Texas, USA

I am interested in a blackfaced 1968 Dual Showman Reverb listed on the forum:

https://bb.steelguitarforum.com/viewtopic.php?p=2806321#2806321

I have a 1972 silverface Twin Reverb, master volume, modded to reverb on both channels. The Twin is in a head cabinet, so I have several choices of speaker configurations and the weight reduction is nice. I know there are several similarities between the two amps, but the Showman's being blackfaced is what has me interested, because well, it's "blackfaced" and so many steelers and six string guitar players swear by them. I am aware that there are different "blackface specs" and that Fender continued to make blackface amps after CBS bought the company. I've also read that early silverface amps were essentially the same as later blackface amps. Consider all that and recognizing that tone is subjective, what differences, if any, might be expected?

Dave Meis · From: Olympic Peninsula, Washington, USA

Is there a 'standardized' process for 'Blackface-ing' an amp? Not sure how the Silverface Showman would differ from the Silverface Twin, but would like to know more about the Blackface-ing process!

Barry Coker · From: Bagley Alabama, USA

From what I've read The Twin Reverb and the Dual Showman are the same amp as far as electronics same tubes and same power about 85 watts (as per Fender). The diffrence is in
the one or two pice cabnet.
As for Blackface/Silverface The blackface has diffrent tone capasiters and some like the Pro Reverb and Delux Reverb had a Tube rectifier. One of the electronic Guroos on here would know way more details than me but I think there is a standard silver to blackface conversion.

Ken Fox · From: Nashville GA USA

From an old website I used to visit called Machine Gun Amps:

Modding a silverface amp to blackface specs.

Silverface amps all sound better when modded back to blackface specs in my opinion. I will outline the mods below. However, some of the changes that Fender did in the silverface years are not easily changed back to blackface specs.

Don't go into the amp unless you know how to not get shocked! These amps will even shock you when unplugged. They store extremely harmful voltages that will jump out and grab you if you put your paws in the wrong place. I know this from experience! It hurts!

Suppresser caps: Fender added .002uf (or sometimes 1200pf) capacitors to the grids of the power tubes (pin 5). These bleed off frequencies that they thought were too high to be heard with guitar. The effect of these is to bleed off any frequencies that the amp will oscillate at. Oscillation is like feedback with a microphone. It feeds itself and runs away from you if you don't do something about it. Amps can do this internally, and it's a big problem. For you tech types, somebody emailed me and said that the effect of these caps is -18 dB at 6 kHz! Ouch! The caps are actually a good idea, but they tend to bleed of high end "sparkle" from the amp. These caps were added because of problems with the lead dress that was causing the amps to oscillate. It's unfortunate that Fender needed these. The best way to control oscillation is to design the amp not to oscillate in the first place! But for cost cutting's sake, it was cheaper to put these caps in than spend the extra labor to make the amp more stable. These caps can usually be removed and the amp will run fine. I haven't run across an amp yet that started oscillating without them. But, I have heard from some techs that have seen many amps that can't live without these caps. Oscillation suppression is nothing new in Fenders. Tweed bassmans had a cap across the plates of the phase inverter to help with this (47pf). If your amp plays fine after the mod and then all of a sudden acts like it looses most of it's power, it is probably oscillating. Try the 47pf cap like the tweed Bassman and see if that fixes it (look in schematics to see how it is done). There is also a much rarer oscillation suppression method Fender had, it involved a .02 cap and a 220k resistor going from one leg of the power section then held 100 ohms above ground via the feedback loop. This is rare and only occurred in the early 70's.

Phase inverter: Fender changed the phase inverter in a few ways. Starting from one end and going to the other: The coupling cap increased from .001 to .01. This has the effect of letting more bass through to the power section. This sounds like a good idea, but to my ear makes the bass get overbearing. The .001 cap sounds tighter with more defined bass to me. After that, Fender used 330k resistors on the grids of the phase inverter instead of 1 meg. The cathode resistor on the phase inverter was made smaller which ran this tube a little hotter. The plate load resistors were decreased from 82 and 100k to 47k. This reduces gain. Overall, the changes to the phase inverter look like they were designed to tame the amp and change the way the amp sounds to what Fender wanted at the time.

Reverb circuit: Fender tended to run the reverb driver tube very hot in the silverface years. Blackface amps came with 2.2k resistors bypassed with a 25uf-25v electrolytic cap. Sometime in the 70's, they started to change this value. I've seen 1.5k, 820 and 680 ohm resistors here without a bypass cap. Fender also added a cap from the plates of the reverb driver to the cathode. They added a cap to ground after the reverb tank as well. I've found that I sometimes like the silverface method for reverb better than blackface, but I do take out the added caps to ground. I will leave the amp otherwise stock if the reverb sounds good to the owner.

Bias supply: Fender changed the bias supply from a level to a balance control. The balance control allows the tech to match the tubes, but not set the bias level which is what can determine tone. Also, some extra filtering was added to the circuit (two 70uf-100v's? Don't remember exactly). I always change the bias supply to blackface specs because we use matched tubes these days! When replacing the bias supply filter caps, I usually just use one 100uf-100v.

There are a few other changes that I don't mod back to blackface specs because I don't feel they change tone all that much. The main ones have to do with the power supply.

Changes in the silverface years that can't easily be changed back to blackface specs: Sometime when Fender went to the 5U4 rectifier tube, they increased voltages on the high voltage secondary of the power transformer. The 5U4 has a higher loss, so the increase makes the voltage after the rectifier tube similar to what it was in the blackface years with a GZ34. When installing the GZ34 in these silverface amps, the voltages will be higher than those in a blackface amp sometimes. The only way this can be changed back to blackface is to change the power transformer. This is expensive. In the late silverface years, Fender changed the power supply and power section of the amp quite extensively. They do not look like the earlier blackface and silverface amps at all. These changes included new power and output transformers and solid state rectifiers for all of the larger amps. Voltage was greatly increased on the plates of the power tubes. These changes are not easily reversed. The way to tell if you have one of these amps is to look under the speaker jacks. If it says. 70 or 135 watts, you have the later model that cannot be easily or cheaply modded back to blackface specs. I'd recommend selling this amp if you are not happy with the tone before trying to do extensive and expensive mods to it. They actually do sound pretty good clean though. And they are extremely loud!

Dave Meis · From: Olympic Peninsula, Washington, USA

Thanks Ken! Now I know! Smile

Godfrey Arthur · From: 3rd Rock

Tom Wolverton · From: Carpinteria, CA

One other thing Iâ€™d like to add is this. With a Fender Twin Reverb, the reverb pan is at the bottom of the cabinet. It is fairly far away from the rest of the ampâ€™s chasis. With the Showman Reverb, the pan is much closer to the chasis. This often causes increased hum in the reverb circuit.
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Bobby Nelson · From: North Carolina, USA

A BF Twin Reverb is 85W and an early silver is 100W - kind of a dumb question but, does that translate to a significant loss of headroom? My 73 sounds great and I won't be tinkering with it but have considered getting a BF.

Charley Paul · From: California, USA

You wonâ€™t run out of headroom with any Twin. The silver face might stay s bit cleaner at volume than the blackface, but neither will crunch like a Deluxe. They are clean machines. The blackface version has a nice warm sound, and the silver face snarls and spits a bit more. I think, when properly serviced, either amp is a great choice for steel.

If memory serves me right, the Dual Showman shares the same electronics as the Twin Reverb.....but comes in a head and does not have Reverb. The â€œTwinâ€ part of Twin Reverb has to do with the dual 12 inch speakers. Those speakers are a big part of the sound.

I recently bought a 1966 Pro Reverb and it is just about perfect for steel. Perfect headroom that allows me to turn the amp up enough to to find the sweet spot, and has the perfect amount of warmth. I donâ€™t play places that allow me to turn a Twin up loud enough to sound right....even outdoors the Pro Reverb is perfect for me. And itâ€™s smaller and lighter than the Twin. But it still has those two 12 inch speakers which give it a huge, full sound. Mine has 2 Jensen Concert speakers in it.....they basically fall in between classic Jensen ceramics and JBLâ€™s. More full range, but not clinical sounding. Perfect for me. And Pro Reverbs are kind of underpriced these days....I bought mine for $1500 all original, and already serviced (caps, grounding, etc).

Paul Sutherland · From: Placerville, California

I have both a 1971 Silver face Twin Reverb and a 1970 Dual Showman (non-reverb). My service tech told me that the Twin has an extra gain stage due to the reverb circuit, so it sounds somewhat different. I agree with his assessment. The Twin is noticeably louder and has more low end response and clarity. I like both amps but I tend to use the Twin more than the Dual Showman.
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Mike Schwartzman · From: Maryland, USA

The post by Ken Fox copied from the old Machinegun Amps site was a guide used by many. It was pretty informative on the topic. A lot of 6 string players were looking to "warm up" the Silver Face Twin Reverb by bringing it back to Black Face specs.

But Jim...even though the amp (Dual Showman Reverb) that you are looking at is basically a Twin Reverb in a head version, remember it is a 1968. And the changes in 1968 were in a lot of CBS Fender amps largely were cosmetic that year when the faceplate changed from black to silver and the cabs had the silver "drip edge" added. I opened up a 1968 Bandmaster back about 15 years ago and when I saw the original components and the original lead dress (wiring layout)... it was a blackface circuit from the factory to begin with.

So the first Dual Showman Reverb's 1st year was 1968. So it's possible that the amp may have been partly built and wired like a mid-60's black face twin anyhow, but only looking inside would tell. Fender used 2 or 3 different circuits in that model over the years. In any case, pick a proper speaker(s) and that amp would be great for PSG in BF or SF IMO. Nice looking head cab on that DSR too.
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Stephen Cowell · From: Round Rock, Texas, USA

1968 was a special year for Fender amps... most of them got the 'bias cap' treatment, where they put some cathode bias into the final amp. They also messed with the phase inverter. 'Blackfacing' a Twin removes these mods and takes it from AC568 back to AB763 specs.

https://schematicheaven.net/m-fender.html

Another special thing about '68s is the cloth wiring... cloth wiring is desirable because it stays where you put it. Fenders are sensitive to lead dress... Aspen Pittman (Groove Tubes) says to lift the grid wires up and press the plate and cathode wires against the chassis... obviously you can't do this with plastic wiring, it just goes where it will.

You can tell a '68 by the drip-edge stuff around the speaker baffle... one year only. They used to be cheap, but folks have found out about them.
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Bobby Nelson · From: North Carolina, USA

That's good info Charlie, thanks. I may look into a Pro. I had a SF pro with Pyle drivers in it, but it didn't sound too good with my Stratocaster.

Richard Sinkler · From: aka: Rusty Strings -- Missoula, Montana

ajm · From: Los Angeles

Converting a SF to BF: In one of Gerald Weber's books he had a write up on how to do this.
As I recall it sounded fairly easy and was 3-4 steps.
I don't know how closely it compares to the one posted above.

Tom Gorr · From: Three Hills, Alberta

Stephen Cowell: yes.. I recall talking to my tech asking him to put the cathode bias in my SF amp. Nothing sweeter than a little bit of cathode bias in an amp.

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