Super Reverb '65 RI - Changing Output Transformer to Match Speaker Load

[old guy]

As we all know, Super Reverbs are meant to drive their 4 ten inch 8 ohm speakers at a 2 ohm load. For the past year now, I've been running on 2 speakers only therefore, at a 4 ohm load. The amp is not as loud yet breaks up earlier and - overall; much sweeter

Coming from a lifetime of hating to mismatch anything, though no apparent harm has been done to the amp or speakers, I come to you to hear what you think about swapping out the stock transformer for a good quality one with a multi-tap wiring. This would allow me to pick a 2, 4, or 8 ohm load depending on what speaker cabinet or configuration I would run at whatever moment.

Questions:

#1. Is it just a matter of swapping out the transformer and NOTHING ELSE like, caps, resistors, widgets and wanketts and whatever ..... ?
#2. Will I be losing the pleasant audio gains I've achieved by the mismatch and essentially be putting it back to 'stock' - meaning losing my early
sweetspot?

Thanks.

[ThermionicScott]

If it were my amp, I'd make the switch in a heartbeat. Swapping the transformer should not be a big deal as long as it has the same mounting dimensions.

A SPTT (single pole, triple throw) toggle switch installed in place of the external speaker jack would make switching easy, too.

[Leo_Gnardo]

#1. Is it just a matter of swapping out the transformer and NOTHING ELSE like, caps, resistors, widgets and wanketts and whatever ..... ?
#2. Will I be losing the pleasant audio gains I've achieved by the mismatch and essentially be putting it back to 'stock' - meaning losing my early
sweetspot?

Thanks.

Like ThermionicScott says, yes change the OT. There will be changes in both directions: you'll be matching the impedance of the speakers you're using, otoh you'll be using only 2 speakers not 4, so a bit less oomph in the low end. Are you still using the 4x10 cab? What about the unused speakers? Still in the cab? Taken out but holes left? Taken out but holes covered? If unused speakers are left in the cab, or holes where they used to be, that will reduce the overall efficiency of your rig as well.

As far as circuit changes besides the transformer, I've done that change, made no others, everything works just fine. If you want to be a bit more exacting, a change of value of the feedback resistor would be in order. Ordinarily 820 ohms, you would increase that to say 1200 ohms FB resistor for 4 ohm tap. Not much of a change, I doubt anyone would hear the diff.

[g1]

#2. Will I be losing the pleasant audio gains I've achieved by the mismatch and essentially be putting it back to 'stock' - meaning losing my early
sweetspot?

Thanks.

Yes you will lose your sweetspot, unless you are planning to set the switch on the new transformer so it is mismatched.
The mismatch is reducing the power output of the amp, resulting in the earlier breakup.

[pdf64]

My finding is that the standard BF Fender load impedance of ~4k per 6L6 p-p pair is a bit low for max power output (max power seems to be ~5k), with an ~8k load giving pretty much the same power output as 4k.
The tone is slightly different though.

My guess is that the pleasant tone old guy has experienced may come from just being able to push the amp and speakers a bit harder.

[old guy]

My finding is that the standard BF Fender load impedance of ~4k per 6L6 p-p pair is a bit low for max power output (max power seems to be ~5k), with an ~8k load giving pretty much the same power output as 4k.
The tone is slightly different though.

My guess is that the pleasant tone old guy has experienced may come from just being able to push the amp and speakers a bit harder.

Thanks EVERYBODY!

Yes .. the pleasant, I don't need no stinken foot pedal to get my clean, overdriven tones, are a direct result of pushing the amp and speakers a bit harder .
The tones are incredibly usable in a club situation with both my ES-335 (Seth Lover pups) and Telecaster B-Bender (Bill Lawrence NF Singles).
Back the guitar Volume knob down to 8 for super clear but powerful rhythms, then, open 'er up to 10 for solos. Absolutely NO overdrive required!! I just worry about the mismatch causing some kind of failure. Then, you don't get paid etc etc etc...

I've been using a BB Preamp - something I consider to be one of the best - however; I'd rather have an absolutely clean stage floor! It reminds me of the 60s when all ya had was a Strat, a cable and a stack. No tap dancing on switches to take focus away from the show.

I think I'll buy me a new transformer with the multi-tap feature anyway. I'll install it with the switch in the extension cab as suggested. Besides Mercury Magnetics, can anyone say they've had great success with any other brand as far as 'upgrade' in tonal quality goes? I'm curious because the stock Fender tranny in the SR sounds incredible with my instrumentation and 2 paralled 8 ohm Fender Blue Alnico tens running at 4 ohms.

Of course, it all depends on what you're playing. I don't think a death metal guy would go for it.

[old guy]

Yes you will lose your sweetspot, unless you are planning to set the switch on the new transformer so it is mismatched.
The mismatch is reducing the power output of the amp, resulting in the earlier breakup.

That's what I was hoping NOT to hear. Oh well, at the very least, I'll still be able to use different speaker cabs I have.

[ThermionicScott]

That's what I was hoping NOT to hear. Oh well, at the very least, I'll still be able to use different speaker cabs I have.

I think you might have stopped reading g1's post too soon... you'll still be able to select the mismatch you're enjoying now.

What's happening with this mismatch is that the tubes clip much sooner, but the tubes also go into cutoff later, so it ought to sound pretty good. The main concern is that this is harder on the output tube screens, but it sounds like they are tolerating it okay. You might consider replacing the 470Ω screen resistors with 1kΩ/5W units just to be on the safe side.

[pdf64]

I'm very happy to use Hammond transformers, eg https://www.hammfg.com/files/parts/pdf/1750M.pdf
They seem to give great performance and I've no reason to suspect other brands would be an improvement, though I've never tried eg MM or Classictone.

[Leo_Gnardo]

I think I'll buy me a new transformer with the multi-tap feature anyway. I'll install it with the switch in the extension cab as suggested.

Why install transformer OR switch in the ext cab? Best in the amp, both.

Besides Mercury Magnetics, can anyone say they've had great success with any other brand as far as 'upgrade' in tonal quality goes?

Tubesandmore/Antique has the transformer you need, it's intended for Bassman/SupRev and any other amp that would like to go 2/4/8. Good price too.

Mercury may promise a "tonal upgrade" but all I've heard from amps that had their iron installed as replacement OT, is extra bandwidth in the high end, IOW ice-pick highs. If you want to break glass with your tone, be my guest and empty your wallet at Mercury. My customers & I are not impressed. But who knows, somebody's gotta like 'em, they sell enough. I reckon those Alnico blue 10's are plenty bright enough already.

[ThermionicScott]

Why install transformer OR switch in the ext cab? Best in the amp, both.

I didn't catch this the first time around, but my suggestion was to replace the external speaker jack in the amp with the selector switch, not at the cab. Can't speak for anyone else, but I never use external speaker jacks anyway!

[TimmyP1955]

Fender Output Transformer, Hot Rod DeVille, Blues DeVille, Bassman, Super Reverb, Concert, 2/4/8 Ohm, M-6 Upgrade 

[Leo_Gnardo]

Fender Output Transformer, Hot Rod DeVille, Blues DeVille, Bassman, Super Reverb, Concert, 2/4/8 Ohm, M-6 Upgrade*

Good find at $68.80!

Also Antique's Hammond P-T1750M, Antique# 003486 $75.74.

And Hoffman's Heyboer (I'm pretty sure) 018343 $80.00

Choices, choices, choices...

[Chuck H]

No one mentioned yet (ok, pdf sorta did)...

Fender amps are historically tolerant of a 100%mismatch in either direction. I'd bet six beer (craft PNW) the amp has been happy as a clam this whole time and would continue to be if left unmolested. If I had ever nailed my tone nirvana I wouldn't be making amps. Many of us wouldn't and there'd be no one for old guy to bounce this off of. I wouldn't mess with it. Why jeopardize your perfect elemental tone? And at some expense anyway. Maybe build a SR clone head with a multi tap OT for use with other cabs. That way you never lose what you already have. We've seen it here before. First there's the wanting and working. Then the chasing and troubleshooting, then the whining and crying. Too soon "The amp still doesn't sound like it use to" and whole thing is crapping the sheets. There are a lot of amp possibilities. Almost an infinite number of options. Why put "THE" amp on the chopping block? JM2C on that.

[The Dude]

I was going to chime in with a similar statement earlier, but passed at the risk of being chided. I will, however, agree 100% with Chuck's post. There are plenty of Fenders out there in the world that have been run for years at the wrong speaker impedance, I'd suspect some since they were built. Although not recommended on paper, I wouldn't think twice about a slight mismatch. Imagine how many players are out there that have no idea what that number even means.