Super Reverb

[pbiagi]

Bought a '64 Super Reverb off ebay a few years ago and opened for first time recently.

I've built a few amps but since this is vintage don't want to make a change which impacts its integrity.

The transformers and chassis serial nos. check out to ~'64, however it appears the power transformer was changed out.
Please let me know any insights you see from the photos.

A few questions:
- it appears the heater wiring is both center tapped and referenced to ground with 100 ohm resistors (I assume), see photo. Not a good idea? Should I lift the heater center tap?
- the bias circuit cap is 50uF but the AB 763 circuit says it should be 25uF. Does it matter?
- the electrolytics are changed out (good), but no other caps. Would like to replace the ceramics with silver mica, but would that impact the amp vintage integrity?
What about the others? I have a DMM which could measure them but believe they'd need to be removed from circuit.
- the (believe it's called) 'death cap' is present. Should I disconnect that?

Any other advice?

[Enzo]

Lift the center tap or get rid of the resistors. No, you don't want both. I'd ditch the resistors myself.

Bias filter cap. Note the schematic says 25uf 50v, then look above where it says 52v of bias, meaning the actual bias supply is even higher. 50v is not high enough. You need a 63v or better yet a 100v cap. I generally install 100uf/100v myself. if it isn;t original it isn;t original, the value won't change that. And there is no sag to speak of on that supply.

For better or worse, vintage means vintage, not rebuild or reissue. I'd rather have a working amp, but a collector might prefer all original even if it doesn't work well. Pulling the ceramics for something else will make it that much less original. Up to you whether you value performance or vintageness.

There are ceramic caps in the signal path, but not all of them are, for instance the three in a row are your tremolo oscillator feedbackj caps. The signal does not run through them, so why change them?


The death cap is the one connecting the4 ground switch to chassis. If you have a three-wire power cord, then get rid of it. If you still have a two-wire power cord, get rid of that and install a three- wire one.

[soundguruman]

Bought a '64 Super Reverb off ebay a few years ago and opened for first time recently.

I've built a few amps but since this is vintage don't want to make a change which impacts its integrity.

The transformers and chassis serial nos. check out to ~'64, however it appears the power transformer was changed out.
Please let me know any insights you see from the photos.

A few questions:
- it appears the heater wiring is both center tapped and referenced to ground with 100 ohm resistors (I assume), see photo. Not a good idea? Should I lift the heater center tap?

No you don't need to do that

- the bias circuit cap is 50uF but the AB 763 circuit says it should be 25uF. Does it matter?

50 produces more bass, 25 less bass, 70 is the max bass
100 is too much bass. It will sound muddy in the low end.

- the electrolytics are changed out (good), but no other caps. Would like to replace the ceramics with silver mica, but would that impact the amp vintage integrity?

silver mica is less hum especially on the bright switch. There is no vintage integrity on an amp that has been overhauled like this one.

What about the others? I have a DMM which could measure them but believe they'd need to be removed from circuit.
- the (believe it's called) 'death cap' is present. Should I disconnect that?

Yes get rid of the death cap. You can install the UL approved one if you want.
The three wire (grounding) power cord should be installed, if not done already.

Any other advice?

Yes, don't electrocute yourself.

[ATTACH=CONFIG]22298[/ATTACH] [ATTACH=CONFIG]22299[/ATTACH] [ATTACH=CONFIG]22300[/ATTACH]

Have fun with it.
(Fender Authorized Technician, for Life)

[Enzo]

50 produces more bass, 25 less bass, 70 is the max bass
100 is too much bass. It will sound muddy in the low end.

Please explain in detail how these values of filter cap on the BIAS SUPPLY would have such an effect. We are not talking about the B+ here, just the bias supply. Bias supply is not subject to current draw.

Edit to ad:

Just to help you, here is some data -
AB763 25uf 50v
AA270 50uf 70v (each of two filter stages)
Rev J 80uf 75v (each x 2)
1976 80uf 75v (each x 2)
1978 70uf 100v (first stage) 80uf 75v (second stage)
1981 70uf 100v (each x 2)
2000 100uf 100v (reissue amp)

[soundguruman]

The value of the cap sets up a low frequency resonance in the output circuit.
Most techs do not realize this.
See, you learn something new every day.

[Enzo]

Utter bullshit, please explain HOW it happens.

[soundguruman]

Utter bullshit, please explain HOW it happens.

I would like to know first
What imaginary privilege do you have to attack, berate and swear at other members of this forum?
which I may add, you do pretty often...

I am under no obligation to acquiesce, concerning your bullying.

Concerning the fact that others, with musically trained ears, hear or detect musical qualities that you don't hear.
(or for that matter, can't hear)
I think essentially what I may be inferring is that you are not a musician, and that you are tone-deaf (maybe).
And that you wish to assert your superiority to others by wholly rejecting the observations of others more musically qualified than yourself.

My first recommendation is that you sign up for guitar lessons, or ear training.

[Steve Conner]

He has the privilege of a post count over 17,000, almost all of which have been packed with helpful information. I don't think I buy the low-frequency resonance thing either. Did you ever scope the bias voltage and see it oscillating?! I can't see how that could be possible.

[pdf64]

Yes, surely 'a low frequency resonance in the output circuit' is a measurable effect, no golden ears necessary.
Pete

[J M Fahey]

The value of the cap sets up a low frequency resonance in the output circuit.
Most techs do not realize this.
See, you learn something new every day.

Utter bulshit [2]
Now, why doesn't this surprise me?

Is there anything to learn from SGM's "Tech" posts?

Yes , of course: the Lesson is:
SGM has no clue, but he will post anyway.

[pbiagi]

Thanks Enzo for calling out BS when it's written - truly appreciated by especially those trying to learn!
I'm no expert .. but we're talking about a bias circuit - even I saw that.
SGM, I don't care to hear more from you on this thread and have reported you.

BTW, the transformers may not be original, but they do appear to date to '64/65.

Back to the amp -
Overall I prefer a well performing amp and will go there. Just don't want to do something stupid.
The amp does have a 3 prong chord.
Will go for the 100uf/100v bias cap. and replace ceramics in signal path.
Tonight I'm going to check out the filter caps, and will be ordering soon.
Question: For where I want to go I should replace the coupling caps too? (I think these are existing but assume they could have dried out.?)

Some day I'll probably replace speakers with Weber's. Can always change out.

[JoeM]

Unless a specific cap (not the electrolytics) is defective, I wouldn't change them, even the ceramics.

[pbiagi]

Here's a picture of the filter caps.
Sprague Atoms for first two, good, but the Mallory's I assume are very old, need replaced? Would 20uF/600v fit?


JoeM, From what little I know, I'd need to remove each cap. to measure to check if they were defective.

[pdf64]

I think that the Mallories are from 1984; my experience of these is that they are very long lived caps. I've only seen a failed one once. I've left them in my 1982 Fender 75, and do so with most amps I refurbish, unless the owner needs the re-assurance of new caps.
All the coupling caps are very probably fine; if one was bad you'd probably know about it, there would be a symptom.
The failure modes are usually dc leakage, and very high ESR, ie effective open circuit.

I'm concerned that we've been overly harsh with soundguruman; he has some quirky views but who's to say they are all wrong?
With regard to decoupling cap values, I've noticed that very well decoupled B+ preamp supplies can seem bassier than those that are less well decoupled, but it would be difficult to put a number on it. So there may potentially be something to his view about bias supply cap values, even is it's just an 'edge of perception' / golden ears thing.
I concede it can be frustrating when such opinion is expressed as if it's gospel.
Pete

[JoeM]

JoeM, From what little I know, I'd need to remove each cap. to measure to check if they were defective.

No, not at all. Replace the electrolytics first, and then play the amp. I bet it will sound great. If there's a symptom of trouble somewhere you should hear it.