Super Reverb

[Steve A.]

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...

We do have freedom of speech here in the US. Enzo can say what he wants and you can say what you want about it. Enzo says it like it is but I have never seen him be abusive. I'd have to say that he is probably the most experienced and most helpful of all of the full-time amp techs that frequent this forum. (No offense intended towards the other full-time amp tech on this forum, whoever you might be. )

So how exactly does the filter cap in the bias supply circuit affect the low frequency response? It does make a difference in the cathode resistor bypass cap in the earlier Fender amps but the amp in question is a BF Super Reverb. BTW it does help the frequency response a lot if the bias supply filter cap is installed with the positive terminal to ground.

Steve Ahola

[Enzo]

Let us be honest, Guruman, the only one on this forum I berate is you. And I do it because you are the one person on this board who consistently just makes things up and posts them. Novice techs - the people I try hard to help - come on this board and they don;t know the difference when you spout some nonsense. I feel the need to look out for them in the face of your onslaught of baloney.

You blathered that various filter cap values in the bias supply would make the amps too bassy, yet there it is, Fenderused exactly those values, and yet the amp did not get way too bassy in later years, they sounded just fine. The only thing increasing the size of the bias filter cap is going to do is reduce the level of hum from ripple in that supply.


Here is the deal, you say ten stupid things, I will call you stupid ten times. You want me not to berate you, then stop posting made up crap.

[pdf64]

My view is that it's fine to relay personal experience even if it runs counter to the accepted norm and you're unable/unwilling to theorize why it might be so, as long as that's clear.
The problem as I see it, with soundguruman's posts, is that occasionally wacky ideas are mixed in with normal good practice, such that it's difficult for someone inexperienced to differentiate, and the wacky ideas might gain status by being associated with normal good practice.
Pete

[soundguruman]

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.

That's 1700 not 17,000

[soundguruman]

My view is that it's fine to relay personal experience even if it runs counter to the accepted norm and you're unable/unwilling to theorize why it might be so, as long as that's clear.
The problem as I see it, with soundguruman's posts, is that occasionally wacky ideas are mixed in with normal good practice, such that it's difficult for someone inexperienced to differentiate, and the wacky ideas might gain status by being associated with normal good practice.
Pete

I am not refusing to explain it. I am merely appalled at the attack nature of the request.
You can label my ideas as wacky. Take it or leave it.

[Steve Conner]

That's 1700 not 17,000

No, you have 1700 posts that appear to be recycled material from the National Enquirer. Enzo has 17,000.

[J M Fahey]

Quote Originally Posted by Steve Conner View Post
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.

That's 1700 not 17,000

Well, this is INCREDIBLE.
Just cutting and pasting from this very same page:

Enzo
Enzo is offline
Senior Member Enzo's Avatar

Join Date
May 2006
Location
Lansing, Michigan, USA
Posts
17,378

How can SGM be SUCH a fool?
Do they give Nobel prizes for that?

Anyway, the main problem is another: people come to this Forum in good faith, trying to solve some problem, but we ere not talking about a "difference of opinion" here, which is healthy, but a SICK making out bad information, for no good purpose, and with even potentially fatal consequences.
At least it destroys credibility in MEF.
Is that the idea?
Well, it is succeeding.

[Steve A.]

My view is that it's fine to relay personal experience even if it runs counter to the accepted norm and you're unable/unwilling to theorize why it might be so, as long as that's clear.

I come up with some really off-the-wall stuff myself. I believe that I was the first person to post the wacky theory that one of Ken Fischer's secrets in his Trainwreck amps was his use of intentional parasitics. But I did identify it as just my own theory based on a few experiments like noticing a big difference in response when reversing the leads of a film and foil coupling cap. (When hooked up "backwards" the amp was a lot more alive. You would normally want the outer foil lead to be connected to the point closer to ground as that tends to reduce parasitics.)

Steve Ahola

[Justin Thomas]

Back to the original thread, can I throw my lot in with "if it ain't broke, don't fix it" crowd?

I'd make it safe first, reasonably reliable second, leave all else alone.

I personally enjoy Enzo & guruman & Juan's posts, but I'm willing to throw in a bigger cap, what the heck... but I can honestly say I never HEARD a difference yet changing a bias cap to a larger value. So was it the original failing, the new tubes, more even bias, what? If a 25uF cap passes down to like 4 Hz, I doubt I'll hear the -68.3Hz that a 75uF cap would make...

Anyway, yeah, leave the amp as original as possible and get it safe & reliable.

Justin

[DrGonz78]

Sorry but I can't help replying about this thread's sub-topic...

I TRY to stay out of the debates between "Everyone" versus "SGM" but I have to note. My first impression on this site between Enzo and SGM... I was trying to revive a Crate amp. Which "Everyone" and "Their Mother's" knows it is one of SGM's favorite amps. So I ask for simple advice regarding a 2050 output transistor that was blown up. I got great advice from "Everyone" but "SGM." SGM's advice "The best advice is to throw it away, not worth putting money into. You can put time money and effort into it, and get it working, then it will fail again for another reason."

Well looking back now I realize just how bad that advice was to anyone that was just learning the very basics of amp repair. Enzo really went at SGM on that thread to say either he help the person fix the amp or get the F out of the way. Enzo said it best on that thread, "It is one things for jerks to show up at a party, but when they start pissing in the punchbowl, it is time to address the issue."

My whole point here is that I want to value every opinion on this website. I want to read all the posts for every diverse bit of information it might contain. Telling someone to not repair an amp, that was easily repairable, is bad advice. This whole site is about experience and advice to all people. I accept that some advice is telling me to not waste time fixing a junky model amp, but that amp got me $25 profit for fixing. The guy I sold the amp to became my first client ever and I have made about $150 working on amps for him. So, how BAD was SGM's advice???

[Enzo]

Thanks Gonz. ANother thing I said to SGM was this: since he loves to claim that Crate stuff will just automatically break, that is cannot be fixed, and whatever you repair today won;t last, and something else will break tomorrow, I challenged him to explain to us just WHAT was wrong about the amps and to explain why they were going to fail. he couldn;t do it.

I don't pick on him just to pick on someone. I really believe if he has worked on amps even a tenth of the time he claims, he probably has some real worthwhile experience to share. Unfortunately it is more important to him to posture and BS the group. I find that sad. And the result is a lot of bogus and flat out wrong advice, and the inexperienced have no way of knowing which is which.


Justin, always glad to get back to topic. The thing is if you put a cap in the signal path, the value does affect freq response. If you fiddle with the cathode bypass caps, that will too. But in the case of the bias supply filter, no signal passes through there at all. It isn't in the signal path. It has one function, smoothing ripple from the bias supply. I guess you could call it a low pass filter, it passes DC and not ripple. Ain't no lower freq than DC.

And that is why I posted a list of bias filter cap values over the years in that model Fender amp. Fender surely didn;t turn it into a bass amp.

[Justin Thomas]

Hey Enzo,

I learned about cap values in a signal path with my Spitfire clone; thanks to Chuck H for making it not sound like pain with my Tele...I just made up the numbers and was being a bit sarcastic about the whole thing. Not too handy with the smileys yet...

I also generally up the bias caps in my amps to 100/100. Haven't had any horrible too-bassy sounds yet. The only time my bias cap made my amp too "bassy" was when the 50/50 in my 67 Bassman crapped out and made lots of HUUUUUMMMMMMMMMMM and redplated my output tubes. One of then was never the same

The bias and filter caps and power cords are the areas to me where reliability and performance trump "vintageness" or "originality." I'm more concerned with "will the amp make it through the gig without killing me or itself?" than collectability. And "mint condition-looking vintage amp" to me says "sounds like crap, I was afraid to play it out."

Just don't drill any holes, and if you DO change any parts, keep them for the next person who might like having the original parts.

Justin

[Steve A.]

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.

I think that you probably want to replace the 10pF cap in the "reverb splitter" RC network with a mica cap. The entire signal from the Vibrato preamp passes through that 10pF cap and parallel 3M3 resistor. You might also want to replace the 3M3 resistor with 2M2 as Mesa Boogie did with some of their early amps.

You might want to try putting in a mica cap for your 250pF treble cap and even try different values- I like 330pF myself (it is easy to experiment with the old Fender amps with the eyelet boards!) I think that a mica treble cap makes the signal clearer.

To measure the capacitance of a cap you need to only disconnect one of the leads, which should be easy enough with an eyelet board. I assume that you do have the more common AB763 version which uses 0.022uF mid caps instead of the 0.033uF in the AA763. I hooked up switches for all of the tone caps on a BF build and the Super Reverb combination of 250pF(mica)/0.1uF/0.022uF(orange drops) really sparkled, almost jumping out at you because it sounded so good. (Most of the other AB763 schematics show a 0.047uF mid cap.) It looks like you have the blue caps which are very similar to Orange Drops (some of the amps back then had ceramic caps in their tone stacks. )

Steve Ahola

[JoeM]

Generally speaking, I don't think ceramics sound bad in these BF amps. And I really don't like going higher with the treble cap, but it's easy enough to experiment with the eyelet boards.

[Steve A.]

Just don't drill any holes...

Awww- that takes all of the FUN out of it!