Re: Blackface a Silverface Super Reverb



Ether wrote:

Rich Koerner wrote:
Ether wrote:

<SNIP>


I'm going to have to work up a page on the Super Reverb for my web site down the road.

Not mentioning what SF version is at hand is a problem.

If you have the 70 watt SF Super Reverb.... boy do you have your work cut out for you.

However, setting up of those babies in the right fashion makes for a very KILLER Super Reverb.

You mean, adding a choke, disconnecting the UL taps, changing the PT,
etc., etc.?

Correct.

Not worth it. Unless you're willing to do the work for
free!

You'll change your mind once you experienced it.

You'd be better off putting the money into an amp that designed the
way you want--and saving the effort.


How would the uneducated musician in amplifier design, have basis to make an informed decision on
such?

You are expert on amp design?




<thinking>

For now, let me keep thing in a general context, for the sake of BF and early SF perspective, and
awareness.

From 1964 to 1969, in speakers alone, there are noticeable differences in the many different
speakers that Fender shipped in their Super Reverbs.

Of those, the alnico and the many ceramics, which is your base reference point for the targeted
standard?

Not all these speakers sounded the same. Personally, one of the ceramic swiss cheese framed 10's
were their best.

The alnicos are pretty good, too.

However, that is just a me thing.

There were also the transformer changes the went along the way in the time line too. Voltage
differences and current draw limits make for differences in a Super Reverb's performance too. These
little things make the differences when compared side by side.

The voltage differences between BF and SF are the bigger issue. The SF
PT's have higher secondary voltages, so if you try to put a 5AR4 or
diodes in a SFSR, the B+ voltage winds up being way too high, and the
amps sounds brittle.

High voltage on tubes run too cold causes what I believe you are talking about.

High voltage--period--is the problem, regardless of bias.

Where the hell did this notion that high voltage is any kind of problem associated with poor
performance.

Think in terms of a high order of performance magnitude, and the error in this thinking can be
found.



Did you read
Jim's comments on the JCM vs. JMP 800? The amp with the lower plate
voltage will have the sweeter tone.

Well, any time you want to achieve low performance from a high performance design, you can arrive at
such a conclusion because of the error in thinking behind the exercise.



Bias by numbers guys always have that problem.

I always trust my ears.


But, this leads to the present conclusions in error.





Not to mention that the other voltages in the amp
will be high, too.

Which, is not a problem to correct.

Just an unnecessary pain in the ass. And if the plate voltage is too
high, it doesn't matter much what's going on in the preamp stages. The
tone is going to suck regardless.


WRONG!





The differences in current supply from the BF and
SF PT's aren't that big a deal. Yeah, the 5AR4 sounds great in a
BFSR, but if you've got a SFSR, you're best off keeping the 5U4 in
there.


Not an always absolute.

Pretty much!

Which, depends on the exact targeted Super Reverb results of the owner/user.

Unless the owner likes the hard and sterile tone caused by the high
plate voltage, you're out of luck.

Again, a conclusion in error.

Here are the specs common to those tubes used in amp design.

http://www.timeelect.com/6550ap1.gif
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This tube data represents what the vacuum actually does.

Point out the *tone suck points* you are talking about on the operating curves supplied, and I'll
show you a tube/s performing at improper operating points.

High voltage is NOT the cause for bad tone.

Improper tube operation and/or application IS.



Then, there are the other equally fine points that are most often glossed over as not being that
important for consideration in the SF to BF conversions.

What it all boils down to is, the exact voltages, on the exact tubes, so the exact speakers, with a
power supply response characteristic, with the properly referenced EQ within the different stages of
the Super Reverb. Or, any other amplifier where a similar goal if the point of the quest.

What is omitted from the four points of focus depends on much detail you want to get into. For most
these four points is all it takes. For others, close is not good enough.

If you are one of those cats, you have to have a clearly defined target. Then, the small details
become the things that you have to jump on.

First the exact tubes and speakers are a must.

The proper voltages from the power supply's divider string has to be addressed. Those rascals
changed in the time line.

Yeah, but--That's usually not that big a deal, either--especially
compared to the controlling the plate and B+ voltage coming from the
rectifier. Often, you find SF amps with the old BF power ladder
resistor values anyway.

Yet, this is not addressed by many as an important point of focus. But it is if you want to have
the Super Reverb that makes the difference in performance other don't achieve.

All else being equal, yes. But like I said, if the output tube plate
voltage is too high, tweaking the preamp voltages is pointless.


You really lack the understanding on how the vacuum tube really works.




Depending on the transformers sitting in your SF, you either can use the
stock resistor string, or have to calculate new values to get all the voltages to each of the stages
to the proper targeted BF values.

The SF preamp voltages produce some nice tones, too, so I wouldn't
worry about that right away as part of a BF conversion. The phase
inverter changes are often all you need for great sound.

Then, just looking into the time line changes to the reverb alone, is an important consideration
too. If the tank isn't driven right, the reverb isn't going to sound right. The big plate NOS 12AT7
is a nice thing to have in that socket to drive the reverb tank with a 2.2K kathode resistor.

Yeah, good tubes often make a bigger difference than pretty much
anything else. Shitty tubes can make a BF amp sound like crap.


On the way back, make sure all the caps are the right BF values too.

Especially the PI coupling cap. Though the higher .01uF SF coupling
cap sounds bigger, though it passes too much bass at higher volumes.

Turn down the bass control. That's what they are there for.

Not the same thing. You can't achieve the same tonal characteristics
when the PI coupling cap value is off by a factor of ten. Play a BFSR
and SFSR side by side--you'll see what I mean.

In the example of too much bass, the type of filter (fixed or variable), or where it's located,
still performs the same function.





Depending on the type of by-pass and coupling caps that sit in the subject SF Super Reverb, few to
all may need replacing because of value changes.

Those things are far more durable than you would expect, even after
30-40 years.

I don't care how old they are. I measure 'em all. If they are off value, they are out of the amp.

If they're out of spec--sure. But that's rarer than you'd think--even
on a decades-old amp.

Not by my experience.

How many kathode caps have you measured from the amps of long ago still on spec?

http://www.timeelect.com/eh-150.htm

http://www.timeelect.com/vinfpa.htm

http://www.timeelect.com/vinchamp.htm

http://www.timeelect.com/concert.htm

Coupling caps too.

ALL of the caps from the old days age and drift.

Like I said. I measure 'em all. If they are off value, they are out of the amp.

Depending on the type of cap, the value, type of circuit they are in.... temperature is also a
factor in drift.

Did you know that?


Slap both bias adj and bal into the amp.

If you don't mind fiddling with that. As long as you use closely
matched tubes, the bias adjust control is all you really need.

Not if you want to feed the amp Polished Turds.

A lot of new tubes suck. But a lot of new tubes can also be bought
closely matched--and stay that way. No great need for a balance
control.



Well, if what you are saying is absolutely true... why have an adjustable bias control at all.

These tubes today that you say are manufactured so perfectly to stay MATCHED... they should all
therefore have equally a matched starting points in their life time too. RIGHT?

So, there is no need for ANY bias adjustments or re-adjustments EVER!

But then, there is the common mistaking notion that, it is the bias supply itself, that is the REAL
cause of any tube drifting problem in the equation.




I like the AB763 PI ckt.

Much preferred.


I'd use only the 5AR4. (I use SI diodes in mine)

Not an option with most SF amps. The B+ voltage winds up being too
high.

Too high? Well, I guess I never saw it as a problem of any kind.

Not if you like hard, sterile tone. I guess some people ain't that
particular!


There is nothing sterile of hard sounding about an Ampeg VT-40.

Yet, there is 600 volts on the plates of the two 7027 tubes in that amp.

Didn't know that, did ya.



Then, there is nothing hard and sterile about a well set-up 1971 Super Lead with 535 volts B+
sitting on the plates of some nice Mullard EL-34's running on the warm side.

But, what you are going to object to is the FACT that, this amp is a HIGH PERFORMANCE *STAGE* AMP
and is over kill for your common bedroom, garage, and small club venues.

Using this 1971 Marshall JMP at the LOWER desired volume levels, you are naturally going to conclude
in error that, this great sounding HIGH PERFORMANCE *STAGE* AMP is now hard and sterile sounding
because of it's high voltage.

It's kind a like using a top fuel dragster to go food shopping and complaining about snapping your
neck every time you touch the gas pedal, having concluded that too much nitro entering the engine is
the problem.


Also,... GE, Sylvania, or RCA for tubes.

Well, that goes without saying! Telefunken, Mullard, and Amperex will
do in a pinch.


After this is done, the suppression caps are pulled, and lead dress is the final move.

Many of the SF amps--at least earlier ones--don't really need lead
dress adjustment, but it can't hurt. Some of the later 70s amps are a
mess.


If I gave this more thought, I may find some things to add I may have forgotten in the throw
together post.

You forgot about adding a dash of mojo. Doesn't sound the same without
it.

Actually, I rip out the boost ckt, and leave the master volume ckt in most of the Super Reverbs that
leave the shop.

Not a big deal. Having an MV pot in there is much less of an evil than
having B+ that's 100V too high.

--E




Regards,

Rich Koerner,
Time Electronics.
http://www.timeelect.com

Specialists in Live Sound FOH Engineering,
Music & Studio Production,
Vintage Instruments, and Tube Amplifiers
.

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