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reverb tanks, differences?

5/1/2006 4:18 PM
Ian Anderson
reverb tanks, differences?
ok, the reverb tank is gone in my Ampeg VL-1002 head & I need a replacement BUT I don't know the spec - how do I choose the correct replacement? (this is the first time I've dealt with reverb in an amp)  
I've been looking at the replacements available 'here' but they all look the same except for whether they're long/short tanks or two/three springs.  
I need some help here (argh!)  
Thanks... Ian
5/1/2006 6:37 PM

Is it missing or just bad? On the pan there will be a number like 4AB3C1B. That number is what you want to order. If you don't have the pan to find out, get the one in my example.  
Antique Electronic Supply sells them for $22.95, so you could save a few bucks over the source you found.
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5/2/2006 6:05 AM
Ian Anderson

Enzo, the spring has snapped at one end and looks pretty much unrepairable. Its not an accutronics tank, it's marked with a 'BT' logo on the side and the model# 79-214-02 on the top of the tank. (edit)... just had a look at the TubesAndMore site, looks like I have a Belton reverb tank. Are there other tanks that are considered an upgrade? - I'm willing to spend a little extra here if necessary.  
Could you briefly explain the differences between tanks - how does the number of springs affect the tone of the reverb (if at all). Is the long versus short tank simply a matter of decay time?  
Cheers... Ian
5/2/2006 9:07 AM
Mark Hammer

Tanks are spec'd for different input and output impedances. I can't think of any reason why one impedance would sound "better" than another. I can think of several reasons, however, why using a tank that was a mismatch to the impedances the amp itself expects to see might not sound that great, so it is best to use something that either conforms well to the impedance specs of the original, or else find a way to "mate" the driver stage of the amp to the input of the tank a little better (there is usually much less mismatch between tanks and recovery amp) such as with a matching transformer.  
In general, having longer springs results in longer initial reflection times and greater duration of reverb sound. Remember that the vibrations travel back and forth along the spring, just like splashing in the bathtub produces ripples that go from one end to the other, back and forth. Greater distances mean that the same number of back and forths takes longer.  
In general, having more springs results in a sound which is less seemingly resonant because it is more multi-resonant. Huh? All springs, as mechanical devices, play up certain resonances. Because no two springs are exactly alike, and because the springs selected for multi-spring units are chosen to be a little different, there are enough diverse resonances introduced that the tone is not focussed on any particular one. People describe it as sounding richer. The difference between a single short spring and multiple longer springs is a bit like the different between the highly resonant reverb you find in a stairwell or tiled high-school bathroom, versus the reverb you would find in a large hall in an art museum with lots of objects and people to break up standing waves. Springs obviously won't sound as good as that hall, but 3 long ones will move you more in that direction.  
My limited experience with spring reverbs has been that not a lot of thought seems to go into the tone of the support electronics in the amp. In the late 80's I picked up a medium-power SS Gibson combo amp (only had it briefly, so I don't remember the model) that had a simply awful reverb tone. The redeeming unusual feature seemed to be that the reverb return entered the signal path after the volume control such that you could have an all reverb signal (??? Yep) but good lord did that thing honk! I traced the circuit and found the series cap leading to the input of the reverb pan. I replaced it with a much smaller value such that the bass was chopped from what was sent to the pan, and the reverb tone improved 100%, from toilet-tone to "air".
5/2/2006 9:40 AM
Ian Anderson

"(snip) I can think of several reasons why using a tank that was a mismatch to the impedances the amp itself expects to see might not sound that great, so it is best to use something that either conforms well to the impedance specs of the original. "
thanks for the reply Mark, can you elaborate on the effect of lower/higher input/output impedences with respect to the overall tone of the amp.  
my problem here is that I can't seem to find any info on the actual reverb tank in my amp, therefore choosing a replacement is that bit harder.  
... Ian
5/2/2006 1:37 PM
Man o'Blues
Your best bet is to contact Ampeg (they're still around, aren't they?) and ask what type replacement tank it takes.  
A quick peek at the preamp schematic shows that it's a tranny driven reverb circuit. The driver tube is a indicated as 9-pin miniature and the same part no. as all of the other preamp tubes. Since the schemo is fairly recent('91), I'd guess the driver is a 12AX7. So it's *probably* a low-ish impedance tank, depending on the tranny specs. But again, find out from the manufacturer to be on the safe side.
5/2/2006 12:28 PM

The transformers on the unit are color coded for impedence. you need to match up input and output. Call antique electronics for assistance at 1-480-820-5411. Have the pan in your hands when you call. The manufacturer is Vibroworld but they are apparently moving and not taking orders.
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