Reverb Tank question...

[5thumbs]

I have been using Accutronics tanks for my amp builds and switched over to the Korean version when the US ones were discontinued. Anyway, I was reading comparisons of the different brand tanks and read that the MOD tank was a little more pronounced in it's reverb output. I wanted to give my reverb a wide sweep from dry to surf and so i though i would give the MODs a try. I am using the 8AB2A1B 3-spring short tank Accutronics and bought 2 of the MOD equivalents. When I plug either of the 2 MODs I purchased into my circuit there is hardly any reverb effect at all. I have to dime the knob to get any effect. Measuring the resistance (out of circuit) at the input and output plugs I get: Accutronics - 1.2ohm at input, 220ohm at output, MOD 30ohm at input, 220ohm at output. Is this input resistance attenuating my reverb signal and causing the weak output with the MOD tank? If I keep these tanks, would I go to a lower reverb potentiometer or lower the resistance in the reverb circuit? Anyone else dealt with this issue? Thanks for all your help!

Tim

[52 Bill]

I am using the 8AB2A1B 3-spring short tank Accutronics and bought 2 of the MOD equivalents.

The MOD tanks are not the same, the input transducer is too high of an impedance to work correctly with the drive circuit of you amp. Return them and get the correct tanks.

[5thumbs]

Thanks Bill for the reply. The MOD tanks have the same part numbers as the Accutronics, but they must have gotten mis-labeled :-( or maybe they are not direct replacements.

Thanks again for your help,
Tim

[g1]

The Mod tanks should be direct replacements for Accutronics, same numbering system. Likely they were mis-labeled as you mentioned.
At the input, 25ohm resistance (approx.) would be type B, 30ohm type C.
A search for 8CB2A1B comes up blank, but 8BB2A1B shows as being used in SLM amps, so I would suspect that is what you have.
Starting at the bottom of page 8 of the pdf attached is the Accutronics and Mod numbering system. Page 9 lists the impedances with approx. DC resistance readings.

[5thumbs]

Thanks for all your help. CE Distribution is sending a RA # for me to return these tanks for the correct ones. So they definitely were mis-labeled.

So anyone having issues with their reverb circuits, be aware that the MOD tank you think you have may not actually be the correct tank! ;-)

[Tom Phillips]

... I wanted to give my reverb a wide sweep from dry to surf ...

Tim,
If you have room to install a full size (Long) tank then maybe this is an opportunity to upgrade since you are doing a return anyway. I think a long tank will give you a better surf sound than a short tank and it can still be turned down to dry.
Something to consider anyway.
Tom