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Post subject: What type of replacement reverb for Red Knob Evil Twin?
Posted: Wed Mar 18, 2015 11:19 pm
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Joined: Wed Mar 18, 2015 11:14 pm
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Hi,

I've owned my red knob evil twin since the late 80s, or maybe it was 1990??

I think I have to replace the spring reverb tank - at first it started feeding back only when set to a very high value but now it's feeding back even when set to a low value like 4.

First off: Would there be any other reason for this other than a broken down reverb tank?

Secondly: What is the correct reverb tank type to get for this amp?

Based on what I can tell from visually inspecting the existing unit it would be one of the following two perhaps??

4AB3C1B Reverb Tank, Accutronics
Input Impedance 8 Ohms, Output Impedance 2250 Ohms

4EB3C1B Reverb Tank, Accutronics
Input Impedance 600 Ohms, Output Impedance 2250 Ohms


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Post subject: Re: What type of replacement reverb for Red Knob Evil Twin?
Posted: Thu Mar 19, 2015 2:10 am
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Joined: Tue Jun 29, 2010 1:20 pm
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Location: Indiana
Hi JosephEx,

First, have you tried replacing the reverb driver tube, 12AT7, or the reverb recovery tube, 12AX7? It sounds more like a tube issue to me.

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Post subject: Re: What type of replacement reverb for Red Knob Evil Twin?
Posted: Fri Mar 20, 2015 12:16 pm
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I agree it could just be a tube issue. I just built an outboard reverb unit and one of the tubes shipped was bad and not only did it not work properly, but it messed with some voltages. I just build amps and stuff and just make sure everything's within the recommended voltages, Arjay, Shimmy, stratele and others are the real tech guys. Any way you look at at tanks and preamp tubes are cheap unless you go NOS. I highly recommend NOS for the 12AT7. The JJ I had was pretty noisy so I replaced it with a NOS JAN Phillips. Modkits DIY also make some nice, high quality reverb tanks if you need one.

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