Tube Amps / Music Electronics
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|2/25/2005 4:26 AM|
||Gibson reverb question|
Hi all, can anyone tell me what the input and output impedance should be for a Gibson GA-17RVT amp's reverb tank? So far I have not been sucessful in getting the reverb to work properly.The old tank is shot, missing the transducer at one end, and with a standard Fender tank I'm getting very minimal, minute reverb effect.
Any help will be greatly appreciated.
|2/25/2005 9:34 AM|
I sent you an email, but for the benefit of everyone else I'll post here too. I contacted Cal from Accutronics and he helped me out with my reverb problem on my '60s GA-19RVT. I was getting ~175ohms at the input and output on my tank (simple R reading w/ DVM) and Cal said that sounded typical for a 60's reverb tank.
He pointed me to the 4FB2A1B as a replacement, saying I could also use a 4FB3A1B (longer delay time). I haven't received it yet to try out, but I can let you know how it works out.
|2/25/2005 12:47 PM|
Typical transformer drive circuits like this used a very low input impedance. I know I have subbed a fender drive transformer and 4AB3C1B tank in Gibson amps with good results. There are many possible reasons why your reverb may be weak - bad cathode caps, drive transformer, tube, tank not properly terminated for your application etc..
A tank with an input resistance of 175+ ohms is usually only found in units with a solid state driver.
You may need to measure the drive transformer with some signals and a DVM to determine it's turns ratio.
|2/26/2005 12:51 AM|
Thanks Alex and Rick,
Alex: I have been trying a 4bb3c1b-not working properly, I think this is a fender pan.
Rick: reverb tube is good, and new cathode caps are installed, along with electrolytics and new cord.
I can get a heck of a crash out of the amp if I bump the pan but not much guitar signal is effected. The input measured 26 Ohms and 212 Ohms output of that pan I have been trying. I love the tremelo this amp has, I just need to get the reverb going.
What could I check on the reverb output transformer?
Also, would it make any differenc if the secondaries were swithced on this transformenr? I think someone had messed with it before I got the amp.
|3/2/2005 7:04 AM|
I got the 4FB2A1B tank in the mail and tried it out. The reverb was extremely weak, so I don't think this was the correct replacement. I'm not sure where to go from here.
Anyone have any suggestions?
|3/3/2005 4:21 AM|
How does your circuit check-out before and after your reverb in the amp? I traced my reverb and found someone had swapped out a resistor for a lowr value, 1/2 of what it should have been!!! according to the schematic. Did you also change your cathode bypass caps on your reverb tubes?
|3/3/2005 8:31 AM|
What's weird is the reverb sounds really good with my old tank even though one of the springs is broken. I just recently got this amp, so I was checking everything out and discovered the broken spring.
I haven't changed out the cathode bypass caps on any of the preamp tubes or the reverb driver (I've heard it's a good idea though). The amp actually sounds really good with the old tank (I put in a reverb mix control to reduce the noise due to the reverb channel) but I was curious if it would get better w/ a fixed tank. All the components look original in the amp.
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