Gibson GA79 RVT Reverb tank question

[Steve Fundy]

Hello all. New member here, though I have looked here plenty of times for info. So, I am working on a Gibson 79 RVT. The reverb does not function. I have come to the conclusion that the tank is bad. I have return & send working. I have tried subbing different tanks and now have some reverb, but hardly what I would call "lush". I have been trying to locate the correct replacement. No luck. Does anyone have any experience with this amp & perhaps a recommendation for what tank I should get. Additionally the tremolo doesn't work, but that's the next part. I haven't really troubleshot that yet.

Many Thanks
Steve

[shooter]

here's everything start for Gibson;

http://www.0rigami.com/gg/index.html

didn't mention tank type but I got tired reading, good luck

[vampwizzard]

Hello all. New member here, though I have looked here plenty of times for info. So, I am working on a Gibson 79 RVT. The reverb does not function. I have come to the conclusion that the tank is bad. I have return & send working. I have tried subbing different tanks and now have some reverb, but hardly what I would call "lush". I have been trying to locate the correct replacement. No luck. Does anyone have any experience with this amp & perhaps a recommendation for what tank I should get. Additionally the tremolo doesn't work, but that's the next part. I haven't really troubleshot that yet.

Many Thanks
Steve

Which tank did you get? Have you tried a 4fb2a1b?

[sluckey]

According to this schematic...

     https://el34world.com/charts/Schematics/files/Gibson/Gibson_ga79rvt.pdf

the Accutronics 4AB3C1B should work.

[DummyLoad]

the reverb driver transformer may be bad as well as the tank. if the tank input coil failed open, then the driver transformer could have been damaged by flyback due to no load condition.

--pete 

[Steve Fundy]

OK, thanks for the replies. So, @Pete, I put a small test amp on the output of the reverb transformer and it definitely put out sound. As I increase the reverb level it goes up etc. I did also measure the resistance across the secondary and it didn't read as open, but the value was pretty low. When I measured the tank I see 181K ohms on both in & out. Yes, I am a bit baffled by that. I did plug in a tank I had laying around, and a small amount of reverb was produced. That's where my "bad tank" conclusion came from, along with the test of the reverb send. The tubes all tested OK & the return makes a clang if you tap the tank.  Maybe that transformer isn't working properly?

@everyone else, I have found most of those sites etc already. Thanks. I will look at the tank suggestions from both sluckey & vampwizzard.
Thanks all!

[DummyLoad]

odd both coils are bad on that tank. possibly some hard bumps may have caused the sping carrier to hyperextend breaking some very fine wire(s).

--pete

[Steve Fundy]

Hi Pete, the output transducer seems fine as it's quite audible (though not a big crash!) when the springs are bumped. Also, I realized I was in error. The tank measures 181 ohms not 181K. oops! What is really odd, is that both in & out transducers have resistance. Neither is open?

But I did some checking yesterday on the amp itself again yesterday. I rechecked things. I put a test speaker on the verb send & it works. Test tone on return, also works. I measured resistances on resistors & pulled coupling cap out for test, it was OK. Retested & swapped tubes. I tried yet a different reverb tank, one that is very similar in its markings (gibbs 1122 with "C" marking inside) and it makes a very small reverb. That tank came out of a Sano amp. I also tried a different reverb driver transformer with basically identical resistance measurements. No change. I am somewhat baffled. I don't want to buy a replacement tank, and have it not fix the problem.

[sluckey]

The input coil of your tank should read only a couple ohms. The tank I recommended is the tank used by most Fender tube amps. It will work.

[PRR]

> The tank measures 181 ohms

It's a "600 Ohm" tank.

> speaker on the verb send & it works.

Then it is a 6 Ohm send.

You have a 100:1 mis-match. That really hurts power transfer.

Maybe these are "really" 1k or 8 ohms; neither are simple pure resistances. "Close" is good enough. "100 X off" is a poor fit.

[2deaf]

I have a Gibbs tank with a "C" ink stamp and it is the equivalent of a modern 4F tank with a 1.475K input and a 2.25K output.  The story goes that the Gibbs "C" tank was for capacitor driven reverbs and the "F" tank was for Fender style transformer driven reverbs.  Could be because the type "F" is the equivalent of a modern 4A tank with an 8 Ohm input.  Since the GA79 RVT is transformer driven, the tank that sluckey noted would be the appropriate one.

[Steve Fundy]

Thanks all for the help. I have been off this for a few days. I actually went to an actual recording session yesterday, with actual people, in a an actual recording studio! I think the 4AB3c1B is the winner! I got info from a few different sources including sluckey & 2deaf on this forum.
OK Gonna get one & try it.
 

[Steve Fundy]

OK All. Thanks for the info about the reverb problem with this Gibson amp. The reverb is now working. The 4AB3C1B didn't work quite well, but the 4FB3A1A did the trick! Now I am finally ready to tackle the non working trem! Many thanks to all who had pitched in.
Steve

[DummyLoad]

OK All. Thanks for the info about the reverb problem with this Gibson amp. The reverb is now working. The 4AB3C1B didn't work quite well, but the 4FB3A1A did the trick! Now I am finally ready to tackle the non working trem! Many thanks to all who had pitched in.
Steve

very interesting... if that's the case, the secondary of that reverb driver transformer would be/is >8Ω then. perhaps it's a 500-600Ω secondary?


--pete

[2deaf]

Marshall 2210 and 2205 use a transformer and a high impedance tank.  My 2210 came with a 4F tank and the transformer has 4.75T:1T.

The 2205 combo came with a 4D tank.  I didn't document the transformer turns ratio.