'61 Gibson Falcon GA19RVT Reverb buzz

[UnexplodedCow]

I've dealt with this for a long time, and haven't used the amp in a while. I never took it to a tech due to cost or the fact that I like working on things myself.

 

The amp in question is a '61 Tweed Gibson Falcon, model GA19RVT. Not a common amp, though the circuit schematic is abundant over the internet. It's the model that uses the 7199 for the reverb driver.

 

The only issue I've had is a horrendous buzz in the reverb circuit. It wasn't working previously, and I fixed that (footpedal wiring issue). The buzz happens when the reverb circuit is engaged, and the amp is otherwise silent. I also noticed at high reverb settings I have more gain in the circuit, and the reverb itself can cause a little bit of sound to come out of the amp with the main volume down to 0. I can't remember if that is normal for this amp or not (it's a bit different than the typical Fender/Marshall stuff).

 

I'll look into a loose ground today, and need to get a replacement 7199, but other than that, any suggestions? The tank tests fine (long tail 3 spring accutronics), and the reverb does sound really, really deep and echoey, but has the buzz that is about as loud as the guitar.

 

I also need to give it some new power tubes...getting flourescence out of them (one more than the other) the bright blue on the glass kind.

 

Below is the schematic, and thanks for any help/suggestions.

 

http://elektrotanya.com/PREVIEWS/63463243/23432455/gibson/gibson_ga-19rvt_schematic.pdf_1.png

[SamBooka]

I've dealt with this for a long time, and haven't used the amp in a while. I never took it to a tech due to cost or the fact that I like working on things myself.

 

The amp in question is a '61 Tweed Gibson Falcon, model GA19RVT. Not a common amp, though the circuit schematic is abundant over the internet. It's the model that uses the 7199 for the reverb driver.

 

The only issue I've had is a horrendous buzz in the reverb circuit. It wasn't working previously, and I fixed that (footpedal wiring issue). The buzz happens when the reverb circuit is engaged, and the amp is otherwise silent. I also noticed at high reverb settings I have more gain in the circuit, and the reverb itself can cause a little bit of sound to come out of the amp with the main volume down to 0. I can't remember if that is normal for this amp or not (it's a bit different than the typical Fender/Marshall stuff).

 

I'll look into a loose ground today, and need to get a replacement 7199, but other than that, any suggestions? The tank tests fine (long tail 3 spring accutronics), and the reverb does sound really, really deep and echoey, but has the buzz that is about as loud as the guitar.

 

I also need to give it some new power tubes...getting flourescence out of them (one more than the other) the bright blue on the glass kind.

 

Below is the schematic, and thanks for any help/suggestions.

 

http://elektrotanya.com/PREVIEWS/63463243/23432455/gibson/gibson_ga-19rvt_schematic.pdf_1.png

 

Bright blue isnt a problem for power tubes.. better tests are checking the bias and plate voltages.

If nothing has been done to the amp then the filter caps in the power supply are probably in need of replacing.

 

None of that has to do with your reverb issue. I am not quite clear from your description but if the reverb ctl is at 0 (not the FS but the control pot) is the noise there?

[UnexplodedCow]

Bright blue isnt a problem for power tubes.. better tests are checking the bias and plate voltages.

If nothing has been done to the amp then the filter caps in the power supply are probably in need of replacing.

 

None of that has to do with your reverb issue. I am not quite clear from your description but if the reverb ctl is at 0 (not the FS but the control pot) is the noise there?

 

If the reverb is at 0 with the circuit engaged (switch closed) then there is a buzz, but it will get louder as the reverb pot is turned clockwise (to increase reverb level). If the circuit is disengaged (switch open) then the noise is not there, and the amp is perfectly quiet (no hum, buzz, hiss, etc.) and will be fine even at higher volumes. Yes, the filter caps likely need replacement, but that's another project for the future, as I'm trying to get it a bit more solid, and then improve things as necessary. Also, bias is fixed, and I have not tested it, but it has never given me a reason to in the past (used this amp for years before putting it away with the buzz).

 

Thanks for the reply!

[retrorod]

I would double-check the reverb cables for ground issues, especially the RCA jacks. Check and clean the jacks where they connect to the tank itself. Check the connections and components associated with V2(7199) socket also.

Does the reverb tank operate buzz-free when plugged in to another amp?

[UnexplodedCow]

I would double-check the reverb cables for ground issues, especially the RCA jacks. Check and clean the jacks where they connect to the tank itself. Check the connections and components associated with V2(7199) socket also.

Does the reverb tank operate buzz-free when plugged in to another amp?

 

I was thinking of checking the RCA lines themselves since they are old and a bit inflexible. The connectors themselves are clean, as are the tank connectors. I've tried another (appropriate resistance) reverb tank and the same buzz results, so it's not the tank. The spare tank is known to be good. I have not yet tried the tank in another amp as I didn't have one with reverb at the time (I do now). I have not found any obviously dead components. The tube socket and tube connectors were cleaned years ago, before the amp sat covered up in a closet, and they looked clean when I checked the tube the other day. I'm wondering if the reverb pot itself has a leak, or if a capacitor failed and became conductive. I don't believe it's the footswitch anymore, but will try bypassing it to see if it will resolve the buzz.

 

I appreciate the help.