1965 Gibson GR25rvt Hawk

[jnl636]

Anyone know the tube layout for this amp? There might be one in wrong. All I get is a very loud hum no matter where the volume controls are at. Uses 7191's in the output.

[Swarty]

99% probability of bad filter caps. I've worked on a bzillion Gibsons, those dual cigar shaped filters just didn't hold up.

[lexluther]

V1 6eu7,v2 12au7,v3 6eu7,v4 12au7,v5&6 7591 v7 12au7. There were 3 or 4 different schematics for the same Amp. Gibson was horrible about this. It shows on my epiphone schematic for a ea15rvt this tube chart. They were supposed to be the same amp. I subed for the driver tube v4 a 12at7 which made the amp sound much better IMO. A 12ax7 would work but broke up sooner. These amps tended to sound very clean. if you have an oa2 in the circuit then this chart isn't right!!!

[jnl636]

It’s a 1965. Ok bad hum when turned on. Lower freq than 60hz.Replaced the filter caps 20mf @ 400 (Big Brown things) with 22uf @500 Tech caps. Tied negatives together to BLK and ran 2 positives to reds. Did on all 3 caps.
Still have hum. Replaced outputs because I had a pair. Still hum. Can remove all tubes except the outputs and still have hum. Controls have no affect. Please help.
V1= 6EU7 V2= 12AU7 V3= 6EU7 V4= 12AU7 V5 & V6= 7591 V7=12AU7 No rectifier tube. Some people say it more resembles a GS-35RVT. No audio I can pull all the tube except the outputs and will still get hum (motor boating sound).

[lexluther]

Is that the location your tube's were installed before my email? As i said there were alot of different schematics by gibson. If its correct i have the schematics. My EA r15rvt epiphone schematics say its the same with exceptions noted as a Ga 25rvt. I could send them in pdf form.

[jnl636]

From what I understand this is the correct lay out. Still doesn't help me with the motorboating.

[lexluther]

There are 4 x 20mfd and 1x40mfd caps in the power supply area. You may have missed a few according to my schematic. Also the amp has and interstage tranny. Are you getting any audio passing through? How are your voltages at the supply? Is the tremolo off?