1963 Gibson Hawk 2x10 Ga25 RVT

[Songwriter]

I have a 1963 Hawk. Recently it seems to have lost volume, I can crank it up and just doesn't get loud and there is sort of a metal sonding vibration coming out of it. I was told to try changing the power tubes which are two 7591 tubes.Does that sound like it could be the problem?

Also does anyone know what type speakers are in these models, they have a square base...

[olddawg]

I have a 1963 Hawk. Recently it seems to have lost volume, I can crank it up and just doesn't get loud and there is sort of a metal sonding vibration coming out of it. I was told to try changing the power tubes which are two 7591 tubes.Does that sound like it could be the problem?

Also does anyone know what type speakers are in these models, they have a square base...

If the magnets themselves are square it usually means a CTS. If it a squarish metal enclosure around a cylindrical magnet it is probably a Jensen.

Output tubes can cause your problem but so can other things like capacitors. How old are the tubes?

[Songwriter]

1963 Gibson Hawk

Not really sure how old. I bought it about 4-5 years ago and when I had it checked out they said hte tubes were good. It jsut started losing power and the vibration sound a few days ago... They could be five years old or 35 years old. I know some of them are barely readable...

[olddawg]

Not really sure how old. I bought it about 4-5 years ago and when I had it checked out they said hte tubes were good. It jsut started losing power and the vibration sound a few days ago... They could be five years old or 35 years old. I know some of them are barely readable...

If you use the amp regularly, 5 years is a long life for tubes. I would start with replacing the output tubes. You should always have a backup set anyway. Tubes are very mechanical and can fail at any time. For a 45+ year old amp you probably also have some failing caps, especially filter caps. Even if you don't have hum you could have attenuated base response which can be percieved as a loss of gain. I would recommend a re-tube and re-cap if it is not a total museum piece. If it hasn't been used a lot the original pre tubes might be fine. Hell, the outputs might be fine if it hasn't been used much and just the caps bad. Hard to tell without looking at it. There are exceptions. I have a '63 Fender Tremolux (w/ two originl 2X10 cabs) that is bone stock. The only thing that has ever been done to it is replacement of the 6L6GCs.

[dkevin]

Ga-25rvt

I have a GA-25RVT too. Is there any way you can test the tubes or have them tested to verify their strength? The repair process can become quite confusing (not to mention expensive) if you are throwing money at new tubes.
The way you describe the suddenness of the volume drop makes me think you might have lost a cathode bypass capacitor (or two). If you have a schematic, and have some repair savvy, try patching a "known good/new" bypass capacitor over the cathode resistor. Also, the schematic can help you use a multimeter to test the cathode and plate voltages of each tube.
Your problem may prove to be the output tubes but it is equally as likely (and much less costly) that another component is faulty.
dkevin