12" Polytone guitar amp repair?

[woofcyn]

I have a Polytone guitar amplifier from the early 80s, I think, that needs repair. It makes a very loud, constant sound when turned on even when the volume is turned to the lowest setting. There is no sound from the guitar when plugged in.

What is causing it? Can anyone recommend a repair technician near New York City or the adjacent boroughs?

Thank you.

Photos of the amplifier are here: Woof Cyn's (woofcyn) Library | Photobucket

[52 Bill]

It makes a very loud, constant sound when turned on even when the volume is turned to the lowest setting.

Welcome to the place. With the amp making a loud hum or buzz you should not turn the amp on for any length of time, as it may do damage to the speaker.

The problem that you are describing is usually caused by one of two things. One a bad filter cap or connection, or two a problem with the power amp circuit that is putting a dc voltage on the speaker output.

Try this test. While watching the speaker cone for inward or outward movement, turn on the amp. Does the speaker cone move either in or out and stay there or does it move and then go back to the normal resting position? If the cone does move in or out and stays there, you should not turn the amp on again until you have it looked at. This usually happens when there is an electrical problem with the power amp. The constant dc voltage on the speaker voice coil can cause it to burn out.

If the speaker does not move in or out and stays there, but just hums can be the sign of a bad filter capacitor or at least a bad connection to it. With the amp on try giving the case a good hard hit with your fist. Does jarring the amp cause any change in the noise? If it does, then there is something loose inside the chassis that needs to be tightened or resoldered.

Let us know what you find out.

[oc disorder]

Allow me from Aust ? to recommend a repair shop .. well John from dBm Pro Audio Services
320 West 37th Street, Suite 501 used to post here but I guess being in NYC their rates and overheads are higher
than a shop out in the sticks !

dBm Pro Audio- NYC's Finest Pro Audio, Guitar and Musical Amp, Keyboard, Speaker, and Guitar Repair Center.


EDIT: a tip..make sure all the mounting bolts etc that attach the chassis to the cabinet can be undone easily.
Sometimes it can take longer to get the amp out to fix it than the actual repair itself due to a non co-operative
bolt or screw !!

[woofcyn]

The amp was in very good condition but the power supply was loose and shifting around and caused the wired connection to weaken. I was also too rough and careless during transport. I luckily found a good repairman who fixed it. Thank you for your replies!