VintageKustom.com: Repairing Kustom Amps » Kustom K100 2 - Just Hum/Buzz

Re: Kustom K100 2 - Just Hum/Buzz - No Other sound [message #23184 is a reply to message #23183]

Tue, 23 June 2015 15:18

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

Jameson, welcome to the place.

Assuming that you have the basic skill set to know that working on a live amp can kill you, start by thinking what is wrong with the amp, rather than what can I replace.

If there is a constant hum that is not affected by any of the controls, then you should look at the power supply. Take your voltmeter and begin tests by reading the voltage across the speaker jack (no speaker plugged in). Read dc and ac voltages. The closer to zero in both readings is best. What do you get?

If there is any more than a volt do not plug a speaker back into the amp until you have resolved this problem as it could do damage to the speaker and could do additional harm to the amp.

Next step is to test the +&- power supplies. If you go to the technical section of this site, you can look up the schematic for this amp. The two main power supplies are about +&- 40 volts dc. On the pc board there are two large filter caps. I think that they are rated 2500uF @ 50 volts. Read the ac and dc voltage directly across each cap. What voltage readings do you get?

Check to be certain that these caps are solidly soldered in. Report back what you find out in your testing.

Edit: I just checked the schematic, the main filter caps are not mounted on the pc board, but the tests remain the same. Also be sure that the connection screws are clean and tight.

[Updated on: Tue, 23 June 2015 15:31]

Report message to a moderator