VintageKustom.com: Repairing Kustom Amps

Re: Kustom 250-4 [message #27631 is a reply to message #27628]

Sat, 11 January 2020 06:27

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Yes, NTE has discontinued the 725 chip, but I do not think that's where your high frequency distortion is stemming from as channel one and two get mixed together in that chip and then mergered they get sent to the driver board, and more then likely your channel one would be having that same issue.
What I would do next is unplug, clean and then replug in all the interboard connectors a few times to is if first that fixes it.
Be careful with the plug on the power amp driver board as I have had a few amps who's pins on that board where barely soldered in on the bottom side.

Check to see if you can rock them at all.

If the connector removing and cleaning does not fix the issue then I would look at replacing all the small Tantalum electrolytic caps on that board as one of them is likely partitaly shiorted and dropping down the needed +12 or -12 volts that powers that board.

I would therefore replace C6 and C7 on that preamp board ( 100uf 15 volt) with non polarized filter caps with a 25 volt or better rating, in fact if it where me then while I was in there I would replace all of these type caps on all the boards since they are all the same age and don't last forever!

Just be sure to work on one board at a time so that if you make a mistake you will have not screwed yourself as bad!

Also be darn sure to not turn the amp on without the connector on the driver board plugged in as that will damage the output stage.
Let us know how things go.

[Updated on: Sat, 11 January 2020 06:37]

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