VintageKustom.com: Repairing Kustom Amps

Tue, 18 January 2022 16:27

TelesnTubes
Messages: 2
Registered: January 2022

Junior Member

Hello

I am new here. Thanks for sharing so much info on Kustom amps. I am a tube amp guy trying to navigate my fist solid state amp repair. It is a Kustom 150-1 head. Amp is not passing audio and has an audible hum thru my 8ohm test speaker. I have removed the signal input wiring harness plug to see if the problem is in the pre amp or power section. There was no change. So I suspect an issue in the PC5033 power amp board. I have 46 +/- VDC on the big filter caps and 12 +/- on the terminal block and wiring to the preamp boards. I also read 15 VDC on the speaker jack - my experience with tube amps tells me there should not be DC on the speaker output and maybe there is a coupling capacitor that is bad.

I have not started measuring/testing components or voltage at each component yet. I wanted to see if I am on the right track or should I start elsewhere? I also have a question about the correct value for C4. The schematic says 33uf. I wonder if the decimal point is missing and if the correct value is .33uf or 3.3uf. I can't see the code on the capacitor. I have found most of the transistors online except for the 40408/nte190. What is an equivalent for this transistor. I also see the IC and suggested nte725 replacement are obsolete. Any suggestions if these need to be replaced? I hope the issue is contained to the PC5033 board.

Thanks!

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