Kustom K100-2 Pre-amp transistors

[bobsguitars]

A couple weeks ago, I stumbled across a thread about this amp. One of the posts was talking about the pre-amp xsistors needing to be replaced most of the time. I've tried to find that thread again but have failed. Thanks to anyone who can point me in the correct direction.

[52 Bill]

A couple weeks ago, I stumbled across a thread about this amp. One of the posts was talking about the pre-amp xsistors needing to be replaced most of the time. I've tried to find that thread again but have failed. Thanks to anyone who can point me in the correct direction.

Welcome, what problem are you having? I don't seem to recall that these amps need their transistors replaced any more than any other 40 year old amp.

[R.G.]

I don't know the thread, but the schemos for the PC104 and other Kustom amps are here: http://www.vintagekustom.com/literat...h/AmpList.html

The web site seems to be all in a twist about not letting you print them somehow. It almost makes me want to go figure out how to do that anyway.

But I won't. Better judgement triumphs over juvenile pique again.

What transistors were you worried about and why? Older amps often have extremely noisy input transistors because of lack of protection of the input device base emitter from reverse breakage in power on/off and external high voltages. Often replacing the inputs with new/modern ones fixes this.

Perusing the schemo, it looks like there may be issues with the inputs. A quick fix that keeps the degradation from happening at the cost of some high frequency (i.e. few MHz! Not an issue at audio) response is to install a reverse-biased signal diode like a 1N4148 across the base-emitter, cathode to base and anode to emitter (for NPNs, opposite for PNP, of course) especially at the inputs.

[loudthud]

In a couple of threads I looked at, Enzo suggests replacing all the little electrolytic caps.

[J M Fahey]

I'd find the real problem first,repair it, and only then start with embellishments, upgrades and mods.

[gbono]

The last Kustom I worked on had a bad rectifier diode in the low voltage supply - make sure you check the basics before replacing any components.

[bobsguitars]

Thanks for the responses. I replaced the driver t's and 1 o/p t. to get the amp running w/o blowing a fuse. While it's output is healthy in the wattage dept, the wave form is nowhere near a decent looking sine wave-no matter what volume. input signal is good til somewhere around the tone controls. none of the components are numbered, so I'm having a hard time tracing the circuit. Will also check above links to schemos.

[TimmyP1955]

Back when I worked on those, leaky transistors was the most common problem. Of course at that time the caps were brand new, so never a problem there.