Sunday, September 12, 2010

Amp Supply Company LK-500ZC Rebuild

This project started when I lost a blocking cap on the B+ and it smoked the plate choke.  I have owned the amp for a few years now and knew it had some issues.  The ALO circuit had problems and was bypassed, the fan speed control circuit was not working, and the plate tuning cap had been arced badly and ground down.

With the ALO bypassed I only had plate voltage metering and no current metering at all.  I think the problem with the ALO is a burned resistor that is used as a shunt for the sensing circuit.  This makes tune up a questionable process, but with the forgiving nature of 3-500Z Eimacs I used the amp anyway.  The fan speed was controlled by a light dimmer I installed on the rear to vary the speed of the fan.  I am uncertain of why the original fan speed circuit was bypassed and the switch for high/low was missing.

During dis-assembly I noticed the band switch had the 15m possition burned.  I guess it's a good thing I never used the amp for 15m!

I have removed all components from the chassis and cleaned it. 

I have ordered new blocking caps and installed them along with the new plate choke.

And the new E.F. Johnson Plate tuning cap.
The stem is longer than needed for this amp and I will have to cut it down.

More to come as the project progresses....................................