Westbury Model 250

Schematic for the Unichord Westbury Model 250 1x12 Combo Amp.

Westbury Model 250

The Westbury line was a Unichord brand of cheap solid state amps. Preamp circuit board was labeled 1979. Note high impedance preamp, perhaps trying to emulate a classic tube preamp. Single trim pot adjusts drain voltage for the third FET. I adjusted this for 1/2V+. Vcc is about +42V, and Vdd is about +33V. Smallest reverb tank I've ever seen - maybe 4 or 5 inches long.

The 0.22Ω emitter resistors in the output section each had about 2.8mV across them. No crossover distortion. Note that the speaker output is out-of-phase with the input. This can be corrected at the speaker terminals.

I serviced a very clean unit that must have received very little use, but was making intermittent horrible noises. Pulling it out, it tested fine, better even, out of the cabinet. Putting it back inside the cabinet, it made its worst noises ever. This was a good thing, as it was a clue as to what was happening. Why would putting it back make a difference? I noticed the cheap chassis had a lot of flex to it, and this in turn flexed the circuit board. I pulled the circuit boards and went after any suspicious solder joints. There were many. After that, the noises appeared to go away. But you never know with intermittent problems.