The Churchill PA Power Amplifier and Power Supply
The modular power amp used in the Churchill PA also powered the Super Beatle / Beatle series of amps and the V1182 Westminster Bass. In addition to the power amp circuit, the DC power supply for the amp was also a part of this module. See an image of the Churchill / Beatle / Westminster modular power amp module below.
The power supply circuit starts at the 120 VAC front panel rotary power switch. From the power switch, the line voltage flows through cables and a nine pin connector to the power transformer, located on the power amp module. A grounded aluminum panel shielded the mixer module from hum producing fields eminating from the transformer.
The single tap power transformer dropped the 120 VAC line voltage to about 40 VAC. A full wave diode bridge and twin 5000 uf smoothing filter capacitors provided +31 VDC and -31 VDC voltages to supply the power amp circuit. 27 VDC, 18 VDC and 14 VDC power taps were created through the use of additional filter capacitors and dropping resistors in the power supply. The 18 and 14 VDC supply voltages powered the mixer module.
The output section of the Churchill was originally designed to be an OTL (output transformerless) solid state power amp circuit rated at 120 watts RMS, 240 watts peak. The circuit was powered by four 2N3055 power transistors configured in push-pull pairs. A 2N3054 transistor was used as a driver to the four output transistors. The 2N3054 and it's bias adjustment pot were mounted to a heat sink near the audio isolation transformer (see photo below).
Unlike the Beatle and Westminster amps, which connected the output from the OTL power amp circuit directly to the speakers,