love pa amps
New Member
I had to completely disassemble and rebuild this amp for several reasons, 1) the wafer type tube sockets were installed from the top instead of the bottom, which looked awful and also placed the solder terminals on the sockets too close to the edge of the socket hole on the chassis where they had started to carbon track and short to ground 2) the front and sides of the chassis were in good shape but the top of the chassis and the transformers were badly discolored by rust, corrosion, peeling paint, etc, 3) the mounting socket for the filter cap was broken in several places, 4) the caps and resistors were all out of spec and the wiring was a sticky, moldy mess. After full disassembly I sanded, primed the top of the chassis and repainted it with RUSTOLEUM "metallic" gold which was a 95% match to the original Heathkit color. I used blue painters tape to mask the front, back and sides of the chassis which joined the new and old paint in a way that it appears to be a perfect match. After I removed their screws, the transformers were sanded, primed and repainted with gloss black Rustoleum. I installed 4 NOS brown mica top mount style tube sockets. Sprague 715P 600v .047 mfd coupling caps and 1%, 1/2 watt film resistors. I wired the amp with 20 gauge color-coded wire, RED-B+ /BLACK-B- / BLUE-audio / GREEN-filament, and WHITE for ac line. The filter cap was a MAGNAVOX multisection twist mount which reformed quickly and tested good on my Sprague tel-ohmike TO-5, it has been running cold for a week now with no problems. The only changes I made were:
upping the output cathode resistor to 200 ohms (recommended by Heathkit) and changing the main B+ resistor from 100 ohms 2 watt carbon to 600 ohms 5 watt wirewound to decrease the B+ voltage to match the voltages on the diagram.(same problem/cure I made on 2 other UA-1 amps I rebuilt) I re-assembled the amp using the original Heathkit assembly manual, following all steps as printed. The amp has been running for a week now with no problems and sounds great!!
upping the output cathode resistor to 200 ohms (recommended by Heathkit) and changing the main B+ resistor from 100 ohms 2 watt carbon to 600 ohms 5 watt wirewound to decrease the B+ voltage to match the voltages on the diagram.(same problem/cure I made on 2 other UA-1 amps I rebuilt) I re-assembled the amp using the original Heathkit assembly manual, following all steps as printed. The amp has been running for a week now with no problems and sounds great!!
