UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

cathoderay57 · 25th May 2019, 4:05 pm

Hello again, well, guess what, the fault has returned. The fault seems to recur after the set has been switched off for >24 hours. I was still unhappy with the T3 (OC71) voltages so I desoldered it. On the Avo the Collector-emitter leakage resistance measured only 8.5k which didn't look good to me. I replaced it with a spare that had a measured leakage resistance of 500k. I also found a couple of discrepancies from the RP38A service sheet. On my radio, R10 is 82R (not 150R) and R11 is 180R (not 150R) but I left these as-is. I repeated the set up of the quiescent o/p current. With RV4 set to s/c I could only get the current down to 3.7mA (not the specified 3mA) and the sound became distorted. So I readjusted RV4 up to a clear sound threshold which gave a measured current of 4.7mA. The o/p transistors are still running cold to the touch so we'll see how it goes. Cheers for now, Jerry.

25th May 2019, 4:05 pm	#20
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,386	Re: Hacker Hunter Hello again, well, guess what, the fault has returned. The fault seems to recur after the set has been switched off for >24 hours. I was still unhappy with the T3 (OC71) voltages so I desoldered it. On the Avo the Collector-emitter leakage resistance measured only 8.5k which didn't look good to me. I replaced it with a spare that had a measured leakage resistance of 500k. I also found a couple of discrepancies from the RP38A service sheet. On my radio, R10 is 82R (not 150R) and R11 is 180R (not 150R) but I left these as-is. I repeated the set up of the quiescent o/p current. With RV4 set to s/c I could only get the current down to 3.7mA (not the specified 3mA) and the sound became distorted. So I readjusted RV4 up to a clear sound threshold which gave a measured current of 4.7mA. The o/p transistors are still running cold to the touch so we'll see how it goes. Cheers for now, Jerry.