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RH84 test amp: multiple problems found ...
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Posted on September 23, 2016 at 17:24:17 | ||
Started working on the RH test amp again this afternoon and found a number of problems. A) Several suspect looking solder joints on driver tube socket, re-flowed all pins with Kester 44 60/40 rosin core solder. I also reflowed the RCA input jack connections. B) Right channel red plating of EL84. Found the LM317 cathode CCS and bypass cap to be damaged. Remove the damaged parts are reconfigured both channels to run off one LM317 cathode CCS. C) The 5.1V X 3 zener diode string connected to right channel EL84 G2 was shorted out. Removed the damaged parts and reconfigured both channels to run off one diode string for both channel G2's. D) reports of excess noise showing up on my distortion analyzer was due to a ground loop. When I added a ground defeat plug to the AC line cord, the THD+N measurements returned to normal. I might need to add a bit more filtering to get the AC ripple at speaker posted below 5mV, but it is OK for listening on some bookshelf speakers. The sound from my bookshelf speakers is much improved now that these corrections have been made. Edit: @ 1.2W power output RT Channel THD = .77% THD+N = .79%
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circuit in question, posted on September 26, 2016 at 18:03:18 | |
Posts: 17260
Location: So. Cal. Joined: February 9, 2002 |
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