| Author | Message | ||
| David Pokotylo (davidp) Username: davidp Registered: 01-2009 |
So, after replacing ALL electrolytics, the cap can resistors, the 3.9ohm emitter resistors, as well as the larger resistors (3.3K, 1K) near the board mounted caps on my RD65-112 with 2w metal films, and a variety of tubes, I'm still getting appreciable bias creep (e.g. 6 ma over 1 1/2 hrs from cold)... Any idea where to troubleshoot this?? | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Which amp are we talking about? If it's the SS driver, I 'd look at the driver transistors first. | ||
| David Pokotylo (davidp) Username: davidp Registered: 01-2009 |
This is an early 80s RD112-65, no tube driver, with 6l6s. Schematic lists three different transistors -- I assume JE1692 are the driver transistors, and is there a current replacement? | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
According to Lars(who is a HELLUVA lot more informed than I am!) the crossover is here: The GP/GD-2 board takes the 2N6292 as a replacement for the JE1692, and this one is available from Mouser (and no doubt elsewhere). Good luck and let us know. Mike. | ||
| Mike Griffin (mgriffin155) Username: mgriffin155 Registered: 02-2014 |
I replaced the cathode driver transistors in my RD65-112 with 2N6888G (NPN 15A 80V 75W). I also replaced the 3.9 ohm emitter resistors. Previous to that I had replaced the tubes. Before replacing the transistors, the bias was at 25mV across one 3.9 ohm resistor and 50mV across the other. The factory 3.9 resistors were way off at 4.5 and 4.8 ohms. After replacing the 3.9s and transistors, the two tubes balance out very well and the readings across the 2 3.9s are within .5mV of each other (25mV and 25.5mV). I think I was lucky and got a well matched pair of resistors and transistors from Mouser. BTW: the amp does take awhile to warm up for the readings to stabilize. Mine takes about 45 minutes to an hour. -Mike |
Tue, 03/25/2014 - 09:34
#1