| Author | Message | ||
| Mike H |
My amp is a 112RP65, GP-1. I just replaced all electro caps, the driver transistors, and ops amps. I have new JJ E34L tubes bias at 25mA. The amp sounds good, except I get a slight distortion. I've swapped tubes out (3 different pairs), swapped cords, speakers, swapped op amps, resoldered one bad looking transformer lead to the PC, and still the problems exists. The only thing I found that I suspect is that both 3.9 ohm, 1 watt. cathode resistors are measuring 5.1 ohms. I measured them out of the board to ensure. So, would these resistors, being nearly 25% out of spec likely cuase this? Also, I still get very slight bias drift. Anyone think these things are related? I was going to replace these resistors when I had the board out, but no one locally had carbon comp resistors. Anyone used metal film for these? | ||
| Mike H |
I used 2N6488 driver transistors. Could I be hearing slight oscilation from these transistors? | ||
| Steve Kennedy (admin) |
Take the 100mV and 3V insert jack outputs and run them to a headphone or another power amp. If these still sound distported then you have a preamp problem that will need to be found, not an output stage problem. If the preamp output is clean, then there would be no harm in replacing any discolored components (such as resistors) in case they are influencing the sound. Steve | ||
| Mike H. |
I ended up replacing the 3.9 ohm resistors, resistor & caps on the tube sockets and resoldering a few questionable looking things and the problem is fixed. Not sure which thing fixed it, but probably needing fixing anyway. Terry suggested doing these things and my amp now sounds great! Better than it's sounded in years. |
Tue, 03/25/2014 - 09:26
#1