Hello everyone,
I'm currently in the process of restoring my old Knight Kit 32W stereo integrated amplifier, model 83 YU 933. I found this amp with a cut power cord and no tubes, so I know it must have had some issues that someone either couldn't figure out or didn't feel it was worth it.
I started by replacing all the capacitors (except for two ceramic disks that I don't have on hand). I had purchased the 12AX7 tubes and a single 7025 from a member of a different forum a while back, which were supposedly all tested and good. I purchased a Mullard 5AR4 reissue and four Sovtek EL84M outputs, matched, to complete the tube compliment. The amp originally came with 7189 outputs. I did find a single 1W 33 ohm resistor that had burned and was in two pieces, which I of course replaced. This went to heater pin 4 on the 7025.
Upon initial test, the amp sounded good for about two minutes (apart from a small hissing sound), and then my issue occurred. The right channel began to pop, emit a high pitched whine, and then lose volume.
I checked resistance on the cc resistors under chassis and found that 70% of the ones I tested were out of tolerance, so I replaced all under chassis except for one odd ball size that I don't have, but will order. Found one bad solder joint on the right channel phase inverter.
The hiss is now gone, thanks to tossing the original cc resistors, however the problem still persists. I noticed that one of the right channel EL84M output tubes began to flash brightly this time I retested. I of course cut power immediately. Sounds almost perfect for two minutes or so.
I have not made any voltage measurements yet, I wanted to ask you guys for advice before I start chasing things around. If you have any suggestions on which direction I should head next, feel free to chime in!
Thank you,
Dan
I'm currently in the process of restoring my old Knight Kit 32W stereo integrated amplifier, model 83 YU 933. I found this amp with a cut power cord and no tubes, so I know it must have had some issues that someone either couldn't figure out or didn't feel it was worth it.
I started by replacing all the capacitors (except for two ceramic disks that I don't have on hand). I had purchased the 12AX7 tubes and a single 7025 from a member of a different forum a while back, which were supposedly all tested and good. I purchased a Mullard 5AR4 reissue and four Sovtek EL84M outputs, matched, to complete the tube compliment. The amp originally came with 7189 outputs. I did find a single 1W 33 ohm resistor that had burned and was in two pieces, which I of course replaced. This went to heater pin 4 on the 7025.
Upon initial test, the amp sounded good for about two minutes (apart from a small hissing sound), and then my issue occurred. The right channel began to pop, emit a high pitched whine, and then lose volume.
I checked resistance on the cc resistors under chassis and found that 70% of the ones I tested were out of tolerance, so I replaced all under chassis except for one odd ball size that I don't have, but will order. Found one bad solder joint on the right channel phase inverter.
The hiss is now gone, thanks to tossing the original cc resistors, however the problem still persists. I noticed that one of the right channel EL84M output tubes began to flash brightly this time I retested. I of course cut power immediately. Sounds almost perfect for two minutes or so.
I have not made any voltage measurements yet, I wanted to ask you guys for advice before I start chasing things around. If you have any suggestions on which direction I should head next, feel free to chime in!
Thank you,
Dan