I have completed my build of the Elekit TU-8200 and am having an issue with the left channel. No sound and the left channel tubes are significantly cooler than the right. I did modify the build slightly by replacing the standard volume POT with a TKD 2CP-601 POT and by replacing the 8200 transformers with LL2777B transformers (the 8200VK option).
The schematic for the 8200 is here:
Initially, the left channel would work fine for 5 to 10 minutes and then drop out. I did some basic research and troubleshooting (swapping tubes around, checking cables and connections…) and made an assumption that the Q1 transistor, part of the active automatic bias circuit, was bad and replaced it with another A1266 transistor. Since this replacement I have had no sound on the left channel after powering the amp. I have done some basic troubleshooting since then, visual, continuity, hot spots and I am not seeing anything obvious to my limited experience. I’m at a loss and am concerned that my limited troubleshooting ability has made things worse.
Below are my readings at the test points listed in the schematic:
Any guidance and advice is greatly welcomed.
FYI I have cross posted this in r/AskElectronics.
Bill
The schematic for the 8200 is here:
Initially, the left channel would work fine for 5 to 10 minutes and then drop out. I did some basic research and troubleshooting (swapping tubes around, checking cables and connections…) and made an assumption that the Q1 transistor, part of the active automatic bias circuit, was bad and replaced it with another A1266 transistor. Since this replacement I have had no sound on the left channel after powering the amp. I have done some basic troubleshooting since then, visual, continuity, hot spots and I am not seeing anything obvious to my limited experience. I’m at a loss and am concerned that my limited troubleshooting ability has made things worse.
Below are my readings at the test points listed in the schematic:
| Test point | Measurement | Test Point | Measurement | Expected measurement |
| 1 | .37 VDC | 2 | 3.8 VDC | 3.2 - 3.7 V |
| 3 | .26 VDC | 4 | 3.7 VDC | 3.2 - 3.7 V |
| 5 | 12 VDC | 6 | 118 VDC | 100 - 120 V |
| 7 | 15 VDC | 8 | 117 VDC | 100 - 120 V |
| 9 | 22 VDC | 10 | 119 VDC | 195 - 220 V |
| 11 | 1.1 VDC | 12 | 1.1 VDC | 1.0 - 1.2 V |
| 13 | -9.1 VDC | 14 | -19 VDC | -12 - -24 V |
| 15 | 75 VDC | 16 | 300 VDC | 265 - 290 V |
| 17 | 0 VDC | 18 | .44 VDC | 0.4 - 0.55 V |
| 19 | 34.0 VDC | 20 | 283 VDC | 255 - 280 V |
| 21 | 33.8 VDC | 22 | 276 VDC | 250 - 275 V |
| 23 | 33.8 VDC | 24 | 289 VDC | 255 - 280 V |
| 25 | 304 VDC | 270 - 300 V | ||
| 26 | -32 VDC | -29 - -35 V | ||
| 27 | -34 VDC | -30 - -36 V | ||
| 28 | 6.3 VDC | 5.6 - 6.4 V | ||
| 29 | 6.6 VDC | 6.0 - 6.8 V |
Any guidance and advice is greatly welcomed.
FYI I have cross posted this in r/AskElectronics.
Bill
