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Old 9th November 2006, 12:27 AM   #1
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Location: Hong Kong
Default What is the correct plate voltage in this circuit?

I am using the following circuit to take up current source from TDA1541 with tube output. The original circuit is using 6DJ8 and R105 is 10K 2W. By adjusting B+ to 160V, the plate voltage of 6DJ8 is 90V (Simens 6DJ8) and 100V (Mullard 6DJ8). It sounds good.

In some forum, it says changing the tube to 396A will produce even better result therefore I made a try and converted the PCB to accomodate 396A. I have also changed R105 to 12K 2W as recommended in the forum.

After adjusting B+ to 160V, The plate voltage of 396A is 119V (Western Electric 396A). The sound is more detail and density but the right channel has hum. I only converted the PCB on the left channel and did nothing on the right channel. Questions --

1. What should be the correct plate voltage for 396A in this circuit?
2. Should I adjust the B+ or adjust the R105 to obtain the correct plate voltage?
3. Since I did nothing on the right channel, what may cause the hum? Could a bad tube cause it?

Thanks regards
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Old 10th November 2006, 01:24 AM   #2
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Anyone can help me out?
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Old 10th November 2006, 01:43 AM   #3
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Location: Adelaide South Oz
Default A quick answer

Haven't done an analysis
if the design is decent then it should be at 2/3rds of the rail voltage so I would expect it to be 100 to 105 Volts.
If its not I would change the cathode bias resistor until it is.
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