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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Dyna Stereo 70 biasing problem posted by Darth_Thorium on November 10, 2002 at 11:46:06:
First - exchange the tubes from channel to channel to see fi the problem follows the tubes (this is probably not the problem but no harm in getting the tubes as the problem out of the way)Next - pull all four output tubes. Now check the voltages on the pins of the "good" channel and compare them aganist the voltages on the pins of the output tubes of the problem channel.
You should find one of two things on the problem channel a) the bias voltage on pin 5 is very negative (like negative 45 volts) on the problem chanel or b) the voltages on pins 3 & 4 are low or missing.
I think the problem will be (a) so lets focus there. Check the voltages on the _ends_ of the two bias adjust pots - both pots should be the same (about - 40VDC on one ends and - 28VDC on the other ends). If you get this now measure the voltage on the center pin of each bias pot _as you rotate the bias pot for that chanel_. The voltage should range close to the same voltages you measured on the pot ends. I suspect that you may find that the problem channel's voltage does not vary from the most negative voltage.
If you pass this test run it again but this time measure the voltage at pin 5 of the output tubes. You should get similiar results if the circuit is OK.
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Follow Ups
- Try This Re: Dyna Stereo 70 biasing problem - Joe Curcio 12:20:24 11/10/02 (1)
- What Joe said - John EH 13:47:03 11/10/02 (0)
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