38-116 died the 3rd time! Guidance Please?
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1. When you say G2 voltages are different, you mean 6L6s? If yes, aren't they connected together? Why are they then different? Or do I miss something?
2. Can you swap the two 6A8 places and confirm that nothing has changed?
3. Is the rectifier output (after the choke) what it is supposed to be or is it also lower?
(This post was last modified: 03-29-2013, 10:37 PM by morzh.)
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Sounds like you may have a leaky 6L6 drawing excessive current, or a power supply issue. Check especially the B- supply (bias supply) 123A and the accompanying resistor network (109, 110, 111, 112, 114, 115, 116, etc.) this is also the grid bias for the 6J5. If the bias is wrong, the plate current on that tube will change. Also check speaker field coil, which is part of this network.
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I would also first pop both 6L6 tubes and see if the voltage goes back to normal.
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Thanks gang, after my last blunder I figured you two would never come back!
I did try a pair of 6L6s out of my Scott and no joy. I will first remove the existing ones and see what happens to the B+. After that, on to the negative side as Brenda suggested. Seems something is loading it down as mentioned previously, about 3 seconds after power up the voltage seen at say the plate of a 6L6 will go up approaching 400V then the load slowly starts as the other tubes warm up and what you see are low voltages. Good spot on the 6J6 Brenda.
Mortz as for your questions, remember ladies first.
1. Yes they are, let me correct my previous posting Mortz. Too many numbers running around. Thanks
2. On the 6A8s the voltages were updated in my previous post. Apparently my tube extender was not in well. They are now more in line with just low!
3. The measurement of the B+ line right after the choke is accurately reflected in the G2 measurements on the 6L6. Low with respect to ground.
Off to the garage in the morning.
Regards, Jerry
A friend in need is a pest! Bill Slee ca 1970.
(This post was last modified: 03-30-2013, 01:11 AM by jerryhawthorne.)
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Jerry
1. So, to interpret your answer #3, your B+ is low. Right?
2. Have you checked ALL your electrolytics? And I mean - ALL. There are a few, all need to be checked.
3. have you checked both choke AND field coil resistances for being too high?
4. Also when I asked about measuring B+, I suggested doing it without 6L6s in place.
(This post was last modified: 03-30-2013, 12:08 PM by morzh.)
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Mortz, going down to work on it. I will give a rough answer to your questions.
1. Correct, about 40V low to ground.
2. All have been replaced Mortz perhaps a new one went South. Part of today's efforts.
3. Will check today Mortz.
4. I understand and will do that with them removed and see what happens.
Thanks for hanging in there.
Jerry
A friend in need is a pest! Bill Slee ca 1970.
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Pay special attention to those caps that load the B+ immediately or via a low resistance.
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Well, after running through chokes/transformers, resistors etc. I never realized how many parts in there tested just fine! Depressing. Going through the caps in the area suggested by Brenda was a real PIA. They had previously been replaced with the total removal of the old cans. I hate that. So we went through, removing the old and installing the new. Probing around I saw a little spark down underneath everything. A little more probing and moving of wires and the radio now is working just fine! Apparently a couple wires were intermittently shorting out.
In this searching it also looks as though I missed adding one cap on the restuff. This was cap 123A. I jumpered one in there and it made no difference. Should I put one back in there?
Radio has played nicely for 4 hours and the transformer is not even warm.
On the low voltage the transformer was warm to the touch after 5 minutes. Also the 6L6s you couldn't pull out by hand after a couple of minutes, now no problem.
At 115V AC I'm getting 300V on the screens of the 6L6s, just like I should.
Thanks all of you for your patience. After this I may give up on radios. Regards to the two that stuck with me on the last two deaths. Couldn't have done it without your help. Now if my friend will just pick it up before it undergoes the next death.
Jerry
A friend in need is a pest! Bill Slee ca 1970.
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Well, it's good it plays.
The 123A cap is still needed though. It can be a low-voltage electrolytic.
And, don't forget - the Positive goes to the Chassis in this one.
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Good point Mortz, why waste a 450V.
Jerry
A friend in need is a pest! Bill Slee ca 1970.
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