Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: leevc5 on March 16, 2018, 04:18:50 pm
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B+ off of 5Y3 without other tubes installed is 470 - that seems OK
but
B+ with tubes installed drops to 240? Should be ~360
6V6 pin 8 cathode 48V??? Should be ~20
What might cause this weird voltage stuff?
Have swapped out all the tubes and readings are consistently puzzling.
Also, when power switched on after a couple of seconds there is a pop or click noise. Doesn't continue or repeat, just one time every time powering up.
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6V6 G1 voltage??
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What is the voltage on pin 5 of each 6V6? Should be zero.
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What is the voltage on pin 5 of each 6V6? Should be zero.
When measuring pin 5 on each 6V6 starts at ~1.6 and drops tp .5V and stays there.
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Disconnect both coupling caps between the PI plates and 6V6 grids and recheck the voltage on pin 5 of each 6V6.
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6V6 G1 voltage??
where/how do I measure G1 and what is it?
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G1 = pin 5
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Disconnect both coupling caps between the PI plates and 6V6 grids and recheck the voltage on pin 5 of each 6V6.
With coupling caps disconnected from PI still reads .5V but does not start higher and drop down just immediately .5.
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With those two caps still disconnected do the B+ voltage readings go up? And does the pin 8 voltage go down to a more reasonable value?
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With those two caps still disconnected do the B+ voltage readings go up? And does the pin 8 voltage go down to a more reasonable value?
B+ still low ~254 but pin 8 now at 24 which is more in line.
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Reconnect only one of those caps and then recheck pin 8 voltage. If voltage goes up, replace that leaky cap and recheck pin 8 voltage. If still approx. 20 volts, install the other cap. If voltage goes up, replace that leaky cap and recheck pin 8 voltage. If still approx. 20 volts, throw away the leaky cap(s).
With power off, measure resistance between chassis and pin 5 of each 6V6. What have you?
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Old build, new build?
i.e. did it work right once or are you first-time smoke-testing?
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Reconnect only one of those caps and then recheck pin 8 voltage. If voltage goes up, replace that leaky cap and recheck pin 8 voltage. If still approx. 20 volts, install the other cap. If voltage goes up, replace that leaky cap and recheck pin 8 voltage. If still approx. 20 volts, throw away the leaky cap(s).
With power off, measure resistance between chassis and pin 5 of each 6V6. What have you?
Thank you for your patience and persistence.
Unfortunately, just took a step backwards. Tried the leaky cap replcement process without success and now with both caps disconnected am back up to 48V @ pin 8?????
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Old build, new build?
i.e. did it work right once or are you first-time smoke-testing?
New build, first time to fire it up.
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OK, so it ain't the caps. What about the resistance check?
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OK, so it ain't the caps. What about the resistance check?
Infinity - Open Loop
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Infinity - Open Loop
You are most likely missing a ground connection to the junction of those two 220K grid resistors. Fix it and things will get a lot better.
If this is a Hoffman board the most likely problem is a missing under board jumper from the junction of those two 220K resistors to the negative terminal of a 16µF filter cap. If using another layout just look.
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Infinity - Open Loop
You are most likely missing a ground connection to the junction of those two 220K grid resistors. Fix it and things will get a lot better.
If this is a Hoffman board the most likely problem is a missing under board jumper from the junction of those two 220K resistors to the negative terminal of a 16µF filter cap. If using another layout just look.
That Dr. Sluckey sir was the problem!
You got me thru many a 5F1 weirdities and have got me thru my first 5E3 build to success. If there was a Nobel prize for Tweed Amp Troubling Shooting you should certainly win the award.
Thank you one again.
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If there was a Nobel prize for Tweed Amp Troubling Shooting you should certainly win the award.
+1 Sluckey definitely holds the record for correctly trouble shooting my amp builds!
with respect, Tubenit
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If there was a Nobel prize for Tweed Amp Troubling Shooting you should certainly win the award.
+1 Sluckey definitely holds the record for correctly trouble shooting my amp builds!
with respect, Tubenit
He also holds the record correctly shooting amp builder problems.
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He also holds the record correctly shooting amp builder problems.
I try to treat all equally. Give'm what they ask for. :icon_biggrin:
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I try to treat all equally. Give'm what they ask for. :icon_biggrin:
:laugh: