Bassman AB165 wrong voltages
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Bassman AB165 wrong voltages
Hi anyone can help? wrong voltages in red
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Re: Bassman AB165 wrong voltages
I don't see anything alarming.
Re: Bassman AB165 wrong voltages
the voltage after the rectifier diodes is 329v, I only highlighted the voltages that seemed too different from those in the schematic
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Re: Bassman AB165 wrong voltages
Check the value of the 22k PI tail resistor by measuring from where you have marked 149V to ground. It may have drifted up.
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Re: Bassman AB165 wrong voltages
With the amp in play mode what do you have for voltage at the input to the choke, and as noted on the schematic what do you have for negative bias voltage ?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Bassman AB165 wrong voltages
you're absolutely right, I took it off the circuit and it measured 54k, it was the only one in that area that I hadn't replaced. I have now put 10k + 15k in series and the voltages are much bettermartin manning wrote: ↑Wed Mar 02, 2022 11:34 am Check the value of the 22k PI tail resistor by measuring from where you have marked 149V to ground. It may have drifted up.
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Re: Bassman AB165 wrong voltages
Great!nabokov wrote: ↑Wed Mar 02, 2022 1:06 pm...I took it off the circuit and it measured 54k, it was the only one in that area that I hadn't replaced. I have now put 10k + 15k in series and the voltages are much better.martin manning wrote: ↑Wed Mar 02, 2022 11:34 am Check the value of the 22k PI tail resistor by measuring from where you have marked 149V to ground. It may have drifted up.
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Re: Bassman AB165 wrong voltages
I am assuming that your reported -57 is what you had before you replaced that 10K resistor in the bias circuit, if not then the bias voltage is still too high!
What was going on before you replaced that resistor was that the output tubes where not idling and pulling current, in that state the power supply voltage was not getting pulled down and such was the reason for your high voltage readings through out the amp.
What was going on before you replaced that resistor was that the output tubes where not idling and pulling current, in that state the power supply voltage was not getting pulled down and such was the reason for your high voltage readings through out the amp.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Bassman AB165 wrong voltages
Yes it's true, it was before I replaced the 22k resistor. In addition, the 2 10K resistors and the 15K on the bias potentiometer were also gone.Stevem wrote: ↑Thu Mar 03, 2022 11:25 am I am assuming that your reported -57 is what you had before you replaced that 10K resistor in the bias circuit, if not then the bias voltage is still too high!
What was going on before you replaced that resistor was that the output tubes where not idling and pulling current, in that state the power supply voltage was not getting pulled down and such was the reason for your high voltage readings through out the amp.
All this research began to solve a hum promblem.
Now it's almost gone. The voltages are ok but I still have 329v AC (instead of 320v AC) coming out from the secondary of the PT. Anyone know a way to fix?
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