Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jammied on October 02, 2020, 07:57:06 pm
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Ok this might be a dumb question?!
I was playing around today with a amp. And had the guitar plugged in .
Started checking voltages and pin 3 on the 6l6' were have wild voltages swings. Burned one of my meters up testing . Went way over 900v.
Never tested with a guitar plugged in ..... is this normal? Or did something in the amp go bad?
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... Started checking voltages and pin 3 on the 6l6' were have wild voltages swings. Burned one of my meters up testing . Went way over 900v.
Never tested with a guitar plugged in .....
Was there any sound from the amp at the same time you tried that measurement? If not, I don't follow how the plate voltage was swinging wildly (unless there were no filter caps in the power supply).
... I was playing around today with a amp. And had the guitar plugged in .
... wild voltages swings. Burned one of my meters up testing . Went way over 900v.
Never tested with a guitar plugged in ....
The 2 items above say opposite things. Guitar or no?
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I took the second statement to mean "Never tested with a guitar plugged in before today"
With a guitar plugged in and someone wailing away on it there will be wildly swinging voltages on the plate. Enough to take out a cheap meter. Heck, I would not even expose my Fluke 87V to that scenario.
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I took the second statement to mean "Never tested with a guitar plugged in before today"
With a guitar plugged in and someone wailing away on it there will be wildly swinging voltages on the plate. ...
Agreed if that was the intention fo that second statement.
Don't measure output tube plate voltage while playing Jammied!! Or get yourself a 1000:1 high-voltage probe (https://www.digikey.com/product-detail/en/b&k-precision/PR%252028A/PR28A-ND/262491?utm_adgroup=Test%20Leads%20-%20Banana%2C%20Meter%20Interface&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Product_Test%20and%20Measurement_NEW&utm_term=&utm_content=Test%20Leads%20-%20Banana%2C%20Meter%20Interface&gclid=Cj0KCQjwwuD7BRDBARIsAK_5YhUJ7UTtpyLOSr2k8-kkp0fb9MQMev6z-4Efqphr2h0rmT72ux6nzDkaAvItEALw_wcB)!
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My view is that a power tube plate is a node best avoided by any test equipment. As there’s too high a likelihood of the measurement equipment causing instability / being damaged.
I prefer to monitor the HT voltage instead; at idle, any difference between the HT node that supplies the plate, and the actual plate voltage, will be negligible.
I came to this position 35 years ago, after my new Fluke got frazzled when I left it clipped on to just a 12AT7 reverb driver plate :sad2:
I realised that it should have been expected, as a transformer coupled plate swings to twice the HT voltage at full power, and due to back emf, even higher than that when overdriven.
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Yep. Guitar plugged into the input of the amp.
After posting the question common sense kicked in . That is the amplified signal.
Usually don't have anything plugged into the input of the amp while checking voltages and all controls at zero.