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Can I just put a DMM @500 voltsDC positive probe on pin#3 of my Power tubes and Negitive to ground to see plate voltage of my amp?I know they sell Bias probes that have a switch to see Plate and current....I just wanted to know if I could do it this way...Thanks DAB
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That will work, as long as your amp runs at less than 500V. What amp are we talking about here? If it's a small 6V6 or EL84 amp, you're probably okay. Bigger amps might be pushing it with only 500V capability. Tell us the amp in question!
Justin
PS: KEEP IT SAFE! "Dumbass" or not, we want you around for a while.
"Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
"Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
"All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister - -
If you are nervous at all about probing hundreds of volts (prob should be if you haven't done it before) it is good to use probe clips too, so you don't have to reach inside a working amp. Clips the leads to pin 3 and to ground then turn the amp on.Comment
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An additional caution is to probe (or clip) carefully and take care not to short out to adjacent pins. One inadvertent slip that shorts pin 3 (the plate) to pin 2 (the heater) will cause various damage to the tube / circuitry / power transformer. On your Fender amp it is convenient to just measure the B+ where the red output transformer wire is connected to the parts board. The voltage there is nearly the same as that at pin 3 of the power tube. You would sill connect the negative meter lead to chassis ground.Comment
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My 63 Fender Bandmaster I just got some Tung Sol 6l6gc there ok sounding but seem soft..I was using Mesa str but the pins are so big and I had to retention all the sockets..I am getting a bias tool I have not had it done in a while....Save a trip to skip simmons shopComment
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thanks tom..Thats what I wanted to know....Comment
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That is how you measure the voltage at any point in the circuit, ground the black probe, and probe with your red probe. Unless you want to know the voltage between two points other than ground. But when we say the plate has 400v on it, we mean to ground. When we say the tube has 400v across it, we mean plate to cathode. Of course in most of our amps the cathodes are grounded, so the difference is academic there. And of course your meter must be capable of measuring voltages as high as the circuit under test uses.Education is what you're left with after you have forgotten what you have learned.Comment
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For safety purposes, also note that your probes & their cables have their own voltage rating. A 1000V meter doesn't do much for you if you have 500V probes!Originally posted by Enzo
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A tube extender might be worth buying if you will be doing much amp work, makes reading the pin voltages safer (for you and the amp) and also easier.
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