Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: frpax on November 27, 2018, 10:49:14 am
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Hi guys,
So on this 5F6A that I'm building, I'v got it all together, tubes in, speakers hooked up, ready to bias.
However, when I'm trying to read the plate voltage (pin 3 on the power tube sockets) I'm getting readings of around 370V and the plates inside one of the tubes glows pretty red (the other one doesn't).
I had the bias pot all the way one direction, figured that's too hot. So I turned the bias pot all the way the OTHER direction. Same voltage reading. 370-ish
I'm pretty sure I have the bias pot installed correctly and soldered in well....can I have a bad pot? Or is there something else afoot here?
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The bias pot does not change the 370v plate voltage. The bias pot controls the voltage on pin 5 of each output tube. Put the amp in standby mode. Connect your meter to pin 5 of a 6L6. Turn the bias pot from one end to the other. You should see the meter reading change. Now connect the meter to pin 5 of the other 6L6 and turn the bias pot from one end to the other. The meter reading should change exactly like the first 6L6. The voltage should change from about -40v to about -60v. What range do you actually have?
Leave the bias pot set to the highest meter reading for now and flip the STDBY switch to operate mode. Do either of the tubes glow red? If so, swap positions with the two 6L6s. Does the same tube glow red?
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The bias pot does not change the 370v plate voltage. The bias pot controls the voltage on pin 5 of each output tube. Put the amp in standby mode. Connect your meter to pin 5 of a 6L6. Turn the bias pot from one end to the other. You should see the meter reading change. Now connect the meter to pin 5 of the other 6L6 and turn the bias pot from one end to the other. The meter reading should change exactly like the first 6L6. The voltage should change from about -40v to about -60v. What range do you actually have?
Leave the bias pot set to the highest meter reading for now and flip the STDBY switch to operate mode. Do either of the tubes glow red? If so, swap positions with the two 6L6s. Does the same tube glow red?
I'll check it and get back to you. Thanks for the help!