Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: KimboDb on August 23, 2017, 07:37:48 pm
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could someone help with the testing for high voltage on the preamp tubes. I have a multimeter and I just want to make sure I don't do it wrong. Is this test to make sure I have the tis a 6.3 volts to the preamp tubes or am I checking for too much power to the preamp tubes
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I'm not sure what you're asking :dontknow:
6.3VAC is filament, typically pins 4/5 n 9
what type meter do you have and how confident are you with it?
If you're new to this, measure up a couple batteries and make sure you get what you expect, if so, measure up some wall outlets and make sure you get what you expect.
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I have a radioshack true rms digital multimeter. the first step after buildup is test the preamp tubes sockets for high voltage, on the installation page is say
"Powering up the amp and setting the bias
After all connections have been made and double checked
Power up the amp with no tubes in the sockets. Using a multi-meter set on DC volts
Check to see if pins 1 and 6 on the pre-amp tubes have high voltage
9 pin tubes have different configurations.
Look at the schematic to see which pins should be measured.
Check pins 3 and 4 on 8 pin power tubes to see if they have high voltage.
Check Pins 7 and 9 on EL84 power tubes to see if they have high voltage.
Go to the Cathode biased section or the fixed bias section below
Depending on the amp you are building"
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sounds like you have the steps, do you have a good idea what the voltage "should be" without tubes? You probably won't get readings at the cathodes without tubes, with tubes that's the best info you can get :laugh:
what kind of bias are you using, fixed, or self?
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Pre-set meter to _DC_Volts. If possible, pre-set it to 500V range. (Auto-ranging meters will start on 0.2V range and have to re-range 4 times before they get a number.)
Black lead to a good ground. Use a clip-lead!
Red lead to one tube's Plate. I would really use a clip-lead so my hands were nowhere near that basket of venomous vipers!
Expect all no-tube Plate readings to be similar and about 400V. (They will be different when the tubes are in and warm.)
Different check: set meter to _AC_Volts_. Use clip leads to attach one probe to one heater pin, the other to the other. (This is more correct than measuring each to ground.) The no-tubes reading on a "6.3V" heater supply may run as high as 7V, no worries. It will drop when all the tube heaters are in and sucking.