Hi - I'm a newbie here. I've been a guitar amp hobbyist for 20+ years and have accumulated a large number of pulls from garage sale electronics. Some of the old tubes I've acquired have some value but I don't have a tube tester. Some I can plug into a guitar amp to see if they function, but that is all. Is there a way to test strength of a tube in circuit with a VOM?

You could use a VOM to test the filament / heater as well as to test for shorts between the various elements. The tube guide available on this site would be helpful in this regard by indicating the pin out of a specific tube. As far as reliable emission or transconductance testing - I don't think you'll be able to without very complex and expensive modifications. In the long run, it would probably be much more cost effective (and exponentially simplier) to buy a mid-level tube tester.

Thanks. I guess I'll look for a used tube tester.

:You could use a VOM to test the filament / heater as well as to test for shorts between the various elements. The tube guide available on this site would be helpful in this regard by indicating the pin out of a specific tube. As far as reliable emission or transconductance testing - I don't think you'll be able to without very complex and expensive modifications. In the long run, it would probably be much more cost effective (and exponentially simplier) to buy a mid-level tube tester.
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Hi

Testing by substitution, like you are doing, is the best way to check tubes. Even a tube tester can't tell if a tube will work in the circuit.

You could check emission by measuring cathode voltage. Most circuits have a cathode resistor to B-. Tubes with higher emission will have more voltage drop across this resistor.

A properly operating circuit with 6L6 output tube may have 15 volts across the cathode resistor. A weak tube may only give a 10 volt reading but still operate. Lower voltage would indicate low emission.

Norm

:Hi - I'm a newbie here. I've been a guitar amp hobbyist for 20+ years and have accumulated a large number of pulls from garage sale electronics. Some of the old tubes I've acquired have some value but I don't have a tube tester. Some I can plug into a guitar amp to see if they function, but that is all. Is there a way to test strength of a tube in circuit with a VOM?
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Norm is, of course, correct - though in a very limited scope. Using your amplifier to evaluate tube performance is strictly limited only to the tubes (or equivalents) that the amplifier uses. How are you going to test that loctal in an octal socket, etc.? Testing in equipment will subjectively verify that the tube functions - but will give no reliable objective data for comparison. A tube with borderline function may sound as good to your ears as a NIB tube with peak performance. You mention value - so I suppose you are considering selling them. A buyer will be much more impressed if you state that the tube measures 28 out of 30 on brand X tube tester - rather than "it works in my amp".......

:Norm is, of course, correct - though in a very limited scope. Using your amplifier to evaluate tube performance is strictly limited only to the tubes (or equivalents) that the amplifier uses. How are you going to test that loctal in an octal socket, etc.? Testing in equipment will subjectively verify that the tube functions - but will give no reliable objective data for comparison. A tube with borderline function may sound as good to your ears as a NIB tube with peak performance. You mention value - so I suppose you are considering selling them. A buyer will be much more impressed if you state that the tube measures 28 out of 30 on brand X tube tester - rather than "it works in my amp".......
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i have a tube tester i live in adamsville alabama
i would be glad to test the tubes if you send them to me.my phone # 2056745134.no charge i just love tinkering with old things.i am a retired electronic tec.call if you would like