Digital Tube Tester VS Analog Tube Tester

[danny davis]

The Digital tube tester , test the tubes at high voltage at 300 volts to 400 volts VS Analog Tube testers, test the preamp or power amp tubes at lower voltages?

Testing Tubes on an analog tube tester will PASS the test because the analog tube tester is testing them at a low voltage. But you slap those tubes that have passed the test and they will fail in the preamp or power amp because now they are in a 400 volt circuit.

Why do they fail with high voltage but now with low voltage?

Analog Tube testing , doesn't test the preamp or power amp tubes for Noise or Hum? but does a digital tube tester test the tubes for hum and noise?

The Digital tube tester , test the Plate current and Transconductance of a power tube, which analog tube tester don't?

Does an Analog tube tester, test the Transconductance of a preamp or power tube? I don't remember see a function on my analog tube tester

Power Tube Digital Tester:
**broken link removed**

Pre-Amp Tube Digital Tester:
**broken link removed**

Listen to your tubes with dual-RCA Direct Audio Output? is this to test for the NOISE of the preamp tubes?

 

[chuckey]

Preamplifier valves do not operate with 400V on their anodes, they might be operating from 400V, but have a 100K series resistor so the anode volts is only 250 at the most.
As far as I can see the only use for a valve tester is for matching valves in push pull configuration. As a valve ages and its emission falls, it takes less current - measuring the volt drop across the cathode resistor will tell you that. Balancing gm is only applicable for push pull circuits.
I have built valve equipment since 1960 and have been employed professionally working on valve equipment since about 1964, only stopping in 1990. I have fiddled with valve testers during various jobs, and while interesting, have not ever located a fault with one. I think these instrument are designed as accessories for "high end" $20,000 valve hi-fi sets.
Frank

 

[danny davis]

Balancing gm is only applicable for push pull circuits

Why do you need to balance the GM? what does the GM do?

I don't remember my Analog Tube Testing , testing the GM Transconductance of my tubes? was it called something else?

The Digital Tube tester, tests the Plate current

I also don't remember my Analog Tube Tester testing the plate current

My Analog Tube tester had a button to do a LIFE TEST which would load the tube and see if it was weak or not

I don't see this Digital tube tester doing that right?

Here is a picture

 

[chuckey]

Gm is short for mutual conductance (1/R), or if the grid volts changes by 1V how many mA the anode current changes by. With push pull output stages, while the anode currents could be equal between the valves, they could change by a different amount for the same voltage changes on their grids. Because of the equalising effect of the output transformer, the added distortion is very low (>.1%?). The standard British valve tester was made by Avo. it had a test buton which tested the gM. The only way to test the "life" of a valve is to see how much residual life there is left in the cathode, to do this you have to reduce the filament voltage by a relatively small amount, say .1V. if the filament is capable of oversupplying electrons at 6.3V, reducing the fils to 6.2, should still supply enough electrons for the normal operation of the valve. A test button would work but it must be held in for say, 30 seconds to allow the filaments to cool to their new operating temperature, so the emission of the cathode also falls to its new level.
Frank

 

[danny davis]

The only way to test the "life" of a valve is to see how much residual life there is left in the cathode, to do this you have to reduce the filament voltage by a relatively small amount, say .1V. if the filament is capable of oversupplying electrons at 6.3V, reducing the fils to 6.2, should still supply enough electrons for the normal operation of the valve.

So the LIFE TEST is testing the filament? or the filaments voltage?

Why doesn't this Digital Tube Tester test this?

Gm is short for mutual conductance (1/R), or if the grid volts changes by 1V how many mA the anode current changes by. With push pull output stages, while the anode currents could be equal between the valves, they could change by a different amount for the same voltage changes on their grids.

So if the Tube has BAD GM conductance , what does this mean? the tube doesn't have much gain or the output of the tube is low?

I use to test tubes on an Analog tube tester, it just tested the Emission of the tube

The Digital Tube Tester tests:
1.) Transconductance which is GM?
2.) Plate Current

An Analog Tube Tester doesn't test a tubes Plate current right?

It test the Tubes plate voltage either at 350v or 400v, an analog tube tester doesn't test tubes plate voltages at this its at 25 volts or lower right?

Does analog tube tester bias power tubes at -60, -48, -36, -24, -14 ?

 

[chuckey]

"So the LIFE TEST is testing the filament? or the filaments voltage?" Filaments get hot and heat the cathode, the cathode is coated with special chemicals that emit electrons at a low temperature. These chemicals slowly " boil" off, so the only way to see what life is left in the valve, is to somehow test how much of these chemicals remain. With a new valve there could be twice a much compared to what is needed for it to get its rated anode current. With an old valve, this margin falls. so to test this margin, you drop the filament voltage and see if the rated current can be got. If the rated current can not be achieved with the rated filament voltage, the the valve is suffering from "low emission" . Years ago when black and white TV cathode ray tubes were expensive, it was common to fit a booster heater transformer with taps on it for 6.3V +5% and +10% to get the emission back to drag another years life out of the tube.
Frank

 

[danny davis]

So the LIFE TEST, is testing the Cathode? cathode's chemicals?

Analog Tube tester
1.) Test The Grid Emissions
2.) Test the Grid Leakage