plate current meter...build

[Garydean]

When building a plate current meter, do I put my binding posts in series/in circuit at the cathode, pin 8 for octals using pin 8 as the cathode. My adaptor will be used in conjunction with a tube tester. I will be plugging in the tube on my adaptor and running a home-made lead with an octal plug which will plug into the tester. I'm looking to measure plate current. My DMM will measure plate current at the binding posts.

thank you.

[Alex R]

Not entirely sure of your aims. Ammeters generally go in series in a circuit, so the current passes through the meter (shunts notwithstanding). Putting an ammeter in series at the cathode will give a total current figure through the tube including the screen current and anything else trying to get to ground through whatever element. An ammeter in series at the plate will give you the plate current. However tube testers don't always run tubes in normal ways. Plate volts for instance might be quite low, and currents atypical.

[Garydean]

Thanks Alex. I'm trying to test idle plate current of 6L6 type tubes, with a tube tester. I've found out it won't work using a Sencore MU-150. I do have a Hickok 752 that I haven't tried it with yet. My aim is to use this method to match output tubes. Is this possible? Are the voltages too low? Can I only match by testing cathode current?

Gary

I have an Alessandro plate current tester which I also use with my Sencore and I get proper readings. Does that measure cathode current?

[Garydean]

Just a thought. I built a "Champ design" amp last year and I don't use it. It's just a chassis sitting on a shelf now. I would be able to match 6L6's but what changes would I need to make if I tried to test 6550, 6V6 and other octal output tubes. Could I build a tube tester from this champ to satisfy all popular octals?

[Garydean]

Thinking about my last question a bit.
I guess it wouldn't work as I would need to apply different voltages to each type of tube under test. The transformer I have in there supports only one tube type.

[Bruce / Mission Amps]

Just a thought. I built a "Champ design" amp last year and I don't use it. It's just a chassis sitting on a shelf now. I would be able to match 6L6's but what changes would I need to make if I tried to test 6550, 6V6 and other octal output tubes. Could I build a tube tester from this champ to satisfy all popular octals?

This exactly what I have and although SE class A...it also has a variable bias supply so I can move the tube being tested up and down in idle current to see how it reacts. Comparing various power tubes like this reveals quite a bit of good current matching info.
Then taking the tubes over to my big Hk 539 tester gives me more mu data to work with.

[Garydean]

Thanks Bruce... so you just pop in any octal with the same pin-out and take idle current readings? This amp has no bias adjustment..... I should install one?

Gary

[Garydean]

Food for conversation.... if I had the room, or a larger chassis, and as long as I don't use this amp as an amp (no signal), would I be able to parallel 3 more 8pin sockets and use it as a tube matcher? Then I would need 4 meters. Could I disconnect the preamp?

Or.... leave it as is (one output tube) and inject a signal to observe tubes closer to a real life situation? Using a dummy load of course.

just curious...