borrowed a Hickok 752 - not sure whether to be happy with measurements or sorry I started measuring

[Murrayatuptown]

I borrowed someone's Hickok 752 to measure gm on some tubes I bought many years ago. All were 'NOS'.

I wasn't sure how meaningful or accurate my measurements would be....so I took some new (Sovtek...but are they really what they are marked as, or close subs from the Soviet versions?), some old and a wide variety and took notes.

I was pleased some dual triodes actually had very nearly identical gm between sections, others were disappointingly not so, and some tubes I knew were very old and well used did indeed read poorly.

No idea if it's 'calibrated'. I set the line voltage to the mark, let the tubes under test warm up & when the meter reading stabilized, that's what I wrote down.

Would these testers 'naturally' read low due to aging, or differently due to higher line voltage than when they were made?

A batch of very old NOS ECC88/6922's nearly all were well matched, but all were lower (10750 uS or so) than datasheet value (11250-12250 uS)...but I don't know what the test conditions in the Hickok were, vs. datasheet.

I had one very old and used 7308 that was surprisingly high, about 16000 on the first section, and I hadn't figured out the simple two button method for measuring the 2nd section, and forgot to measure the 2nd one.

I will never use the 6922's, and should sell them (with a bottle of antacid in my hand, as I see how the audiophile folks can be). I'll be happy to keep a few mismatched ones for cascode experiments as I couldn't care less how close they are.

Not having measurements is undesirable, but having them doesn't make me feel much better.

I even see some tube sellers say to not even bother with antique tube checkers, other than to make sure they aren't garbage.

I borrowed the 752 because I 'only' have a BK Precision 6xx (don't remember...maybe 606) and I thought its non gm emission measurements were pretty vague.

I'm not even sure I'm even asking a question...because I don't know if there is an answer other than 'relativity.

:O(

Thanks for any thoughts, advice, even snickers...

Murray

[Murrayatuptown]

6080's were a joke...the lamp 'fuse' glowed brightly, probably because they are such filament current hogs, I had to really 'ride' the line voltage pot, and mu is supposedly pathetically variable on these, between tubes and sections...so I guess gm could also be and those read lower than datasheet for gm too (also NOS).

[Murrayatuptown]

...and I'm not the first to discover the 752 predates the 6267/EF86...so no chart settings.

[Murrayatuptown]

correction:

7308 first section did not measure 16000 for gm; it was 13750.

[Scumback Speakers]

I've got a Hickok 6000A. It had to be gone through, new VU meter, couple of new sockets, and then calibrated to be accurate and useful. Lucky there was a guy in Torrance, CA that specialized in this stuff, so it's all good now.

[xtian]

Murray, are you coming from the hi-fi world, where folks are about matched triodes in 12A?7 packages, or the guitar amp world, where most (me, specifically) don't care if the triodes are matched? Because it's FAR easier to use your ears than it is to calibrate and test and then use your ears.

[Phil_S]

If you are interested in using today's technology to test gear from another century, look at the µTracer.
Thread here at TAG: https://ampgarage.com/forum/viewtopic.php?f=17&t=31549
Website: https://www.dos4ever.com/uTracer3/uTracer3_pag0.html
Relatively inexpensive, but requires the ability to assemble and use the kit.
If you have deep pockets, look at the Amplitrex!

[Murrayatuptown]

Was from hifi world, deaf in one golden ear now...just joking about the golden ear...never finished my own hifi builds, now interested in building guitar amps...used to repair tube gear at Heathkit 1989-1991, and various industrial gear, so I won't become a victim of undesired conduction...leaning toward peculiar circuits from yesteryear, including the infrequently seen cascode well illuminated by Merlin Blencowe & Ulrich Neumann...I don't need 'collectable' tubes...garden-variety 6DJ8 and 12AU7 are fine for cascode. I will definitely be exploring some traditional Fender and Gibson circuits, too, and some inspiring schematics posted by the likes of PRR, SLuckey, Tubenit and many others.

I'll just be patient and endure the eBay questions and doubts about where the getter minerals were mined and what phase the moon was in during said mining, and of course the ever-present suspicion of counterfeit & remarked goods. I'll ditch the tubes that are a waste for my needs to fund other projects.

I was just lamenting the frustration of having tube measurements vs. not. Oddly, those two situations can be similar. Plenty of people selling stuff are ambiguous anyway "tests NOS", "tests strong", etc.

I like the idea of using a circuit that does what one wants, as a test platform for audible tests. If the tubes are in your own hand, your own assessment is all that matters.

Thanks for enduring my frustration. I returned the 752, glad it's not mine to maintain.

I have a TV3-B/U, IIRC, with an open meter movement...not even sure where the meter is this decade...I'll probably put a resistor in place of the meter and use a DMM & a calculator...

Oh, Ron Dekker's DOS4Ever site & uTracer...yes, I am on his mailing list...inspiring but I should probably finish a project or two before going down that path.

[Murrayatuptown]

and I love Phil S' Pointy-Haired Boss avatar.

Also reminds me of Gary Larson's The Far Side...Mac the Knife, Bob the Spoon & Ernie the Fork. I incorrectly recalled myself being Murray the Spoon, but I was apparently one of the Grizzlies from Hell dreaming of trying to restore an abandoned car in the woods...

[Murrayatuptown]

Antique Radio Forum has a lot of discussion about 6DJ8 having legendary lack of cooperation with Hickok testers...my readings are higher than many other people's, so I'll take that as lucky. They did not know why there was a problem, but suspected test circuit, or wrong settings in chart.

Murray's Law...but there was a recommendation for a manual test setup with instrumentation.

[Phil_S]

and I love Phil S' Pointy-Haired Boss avatar.

Murray: it's Phil, the prince of insufficient light from Dilbert.
https://dilbert.fandom.com/wiki/Phil,_t ... ient_Light

[Murrayatuptown]

Thank you.

[Doug R.]

There are pdf files online at bama.edebris.com for the 752 tube tester...alignment, etc.

I have owned one for 50 years..

[Doug R.]

Go to stevenjohnson.com

[Murrayatuptown]

Thank you, Doug.