Western Electric 300B testing predicament

Daniel P-O

Daniel P-O

New Member
So recently a customer sent me a number of Western Electric tubes to test and pair. I have a Hickok 800 tester, and was able to test the 12 350Bs, and the lone 274B, but I'm having a problem figuring out the settings to test an original 300B.

I have the supplements to the Hickok 800 instruction manual (both the Obsolete Tube Types and the Foreign Tube Types), but I can find no settings for the 300B. One suggestion I saw elsewhere was that you could test it according to the settings for a 2A3 tube (which settings are in the obsolete list), but the filament setting would be 5 instead of 2.5. I haven't been able to verify that anywhere else though. I have the spec sheet for the 300B, but I'm not skilled enough to deduce the settings on the Hickok from the spec sheet.

Does anyone have any suggestions?
 
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The TV7 manuals should have the settings for the 2A3 and the 300B. Hickok often made the test conditions different from model to model for inexplicable reasons, but you should be able to compare the TV7 settings to the 800 settings for the 2A3 and extrapolate from there.
 
Daniel P-O said:
So recently a customer sent me a number of Western Electric tubes to test and pair. I have a Hickok 800 tester, and was able to test the 12 350Bs, and the lone 274B, but I'm having a problem figuring out the settings to test an original 300B.

I have the supplements to the Hickok 800 instruction manual (both the Obsolete Tube Types and the Foreign Tube Types), but I can find no settings for the 300B. One suggestion I saw elsewhere was that you could test it according to the settings for a 2A3 tube (which settings are in the obsolete list), but the filament setting would be 5 instead of 2.5. I haven't been able to verify that anywhere else though. I have the spec sheet for the 300B, but I'm not skilled enough to deduce the settings on the Hickok from the spec sheet.

Does anyone have any suggestions?
Click to expand...

You can go to this link and download the basic Hickok setting for WE tubes:

https://plymouthcolony.net/starcity/radios/pages/service.html#hickok

On my 533 it's

Filaments 5V

JR 3200-0 Bias 60 English 87 reading 4600

Seems to work pretty well. Should work on the 800. I've also seen:

JR 3200-0 Bias 25 English 88 reading 4000

ETA: Kyle beat me to it! ;-)
 
Kyle, Zack, Sam:

Thank you so much for this. It's a huge help. I'm still learning. I really appreciate your help. I'll let you know how it turns out.
 
Kyle and Zack,
Thanks again for the info. The settings in the supplementary data for the Hickok 600 worked well with my 800.

Unfortunately for my customer that 300B he sent didn't test well. 2780 uohm and 62mV. Definintely in the questionable zone if not outright bad. But he's got 12 350Bs which are pairing pretty nicely, so it's not all bad news.
 
TriodeLuvr said:
Not to insult your intelligence, but these tubes also need full voltage and current applied in order to be correctly matched as pairs. I use a Hickok too (for other power tubes), but it's only one part of the process.

Jack
Click to expand...

No, you're not insulting my intelligence. As Brian Wilson said, "they say I have brains but they ain't doin' me no good." :)

But, seriously, that's a good point. I was told yesterday that the customer has shipped us the amp itself, because the meter(s) need(s) fixing.
So once we get that, I guess I can do a proper test of the sort you're talking about.
 
Shawnnnn said:
What Jack said.

Given the huge value of those 300b's I'd want to test them with another tester to be absolutely sure they aren't good.
Click to expand...

Good point. I don't have a second one except for a Heathkit I haven't calibrated yet. I'll ask a friend who lives nearby; he should have one.
 
Daniel P-O said:
No, you're not insulting my intelligence. As Brian Wilson said, "they say I have brains but they ain't doin' me no good." :)

But, seriously, that's a good point. I was told yesterday that the customer has shipped us the amp itself, because the meter(s) need(s) fixing.
So once we get that, I guess I can do a proper test of the sort you're talking about.
Click to expand...

FWIW, I tested a large number of power pentodes years ago for the purpose of matching pairs. These were 6L6 variants. They were graded on my Hickok first for Gm, then I plugged them into a push-pull test amp, four at a time, and measured idle current. Some time after that, I pulled a number of pairs from this stock and was disappointed to discover that much of the work had been in vain. I had set up a (different) amplifier on the bench with a spectrum analyzer for the purpose of assessing balance by means of 2nd harmonic distortion. It turned out that most of the pairs weren't actually balanced very well for gain. My conclusion was that Gm as measured on a typical tube tester isn't particularly useful in matching power tubes, as it changes at the higher voltage and current with which the tubes will eventually be used.

How this might translate to a pair of 300B tubes used single-ended, I'm not sure. Gain balance is probably somewhat less critical, because it's not a factor in cancelling harmonics. Then again, spectral characteristics affect the tone, so I might want to include that in any attempt to produce near-identical pairs. It's something I would have to try to know whether it's important.

One more thing - plugging and unplugging all those tubes in the customer's amp might not be the kindest thing for its sockets. Most aren't made to withstand that type of use.

Jack
 
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