NOS tube supplied with Eros

A

alejon

New member
Hi all,
I've got a calibrated B&K 747B tube tester.

When I test the NOS 6N23P tube supplied with the Eros kit (using 6DJ8 pin/test settings), it shows only 60-65% for both halves while the "good" green scale is from 65 to 120%

Is there any issue with this tube? What is acceptable test value?

I've tested few other 6N23P tubes to 90-100%

Many thanks in advance!
Best regards,
alejon

 
Have you tested it in the Eros circuit? What voltage reading did you get?
 
Dear Doc B.,
No, haven't tested in circuit yet, just rolling tubes in the tube tester (new thing up here)
It is a dynamic mutual conductance tube tester, so it supposed to be OK.
While some other used 6n23p's test GOOD the one from the kit hardly makes it in  the OK region, and it looks NOS.
Just curious.
Regards!
alejon
 
It can also help to look at the settings on your tester for a 6922 and 6DJ8, and see what variations there may be in the test setup.  I know on a TV-10, the settings are quite different.

The best test of the tube is to run it in the circuit.
 
Hi Paul,
Yes, sure the settings are different for the ECC88/6DJ8/6N23P and for the 6922 (since they are not exactly the same tube)

I am comparing "same" tubes using "same" settings (6DJ), so it still should give an indication.

I am just curious how bad a NOS tube can measure?

How long burn in period a NOS tube may require?

Thanks again! Regards,
alejon
 
Tube testers are a quick and easy way to test large batches of tubes. The good/bad cutoff point is somewhat arbitrary because different tube testers use different operating points for tests and test different things. Tube checkers, emission testers and transconductance testers all do different types of tests. And between testers that do the same test, different models use different standards for operating points and go/no-go conditions. We test the tubes before we put them in kits with a TV-10 B/U, which is a tester that the military used a lot. The bottom line is that how the tube measures and how it sounds in the amp circuit is what matters. If one snuck by us and you got a bad tube that doesn't measure right in the preamp, we will replace it. But you don't know if you have a good or bad tube until you build the kit, test it in circuit and listen to it. Sometimes a tube just needs to run for a while to form the cathode so that it emits electrons at its full capacity. And sometimes a tube can measure perfectly new but have noise problems, or die within the first ten hours of operation. That's just life with vacuum tubes.
 
Dear Doc B.,
Thank you for the reply! Yes, I fully agree.

While I still have you on the line - and just for my own understanding (regardless to Eros).

If a tube shows large difference between the halves, let's say 45%, is this a good reason to reject this tube from using in the circuit?

Thank you in advance!

Regards,
alejon

 
What kind of large difference? Gain? Emission? Transconductance? Plate voltage? Heater glow? Do you mean some difference measurable when the tube is operating in the intended circuit? Which circuit? Voltage amp? Cathode follower?

You really have to define the situation and choose accordingly. In Eros a gain mismatch in a 6922 might be audible. Or it might not. It might also be easily corrected by swapping EF86s, as they may have a slight mismatch that could even out with the 6922 mismatch (ask me how I know). And it may or may not show up in a transconductance test because it may be operating differently in the tube tester than in the Eros circuit.

In some push-pull circuits and some parallel single ended circuits it is very important to have even current draw between the two tubes. In SE amps with a single output tube it's not such a big deal.

In cathode followers the gain is typically less than unity and in an amp like the Crack the fact that 6AS7s and 6080s (which run as cathode followers) are seldom well matched is insignificant.

I get that you are asking for a defined go/no-go point. But it's just not that simple.
 
If a tube shows large difference between the halves IN THE TUBE TESTER, let's say 45%, is this a good reason to reject this tube from using in the circuit?

B&K 747B is a dynamic mutual conductance tube tester.

Regardless to Eros or any other circuit.
 
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