B&K Tube Tester & output tube question

[Chevy]

Hi,
I've got a small B&K 606 Dyna Scan tube tester, using it recently for testing 6L6's. When I do the "shorts" test (you rotate the last knob to about 12 different positions or so), I get a short glow of the "short" lamp on position 10, then it goes away. It's not a transient flash like I see in several positions, but it actually stays glowing dully for a few seconds, then seems to dim and go away.

I don't follow how a "short" could behave like that in a tube. In the past, I seem to recall, I've also received a few NEW Ebay-sold 6L6 tubes that behaved the same way. As a matter of fact, I think they continued to glow the "short" light, if I remember right, in position 10 again, but very dimly. I expected a true short to cause the lamp to glow full tilt.

What does this mean?

[Enzo]

I think it means we place to much emphasis on lights and meters. DO those tubes work in amps? I have no idea what test #10 is looking at. There is enough leakage current to allow the neon indicator - it is neon isn't it? - to glow between two places in the tube. May not be relevant in the real world.

[Chevy]

Yep, it's neon..... haven't tried the tubes to prove out anything... more of a concern that I wanted to resolve one day.
Thanks.

[Marc]

Chevy,
I'm with Enzo, testers are OK but not really a good measurement device for our purposes. They typically measure around 200V +/- 50V and that's not 'real world' to the voltages they see in guitar amps. Even when these testers are calibrated and have a known standard tube to measure they are not perfect.
The instructions in my dyna 707 say the shorts test is made to a sensitivity of about 1 M ohm. If there is a drifted resistor (or two) in your tester it could concieveably throw off that position. If it were truly shorted the glow would not fade away.

Marc

[Mars Amp Repair]

As Marc states, you'll get a better test by how tubes function in the circuit or just merely by substitution.
I have an Eico 666 & I was only wanting to use it for emissions testing as the rest is better determined in circuit, but I can see that I really can't even rely on the tester for emissions as if the dial for grid bias is just a hair out of position, the emissions reading can vary nearly 1/4 of the scale of Bad to Good.
I think if there were a meter on the tester to actually measure the grid voltage your setting the knob to, then it might be useful.

So what's the tester good for?...haven't figured it out yet, but my techs really like it.

I guess as an old tube TV repair guy, when I was verrrrry young mind you ;-] , I got used to tapping & substitution over testing. glen

[Garydean]

Check R-5 which is a 10M resistor. That may be out of spec. While you're in there be sure R-7 is within 5% of 500 ohms as well as R-8 is at 47 ohms or within 5%. C-3 is probably original and should be checked as well as C-1. Not much to those so calibrating is easy. Check or replace V-1, 6BN8.

just a thought.

[Chevy]

Originally Posted by Mars Amp Repair

As Marc states, you'll get a better test by how tubes function in the circuit or just merely by substitution.
I have an Eico 666 & I was only wanting to use it for emissions testing as the rest is better determined in circuit, but I can see that I really can't even rely on the tester for emissions as if the dial for grid bias is just a hair out of position, the emissions reading can vary nearly 1/4 of the scale of Bad to Good.
I think if there were a meter on the tester to actually measure the grid voltage your setting the knob to, then it might be useful.

So what's the tester good for?...haven't figured it out yet, but my techs really like it.

I guess as an old tube TV repair guy, when I was verrrrry young mind you ;-] , I got used to tapping & substitution over testing. glen

But what am I gonna do without those idiot lights?! You mean I actually have to think?! Aargh.....

[Chevy]

Originally Posted by Garydean

Check R-5 which is a 10M resistor. That may be out of spec. While you're in there be sure R-7 is within 5% of 500 ohms as well as R-8 is at 47 ohms or within 5%. C-3 is probably original and should be checked as well as C-1. Not much to those so calibrating is easy. Check or replace V-1, 6BN8.

just a thought.

Whoah..... way more than I thought anyone would come up with.... cool! Thanks - I'll print this out and get in there one day and tune up the tester.

And to the other guys.... yes, I won't be so cautious and reliant on the tester..... will stick the tubes in the circuit and see how they work (unless of course the tester tells me it's totally dead or something).

Interesting side note on this..... just repaired a Twin amp, and the guy had purchased all new tubes recently. The 12AT7's (by EH) all tested bad on my tester.... not one of the new ones passed the Quality test; didn't even register on the dial. But I have a coupla really old 12AT7's that test great. The EH's all work well in the amp, though...... go figure.

[Mars Amp Repair]

Hey Chevy,
I also have noticed that happens with the JJ 12AX7's on my tester. They function completely fine in circuit but when compared with the older ones in the tester, the emissions test is way down in the dirt. Not quite sure what that's all about.

If I can believe the settings on the tester, they want the plate at around 90V. That is substantially lower than most 12AX7's work in a standard ckt. They also want the grid voltage at about 7V.

Maybe if tested at a higher plate voltage it would move the idle point to a flatter spot on the load line & hence the readings would not be so touchy?

Who knows...as I mentioned, I don't use my Eico 666 tester that much for those reasons.

I would probably use it for short/leakage tests if I were doing radio where shorts or leakage are not as obvious & I didn't have all those weird tubes to substitute.

Hope you get yours going ok...glen