Tung Sol 6V6 Reissue consistent problem

[Wil]

Hello everyone,
I first want to say I had the same problem with two different sets.
The tubes sound great when I use them the first time, they're well biased (0.02mA in this case),etc The amp (a DRRI) sounds gorgeous... But then, let's say I go to eat and I come back after that, I turn the amp on and the tubes look like they're mismatch, I read 0.017mA on V8 and 0.024mA on V7. Worse, when I crank the amp up, after that, I measure things like 0.006mA on V8 and 0.025mA on V7.
Numbers aren't what's bothering me, it's the sound of the amp. Duller, less definition,... I only get to know how a DRRI should sound on the first time I play the tubes.
If anyone has a clue, it would be greatly appreciated!
Thank you.

Edit : Just checked all voltages from the Power tubes, they're all fine according to the DRRI Service Manual.

[nickb]

Does the problem follow the tubes? Note which has the higher current, swap and repeat. Did the high current swap over too?

[Dave Curtis, dB AudioTech]

Just to clarify: .02 mA is a very small amount of current. I'm assuming you mean .02 A, which is 20 mA.

What are the bias voltage readings per tube as the current draw fluctuates? If it's staying steady, then your new tubes are drifting, and probably haven't been burned-in prior to matching. If it's fluctuating also, you need to pinpoint why.

[Enzo]

What Dave said.

Warm up is important. Tubes need to be fully warm before adjusting bias. As they warm up they will wander around. You want to watch so they don;t run away, but let them go 20 minutes before expecting stable adjustments.

[Enzo]

What Dave said.

Warm up is important. Tubes need to be fully warm before adjusting bias. As they warm up they will wander around. You want to watch so they don;t run away, but let them go 20 minutes before expecting stable adjustments.

[Wil]

Yes it does, let's say V7 reads 0.007A, if I swap, V8 then reads 0.007A. (to be clear, haha)

[Wil]

Sorry I spotted my mistake a little too late, yes it's 0.02A and not mA.
I may have gone a little too fast the first time, I let them warm up for only 3/4 minutes. But now, I can let them warm up for 30 minutes, the closer they could get was a difference of 0.007 (V7 0.017A V8 0.024A), but each time I play the amp, the difference in current between the two tubes gets worse. Each time I crank the amp up, the "defective tube" goes lower in current. Do you think it made irreversible damages to that tube ?
Bias voltage are correct (if I remember well it was approx -30V on pin 1, -45V on pin 2, and -60V on pin 3, or the opposite, I don't really remember, haha)

EDIT : Plate voltage goes from 380 to 420V.
Current draw of the "normal" tube goes from 6.1mA to 52mA
Current draw of the "bad" tube goes from 4.6mA to 35mA.
When the normal tube is set at 21mA, the bad tube reads 13mA (forgot to measure the plate voltage at the time, sorry but I guess between 396 and 440V is fine).

EDIT 2 : After powering the amp (waiting for about 1 to 2 minutes) when I switch the standby on, when the bad tube warms up, there's a small metallic ticking sound, which frequency rate lowers as it warms up.

[Tom Phillips]

...Bias voltage are correct (if I remember well it was approx -30V on pin 1, -45V on pin 2, and -60V on pin 3, or the opposite, I don't really remember, haha)...
...EDIT : Plate voltage goes from 380 to 420V.
Current draw of the "normal" tube goes from 6.1mA to 52mA
Current draw of the "bad" tube goes from 4.6mA to 35mA.
When the normal tube is set at 21mA, the bad tube reads 13mA (forgot to measure the plate voltage at the time, sorry but I guess between 396 and 440V is fine)...

Will,
You have several goofy readings here. I suggest that you check again when you have time and can accurately record both the measurement conditions and the exact values measured. Then the forum members can better help with troubleshooting. I think this may all come down to a bad 6V6. However, reports like "-45V on pin 2, and -60V on pin 3" sound like you may be using the wrong point for ground reference, getting the pins mixed up or something.
Tom

[Wil]

Will,
You have several goofy readings here. I suggest that you check again when you have time and can accurately record both the measurement conditions and the exact values measured. Then the forum members can better help with troubleshooting. I think this may all come down to a bad 6V6. However, reports like "-45V on pin 2, and -60V on pin 3" sound like you may be using the wrong point for ground reference, getting the pins mixed up or something.
Tom

Don't take the bias pot voltages too seriously, I don't remember them nor at what "bias stage" (I mean 22mA on the tubes) I measured them.
I'm sorry but some of my goofy readings might come from the fact english is not my mothertongue.
The tube is defenetly defective... But I wonder why, twice in a row, the same thing happenned...
What makes only one tube go bad ? The other one works like a charm...
The defective one, if I play it cranked, it looks like it's out of breath, it needs minutes of silence to get back to the bias setting it was set...

[JoeM]

Oh, so you were referring to the bias pot pins, not the power tube pins. I couldn't figure how you had negative volts on pin 3 for example.

Does this problem only happen with the Tung Sols?

[Wil]

Oh, so you were referring to the bias pot pins, not the power tube pins. I couldn't figure how you had negative volts on pin 3 for example.

Does this problem only happen with the Tung Sols?

I should have said lug instead of pin for the pot... sorry !
Yes it only happens with the Tung Sol's, I just put back the JJ's biased at 27mA (quite hot), about 75% of maximum plate dissipation.
I also put a DPDT switch to have to Negative Feedback on or off and wow... When it's off, the amp really sings, it's amazing... It has the same sound, with the JJ's, that the amp had with the Tung Sol's but with the NFB wire on... Incredibly easy and effective mod !

[JoeM]

Sounds like a bad tube(s). Happens I guess. I have Tung Sols in my DRRI and they sound nice, want to try the JJs too. But why such a hot bias?

[Wil]

Sounds like a bad tube(s). Happens I guess. I have Tung Sols in my DRRI and they sound nice, want to try the JJs too. But why such a hot bias?

I don't think it's that hot to me, 394V*0.027A = 10.63W, The Deluxe is supposed to be a 22W so 21.2W feels and sounds nice to my ears :-) !
The funny thing is I already sent back a set of the exact same Tung Sol's which had the same problem so I wonder: Should I have make them warm longer before my first use ? Am I that unlucky ?
It seems like the problem starts when the tubes cool down for the first time. Because when I put them in the amp, they sound absolutely great, but when I want to play the amp again (let's say a couple of hours later) the problem pops up...
Thanks for your input, indeed !

[loudthud]

Check the tube socket and re-tention the contacts. A loose pin on the heater can cause plate current to fluxuate. Some tubes have oversized pins that cause loose contacts and make sure the tube pins are bright and clean.

[JoeM]

I don't think it's that hot to me, 394V*0.027A = 10.63W, The Deluxe is supposed to be a 22W so 21.2W feels and sounds nice to my ears :-) !
The funny thing is I already sent back a set of the exact same Tung Sol's which had the same problem so I wonder: Should I have make them warm longer before my first use ? Am I that unlucky ?
It seems like the problem starts when the tubes cool down for the first time. Because when I put them in the amp, they sound absolutely great, but when I want to play the amp again (let's say a couple of hours later) the problem pops up...
Thanks for your input, indeed !

Do what loudthud suggests, if you've had this problem with more than one set.

Have you tried a cooler bias? My DRRI (with Tung-Sols) loses high end and string definition with too hot a bias, but maybe your pushing your amp more.