I'm guessing these loudly humming ANOS 6L6GBs are now worthless?

KissTone

Silver Supporting Member
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3,008
I've had a pair of really clean ANOS GE 6L6GB's that I picked up by chance years ago but never had an amp that used them . . . until now . . .

Recently acquired a RI Bassman through the Emporium and thought I'd try these GE . . . popped them in and they sounded GREAT for all of two or three minutes and then a deep, powerful hum overpowered everything. :(

Put the old GT tubes back in and the hum was gone (but the crackling on warmup returned--but that's a different story).

I have a basic B&K DynaQuick tester which reports both GE tubes are fine . . . but clearly they aren't.

Just toss 'em?
 

gldtp99

Member
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4,291
6L6GB Data Sheet:

https://frank.pocnet.net/sheets/049/6/6L6GB.pdf

The max voltage rating is 360V for the plates and 270V for the screen grids.

Putting old 6L6GB tubes in a modern amp that is designed for 6L6GC type tubes and has typical 6L6GC voltage levels will quickly ruin the older spec 6L6GB tubes.

This is what you have done.

You say they sounded great for two or three minutes.

Those 6L6GB's would, most likely, have had a long and happy life if operated under the conditions they were designed for. :(:(:(
 

Tron Pesto

Silver Supporting Member
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920
Did you rebias the amp for the 6L6GB’s?
I doubt re-biasing would have helped - the plate and screen voltage is just too high, independent of what current is being drawn. I would bet the screens blew - they are the most sensitive and probably don't come into play in an emissions tester which is why the tubes still read as "good" on the tester.
 

Muttlyboy

Gold Supporting Member
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2,998
I recently learned a similar lesson.
A few years ago, I got myself a pair of NOS 5881s for a "special" amp, and I never really ran the amp.

I got a very nice Top Hat amp (Super Deluxe runs at 380v, and worked out to about 46ma on each tube) recently, and put those special 5881s into my newly acquired amp, and the tubes died in about 15 minutes.

My lesson learned is to run those tubes immediately when you get them, so if they fail right away, I may have a leg to stand on when I ask for replacement .
 
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1,657
My lesson learned is to run those tubes immediately when you get them, so if they fail right away, I may have a leg to stand on when I ask for replacement .

That's lame.

Your approach is to blast a perfectly nice pair of vintage tubes above their designed maximum tolerances, so you can replace them when your own folly causes their meltdown?

Any vintage tube seller who is generous enough to even offer a warranty is facing a sizable liability in the first place.

The market is already full of ignorant buyers who don't understand tube specs and make honest mistakes, so I don't understand why you would willfully promote careless experimentation, just to take advantage of an honest seller's return policy.
 

Muttlyboy

Gold Supporting Member
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2,998
That's lame.

Your approach is to blast a perfectly nice pair of vintage tubes above their designed maximum tolerances, so you can replace them when your own folly causes their meltdown?

Any vintage tube seller who is generous enough to even offer a warranty is facing a sizable liability in the first place.

The market is already full of ignorant buyers who don't understand tube specs and make honest mistakes, so I don't understand why you would willfully promote careless experimentation, just to take advantage of an honest seller's return policy.
I'm pretty sure that didn't run the tubes past the max tolerances.

Cathode biased amp, 380v, at a bit under 18 watts each.

I bought another pair from a different vendor that I've had good experience with, and he told me that 18 watts , cathode biased should be fine.

The new pair seems to be running fine.

But Hey, thanks for your kind concern.
 

HotBluePlates

Member
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13,599
... I have a basic B&K DynaQuick tester which reports both GE tubes are fine . . . but clearly they aren't.

Just toss 'em?


I'll take them off your hands!

I'm actually curious if they are problematic, and how that hum problem would show up on my new tube tester.
 
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1,657
I'm pretty sure that didn't run the tubes past the max tolerances.

Cathode biased amp, 380v, at a bit under 18 watts each.

I bought another pair from a different vendor that I've had good experience with, and he told me that 18 watts , cathode biased should be fine.

The new pair seems to be running fine.

But Hey, thanks for your kind concern.

I wasn't referring to your personal story (note that I didn't quote that part).

I was referring to the [advice] you were giving as it pertains to the context of this thread.
 
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1,657
So does that mean the tubes are toast?

By "fault" he is suggesting there is a short between the heater and cathode, which yes, would mean one or both are toast.

Your DynaQuick should be able to test for shorts, but did you run a shorts test or just a conductance/emissions test?

If your tester has a Fuse Lamp, it may or may not be triggered by a short, but often a tube will still show good conductance even if a short exists (and can sometimes damage a tube tester, which is why a shorts test should be performed prior to a conductance test).
 

Muttlyboy

Gold Supporting Member
Messages
2,998
I wasn't referring to your personal story (note that I didn't quote that part).

I was referring to the [advice] you were giving as it pertains to the context of this thread.
I guess the way I told my story, I wasn't very clear .

My lesson learned is that when I buy tubes, I should test them in the intended amp (that is known to be in good working order) running within the proper recommended current/volts/watts.

If the tubes fail immediately, I may have a fair position to ask for replacement or refund.

If I put the tubes away on a shelf, and finally use them several months (or more) later, there would be no way I could ask for any kind of replacement.

If the tubes are sold "as-is-all-sales final- no backsies-no-stories-no-nuthin", then of course, that would have to be understood.

I would also think that for a vendor to entertain the idea of replacement, he would ask what current/voltage/watts you were running the tubes at, etc.

I did not mean to suggest to people to go ahead and abuse the hell out of new NOS tubes to the point that they burn up, and then go ahead and expect a bail out for irresponsibility
 

KissTone

Silver Supporting Member
Messages
3,008
By "fault" he is suggesting there is a short between the heater and cathode, which yes, would mean one or both are toast.

Your DynaQuick should be able to test for shorts, but did you run a shorts test or just a conductance/emissions test?

If your tester has a Fuse Lamp, it may or may not be triggered by a short, but often a tube will still show good conductance even if a short exists (and can sometimes damage a tube tester, which is why a shorts test should be performed prior to a conductance test).

Yes, it has a “short” bulb, but it didn’t light up for either tube when tested after the humming incident.
 

MKB

Silver Supporting Member
Messages
9,142
FWIW, I had a similar thing happen a few years ago with a pair of those straight envelope Russian 6L6's like Groove Tubes used to sell as 6V6's. I put them in a mid 70s Bassman head and they hummed a bit, and would not bias correctly. I jerked those and put in a set of 5881's, and those worked fine.

Those "6L6's" still tested properly though after they seemingly failed in the amp. And as I recall they worked properly in a Mac MC30 (designed for original 6L6's). Perhaps there is a B+ or bias related condition that will pop up when the tubes are operated outside their parameters, but no permanent tube damage is done.

It would be nice if tube sellers would educate customers on the differences with 6L6's over the years so they do not put early ones in amps designed for newer, higher spec ones. When you compare the maximum operating limits of an original 30's 6L6 to some of the later builds like the STR's, there's a huge difference.
 

HotBluePlates

Member
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13,599
... It would be nice if tube sellers would educate customers on the differences with 6L6's over the years so they do not put early ones in amps designed for newer, higher spec ones. ...

That's an impossible dream, because for the past few decades vendors have been putting every type of label for every 6L6-variant on every kind of tube, regardless of its max ratings.

It's why few seem to grok the differences between the various suffixes applied to "6L6," the different industrial type numbers, the various markings for military tubes (and how those convert to commercial type numbers), etc. If you're looking at a 1980's or earlier tube, those different marking imply different specs, but 90's & beyond anything might have any marking.

It makes understanding the specs less relevant for most players today. (That, and the fact that you probably can't trust any current manufacturer's data sheet, if they even publish one.)
 

tbonesullivan

Member
Messages
1,269
This would be why I don't even touch "old-stock" power tubes. Heck even the Siemens / RFT EL34s can go up in smoke if you put them in a lot of "modern" amps, as they don't like over 450V on the plate. Kinda makes me wonder why Mesa boogie even sells them, considering most of their amps are over 450V on the plate, particularly the EL34 ONLY Stiletto series, at 468V. And, there are also quite a number of amplifiers designed over the decades that ran tubes over spec, mostly with EL84s if I remember correctly.
 

Dan40

Silver Supporting Member
Messages
1,884
It was asked above if you properly biased the tubes before playing? If not, the hum that you heard may have been the tubes redplating and drawing an excessive amount of current. Did you notice any signs of redplating before shutting the amp down?
 




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