international servicemaster 6l6gc

sector9

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I just got 2 of these from ebay. they have GT.BRITAIN stamped on them. anyone know anything about these, or where i can find some info?
 

Dutchman

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164
IS relabels, they are most likely Sovtec 6l6GC's. I've got a quad of 5881 IS tubes that are Sovtek 6L6GC's. They're still a very good tube....
 

Swarty

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1,130
Yes, Reflektor/Sovtec... thin glass, small bottle. The same tube that GT marketted as their 6V6HD through the '90s. I will disagree with it being a very good tube. I'd consider it a barely adequate 6L6.
 

Blue Strat

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30,686
What Swart said. If the glass is narrower than the base, they're the cheapest ever (in every sense of the word) "6L6" ever made. Likely, they're one of the many Russian "almost equivalent" tubes to US spec'd tubes. There were so horrible that Groove Tubes ended up marketing them as 6V6s because they were less likely to blow up in 6V6 amps than 6L6 amps.

FWIW, country of origin markings often mean nothing.
 

Swarty

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1,130
My guess is that GT marketted that tube as a 6V6 not because it was a crappy tube, but because the only 6V6 in production at that time was that Reflektor black bottle thing that was absolutely horrible. I don't know how many times I'd stick them in a Princeton Reverb or Deluxe Reverb and it would be instant fireworks.
 

Blue Strat

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30,686
Well Ive got a bunch of Internatinal Servicemaster 12AX7 Tungsram and RFT's. They seem to be defect free.

Right. Some are good brands and work fine. Half or more seem to be relabeled Russian, etc, with phony countries of origin.
 

Johnny Z

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144
I just got 2 of these from ebay. they have GT.BRITAIN stamped on them. anyone know anything about these, or where i can find some info?


I installed a set of 4 in my '75 Twin Reverb some years ago and they are still working very well, I'm the original owner of this amp and kind of picky about what goes in it. I test all the tubes in all my amps about once a year on a Sencore Tube Tester and these seem to be holding up well. If you can find any Westinghouse Made in GT Britian, 6L6's their the same tube, I have several of those as well, their getting hard to find, it's a good tube. I only found 2 out of the 48 I bought new in the early 80's that were defective and they worked but had emmision problems that made them noisy.

If they are new they should be very good, but buying then from ebay it's hard to say if they are new or used? Test them before you install them, and make sure they are good and have no shorts.

Good luck.
 

Johnny Z

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144
My guess is that GT marketted that tube as a 6V6 not because it was a crappy tube, but because the only 6V6 in production at that time was that Reflektor black bottle thing that was absolutely horrible. I don't know how many times I'd stick them in a Princeton Reverb or Deluxe Reverb and it would be instant fireworks.


Yep those black bottle 6V6's were bad. I still have several I woudn't even put them in a Crate amp. But they do work fine in old tube stereo's with lower plate voltages. I call them Stovetec tubes.
 

Johnny Z

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144
LABELED made in GT Britain, actually made in Russia. Yes, those are the same low end "6L6GCs".

Well they seem to be doing a good job in my '75 Twin. Never had one fail. I didn't think they would last more than a few years and I think there going on 8 years now. But then I don't gig that amp much any more and seldom push it hard. Guess I have lifetime supply.

How do they get away with the Made in GT Britain?
 

Blue Strat

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30,686
During the "Cold war" (if you're too young to remember, google it) the US did not trade with Soviet block countries. Since tube production in the US was on the downturn in the 1970s, some craft guys in Western Europe would import Soviet tubes, print "safe" countries of origin on them and sell them to US companies.

Nothing is ever 100%. Sounds like you got lucky with your tubes.
 

Johnny Z

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Messages
144
During the "Cold war" (if you're too young to remember, google it) the US did not trade with Soviet block countries. Since tube production in the US was on the downturn in the 1970s, some craft guys in Western Europe would import Soviet tubes, print "safe" countries of origin on them and sell them to US companies.

Nothing is ever 100%. Sounds like you got lucky with your tubes.

Yea these tubes are fine, I test every tube I get before I use it, learned that from my dad's TV repair shop. I bet some batches were bad.


Cold War, I remember it too well, I'm 57, the Korean war, The Cuban Blockade, the drop drills; like that was going to save us kids from a 500 mega ton H-Bomb. We even had a neighbor with a fallout shelter under their swimming pool. Nobody was supposed to know about it, but every kid in the neighborhood knew. We even got to see it because their kids showed it to us and we would go down there and eat the canned food.
 

Blue Strat

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30,686
"Duck....and cover".

The issue with tubes such as those is that they'll test fine in a tube tester (typically with no higher than 150V on the plates) but short out when installed in an amp, like a Twin, with 450V+ on the plates.
 

Swarty

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1,130
My issue with them is that their output was nowhere near 25w, more like 15w... Not necessarily a bad thing if you are looking for output tube distortion/grind, but certainly not a "real" 6L6GC. They are fairly reliable... I had some customers that loved them...one was a Boogie guy who just loved the way they broke up in his MKII... another was a touring band who played old school non-master Marshalls and when they came to me they were so poor it was all they could afford, they came back for more saying their Marshalls never sounded better. I think at the time I was getting them for $2.35.
 

Johnny Z

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Messages
144
"Duck....and cover".

The issue with tubes such as those is that they'll test fine in a tube tester (typically with no higher than 150V on the plates) but short out when installed in an amp, like a Twin, with 450V+ on the plates.


Several years ago I did a simple repair on my friends Bassman 100, he had just put 4 new Audio Glassic 6L6 tubes in, they didn't last a second, he turned on the amp, it blew the grid resistor on one socket and the fuse. After testing all 4 tubes 2 were bad. They looked just like the Westinghouse I have except it said Made in Russia. I put in 4 of my Westinghouse and it still workes fine today.

I'm begining to wonder if there was more than one factory making these tubes. Like I said earlier, I only found 2 out 48 that tested poorly and even they worked but I wouldn't use them.
 

Blue Strat

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30,686
Several years ago I did a simple repair on my friends Bassman 100, he had just put 4 new Audio Glassic 6L6 tubes in, they didn't last a second, he turned on the amp, it blew the grid resistor on one socket and the fuse. After testing all 4 tubes 2 were bad. They looked just like the Westinghouse I have except it said Made in Russia. I put in 4 of my Westinghouse and it still workes fine today.

I'm begining to wonder if there was more than one factory making these tubes. Like I said earlier, I only found 2 out 48 that tested poorly and even they worked but I wouldn't use them.

Probably just the luck of the draw. Time is also a factor. Just because smoking doesn't kill you in two days doesn't mean that it won't in the long run;)
 

Johnny Z

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Messages
144
Probably just the luck of the draw. Time is also a factor. Just because smoking doesn't kill you in two days doesn't mean that it won't in the long run;)

True time is a factor with all tubes, they wear out. From my experience most amp problems arise from tubes and most new amps that fail can be traced back to a defective tube. Premature tube falure kills lots of amps, after 8 years I'm pretty sure I'm past that point with these tubes and they still test good in the meter. I'm sure there not the higest quality tube out there today but when we got them there wern't many choices available, it was part of the supply left over from my Dad's TV Repair Shop, I must have 2 thousand TV tubes I'll never use.

I don't know why but it seems like I hear of more problems with amps using 6V6's such as Deluxe Reverbs than amps with 6L6's. Quality Control? I don't know. I've had my own problems with 6V6's and I kind of shy away from amps with them any more.

BTW I thought I'ed try a set of Ruby 6L6GCMSTR in my Reverend Hellhound. They seem like a good tube but seem to run a bit hotter than the Westinghouse. Is it because they have larger plates?
 




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