Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tubenit on June 19, 2010, 06:49:31 pm
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I had a pair of original Tung-Sol 5881's that HotBluePlates gave me. One finally went very microphonic after several years of use.
I bought a new pair of JJ 6L6's and after about 10 hrs ...... one went white when the glass made a perfect circle break in the middle. What's that about?! I seem to have awful luck with any JJ's except the 6V6's. I've had a 12AX7, EL84 and 6L6 all go bad.
:undecided:
So I have one JJ 6L6 and one original Tung-sol 5881. Thinking about pairing them up in the same amp. How many ma's of current do they need to have to be reasonably OK? I have a Hoffman bias checker I built so I find out the individual ma's.
I sort of thinking ........ if they sound good and one of them doesn't redplate from pulling too much current then use them as a pair?
It's for my T-Lite 5879 OD which is cathode biased.
With respect, Tubenit
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5mA difference is quite acceptable. Some would say keep em within 10%. It's really not as important with guitar amps as it is with hifi as long as they're not seriously different. I've had bad luck with JJ's too. More recently, 1 of 6 - 6L6GC (Ruby) was bad out of the box. 5 read 32mA and the 6th one was 58mA and slightly red plating. I did the tube socket shuffle and the problem followed the tube. When tube glass goes white, it means the bottle sprung a leak. I haven't had that problem with JJ's. All of my troubles have been centered around octal tube pins being smaller which left me with the choice of replacing the sockets or going with a different brand of tube. New tubes take 2 it was.
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My JJ EL84s developed a rattle almost right away at volume. The ancient Harmony and brand new Sovteks have no issues in the combo amp. (so far) And come to think of it, the rectifier tube that cracked was a JJ as well.
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I had a pair of original Tung-Sol 5881's that HotBluePlates gave me. One finally went very microphonic after several years of use.
I bought a new pair of JJ 6L6's and after about 10 hrs ...... one went white when the glass made a perfect circle break in the middle.
Well, that sucks! I think I still have a few more TS 5881's. When I get back in town, I'll check and give ya another one. I'd probably be interested in checking out the microphonic one and seeing what's going on with it. With that construction style, they definitely shouldn't get microphonic. I'll probably try to find a way to use it, even if it winds up being as a series regulator in a power supply.
So I have one JJ 6L6 and one original Tung-sol 5881. Thinking about pairing them up in the same amp. How many ma's of current do they need to have to be reasonably OK?
I agree with what you were thinking. 30mA difference is probably too much, and you'd hear it as either hum in the output or reduced bass from saturating the OT. 10-15mA apart... I'd personally use them.
I know matched tubes are the "holy grail" or whatever, but the biggest issue for us is OT saturation. The next big issue (that most matching probably doesn't even address) is that if the dynamic characteristics of the tubes aren't matched, you won't get maximum clean output power. But we like distortion from the output tubes, right?
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Thanks for the answers, guys. I pop those in, measure them and hopefully use that mismatch.
HBP, I got lots of use with that tube set. I've had them in regular use since you gave them to me. I liked them better
than the Tung-Sol re-issues.
Looking forward to your return home!
Best regards, Tubenit
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Yeah, I'd give it a shot. Keep an eye on the plates, but if it sounds good, it is good.
Back in the old days, we'd run any combo of tubes we could get our hands on (whatever the corner store sold), didn't worry about matching (as long as the tube-type matched) & the amps sounded great!
$.02
Geezer
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Set up the bias controls to bias each tube separatly. Then use any tube you want... It's way cool.
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It's for my T-Lite 5879 OD which is cathode biased.
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I'm losing it. Sorry!
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Thanks to Hoffman's bias checker, I was able to check the current pull on these tubes. The original Tung-sol 5881 was running at 52ma compared to 32ma of the JJ 6L6's. I am not going to use them with that far apart. The weren't red plating after 10 min of playing but the tung-Sol 5881 was running very hot compared to the JJ.
With respect, Tubenit