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Old 12th June 2012, 12:13 AM   #1
mbeards is offline mbeards  United States
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Default Best Current Production 6550 / KT88

Hello everyone,

I am new to the larger 42 watt dissipation power tubes and I am working on a P-P hi fi amp that requires 6550s or KT88s

I am wondering if anyone has taken the time to roll any of the current production brands through their system to find the best sounding?

Some people swear by a brand for a particular tube type but I am wondering if anyone has tried many brands before coming to a conclusion.

Im at a loss since I have never tried any 6550s or KT88s before .

Matt
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Old 12th June 2012, 02:29 AM   #2
ChrisA is offline ChrisA  United States
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My opinion. Tubes are not precision devices. I think they are "20% devices" with much variation even between tubes of the same brand.

If you build and amp, typically after you get it to work at all, then you "tune" it by adjusting at least the bias points and maybe the feedback circuit or the value of a grid stopper. Then if you roll tubes it is not fair unless you go to the trouble to re-tune the amp for best performance using the new tube.

Some times people will swap in some brand of tube and claim it sounds "harsh". Then you have to ask them if they changed anything else or not.

Another thing I think is that the brand of audio transformer matters a lot more then the brand of tube? Why don't people "roll" transformers? That is easy to answer because that would be hard to do. So we roll tube only because it is easy? I think so.

I think the best thing to do is best a decent tube. say a "JJ" and then work on the components the surround the tube. If you have a distortion meter it can be a real help. You can turn the bias adjustment pot and watch the THD meter move.
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Old 12th June 2012, 03:11 AM   #3
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Quote:
Originally Posted by mbeards View Post

Some people swear by a brand for a particular tube type but I am wondering if anyone has tried many brands before coming to a conclusion.
Hi Matt;

I tried many brands and found that Gu-50 is better than KT-88. However, you can't swap them, but it is true for new designs.
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Old 12th June 2012, 04:31 AM   #4
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I have just installed PSVANE KT88's in my Tublelab SSE, sound great to my ears, similar to the EH KT88's I was using
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Old 12th June 2012, 04:36 AM   #5
mbeards is offline mbeards  United States
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Agree completely with tubes being a non precise beast. Good tip on the THD meter. Once it is all buttoned up I plan to do some thorough scholarly testing on lots of parameters to see how well it turned out.

As for transformers, I am using some very very beefy custom wound electra print's.

the GU-50 is a russian tube correct?
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Old 12th June 2012, 04:40 AM   #6
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Give Chris a "cigar". Each type and manufacturer of said tube requires designing around that tube. I have found that to be the case as well for small signal tubes as well.

Simply plugging in different tubes into the same circuit will not necessarily give an honest answer as to which is the best.

Cheers.
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Old 12th June 2012, 04:45 AM   #7
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Quote:
Originally Posted by mbeards View Post
the GU-50 is a russian tube correct?
Correct. It is Russian military tube. And unlike KT-88 it is greatly under-priced, while tolerates greater abuse.
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