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In Reply to: RE: JJ KT-77 question posted by dandaroy on March 16, 2014 at 18:45:08
I have used the JJ KT77 and the EH 6CA7 of the tubes you mentioned. I have used the JJ on and off for about 3 years raking up maybe 1000 hours. I have had no problems at all with my quad, they hold their bias very well with little drift and still sound as good or better than when I first got them (from thetubestore.com).
I bought a quad of EH 6CA7 from the same source at the same time and also ran them on an off for about a year (maybe 250 hours) until I had problems with bias drift and noise in two of the tubes so I stopped using them. When they were working they were a good sounding tube, but I always prefered the JJ's. The JJ's are a very alive sounding tube, lots of dynamics and clean detail in the mids, great extention top and bottom. Slightly thin sounding (but not hard) I would usually pair them with warm diver tubes (in my case 6SN7) like the RCA VT-231. The EH 6CA7 has a big, meaty sound to it, but I felt it was harder sounding in my amp.
Lately I have had intrest in trying the EH 6CA7 again so I purchased a pair last month to use with the (almost new) good pair I still have. I was surprised to see that the two pairs are not exactly the same structurally. The (heat) wings on top of the top mica are much larger in the newer pair than the tiny ones on the old pair.
I am wondering if I really have a quad here or if the tubes are different. Have not tried them yet and was wondering how to use them. I could run the different pairs together on each side, run one of each type on each side, or order two more to make a quad (provided they have not changed again). Open to suggestions.
Follow Ups:
I run one of each type on each side when I have mismatched pairs like that.
In one instance, my pairs were actually different 6BQ5's. A GE 6BQ5 with a Sylvania 6BQ5 per side mixes much better than GE x 2 on one side and Sylvania x 2 on the other side.
In the other instance I had two 6L6WXT's with several hundred hours on them and I used them with a brand new pair of 6L6WXT's for a quad .... one of each per side.
Thanks ecline6 for the suggestion. When I get around to it I will try it as you suggest. But its hard to get the EI KT90s out of the amp, they have been in since the end of December and have temporarily cured me of output tube rollingitis.
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