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Using unmatched tubes in an MG HEAD MARK III (and my new tubes)

post #1 of 4
11/19/04 at 9:45pm
Thread Starter 
Okay... I've got EL84's that test at 7500, 7550, 7600, and 8000. I want to use the 8000 and 7600 pair for now, and save the other two for later. I am aware 8000 and 7600 are not closely matched. Will this make a difference? Also any difference in using the 8000/7600 pair vs. the 7550/7500 pair? Thanks.

Replacing the stock chinese el84's has definately helped the sound, although the effect is subtle. The new tubes are Mullards branded Rogers that have codes like B7B2, B7C2, B7B3, and I'm not sure what the other one is. It sounds crisper and warmer I think.
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post #2 of 4
11/19/04 at 9:58pm
I doubt it will make an audible difference. I used entirely different power tubes on several occasions without hearing anything that sounded "off"

As long as they are compatible and as long as they work - you should be ok.
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post #3 of 4
11/19/04 at 10:29pm
The two 6BQ5/EL84 output tubes in the MG Head DT and MG Head OTL amplifiers, including the Mark III, do not have to be matched as this is not a push-pull amplifier. Each output tube operates independently as a single-ended triode (transformer mode) or in triode mode when used with the OTL output. The 6BQ5 is a pentode tube, but in the MG Head it is used as a triode. The additional tube grids are not used in this application.

As long as the tubes test in or close to the "good" range on a tube tester, have no internal shorts, and are not microphonic, they will work just fine.

Only twice have I experienced problems with output tubes in the MG Head. Once when I tried a tube that turned out to be highly microphonic. The other time was when I refused to accept that a particular pair of Mullard tubes that showed no signs of life when tested in my tube tester were too far gone to use to power my headphones. They were far too weak even for the limited power requirement of the MG Head. Deadest tubes I've ever seen.
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post #4 of 4
11/22/04 at 5:43pm
gsferrari,

Can you say a bit more about your experiences with changing tubes? I have a Jolida 302B that came with some EL34 Groove Tubes and was thinking about changing them out for some SED's (Winged C's). I was also thinking about changing out the 12AT's and 12XT's as well, but will hold off if the changes are subtle at best. Any thoughts?
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