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- Jan 24, 2009
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Those are Cossors, probably the best match for this amp in its stock form. Based on my measurements if you pick up a good pair of Cossors they will last you a long time.
I've been comparing Cossors to TT21 without top cover and it seems like the amp is not designed to run higher power tubes despite manual saying KT88 and 6650 are ok. Things heat up noticeably more, including the core of the power transformer. The hot spots are the two power mosfets driving output tubes. I think I'll take my amp further apart to see if I can do something about those two mosfets- maybe even move them off the board to give them better thermals. The mosfet for the left tube is actually worse off than the right one because it is tucked into the board and airflow is more restricted there. I can't imagine what temperatures will be inside if I close the case. Mosfets might be able to take it for some time, but it won't be good for the rest of the circuitry including caps. Elekit did too good a job packing this thing into a small case. If they made it more loose it would have been better for upgradability and passive cooling. Another alternative would have been a case with aluminum fins but the kit would cost much more if they went that way.
I've been really digging them so far and I got them new, tested twice, so happy.
Very interesting observations, I too was concerned about both heat buildup as well as airflow within the kit myself. Since doing the mods, the outside case is much cooler, but I've always wanted to throw some temperature probes down the modded air vent and test the temps running in both normal use and then trying to heat it up. Unfortunately since I already cut into the steel, I can't really test it without the mod and then compare. Stock would even be a bit challenging, since you would have to get the probes into the closed case somehow anyway, probably having to use either existing screw holes or by drilling; would have to look into options. However, with the mod I did linked back here, even the airflow grate I'm using gets warmer to the touch than the surrounding area, so I think some airflow can really help, especially in the long-run as over time the excessive heat can/will degrade certain components.
I'd be interested in what else you are able to find out.