Quote:
Originally Posted by majoco
EL84's do run pretty warm, but it's strange that the pair are different temperatures especially as the one out in the clearer air is the one getting hot. Is it a push-pull output stage or bi-amped with one amp for each bass speaker. Check the value of the cathode resistor, the cooler running one may have gone high which will cause your distortion maybe....and yes, EL84's can and do suffer from grid emission when they get old - measure the voltage across the cathode resistors - they should be about equal and a reasonable value, say 6 volts or so IMHO.
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Its push pull as far as I know, especially since its mono only output.
Right now everything is out of the chassis, so there is plenty of airflow. I can feel the heat rising from the top of the EL84's, but one of them is certainly hotter. I cannot touch it with my fingers - its about as hot as a 40w light bulb i'd estimate. I'll check the resistors tomorrow.
As an update, I replaced about 10 more caps this evening. At this point pretty much all of the high voltage paper caps that were leaking/melted are replaced. I tested after each replacement, unfortunately I didn't hear too big a difference after replacing one.
The last one I did for the night was disconnecting the 50/50uf can at the top, and putting new ones on the underside. After turning it back on (and hoping they wouldn't explode
) I was greeted to a HUGE improvement in sound. Almost all the distortion is gone at this point, and the volume and clarity are much improved. The amount of bass this guy puts out is amazing! There is still a little bit of "looseness" to the sound, especially in the lower frequencies, but I hope that the remaining caps will fix that.
There is still one electrolytic left to replace - a 2uf unit. I ordered one online since I couldn't find it locally, however what came was a 2uf unit, but not an electrolytic. The voltages exceed the original, but i'm not sure if I can replace an electrolytic with a non-electrolytic. Would this be ok?