08-26-2011, 12:36 PM
I am working on a JR-20. I am not sure what I intend to use it for yet, but I want to get it working. I was messing primarily with tubes last night, and haven't gotten to check any voltages yet. I just thought I'd post some observations and maybe someone will notice something familiar. I started by removing the power tubes, while powered up, the bass channel is never very loud and at 200hz crossover, there isn't much definition there anyway. My most obvious find is that, with the treble channel especially, if I put a pair of power tubes in it, I get some volume, but it distorts pretty easily. If I pull one power tube of the pair for the treble channel, it gets louder and clearer. Like I said, I haven't checked any voltages yet, but my limited tube experience suggests that maybe my power supply isn't keeping up and I don't have enough voltage when I put in the other tube. One thought I have that I didn't think to try last night, if it is the power supply, I should see the same effect if I have it running on one tube on the treble side and put one in the bass side (I was doing my experiment with the bass channel power tubes removed), that should pull down the power supply the same as adding one to the treble channel, correct? I realize I can figure this out by simply repeating this experiment measuring the voltage, but I won't be home til this evening. The power transformer in this amp was left on for a week, the rectifier tube was bad and the power transformer got VERY hot, some of the potting ran out the bottom of it, the power transformer in the AO-10 in the organ (left on at the same time) was burned up (literally, almost started on fire). I have to say, running a single 6V6 on the treble side it sounds pretty clean and is reasonably loud. Anyway, just starting the process of getting this thing up to speed.