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Guys, I blew up my Kay 720. It's my own damn fault too, I was playing it one night and when I finished up, I got distracted somehow. I went upstairs and left the damn thing on. I'm a dumbass.
When I went back down there a few days later I realized what I had done when I saw the fuse was blown. When I replaced the fuse it wouldn't power up, it popped the fuse as soon as I hit the power switch. Something had fried during all that time; don't know how long it ran before failing.
I pulled the power tubes and it still blew the fuse. I pulled the rectifier tube and it still blew the fuse.
I took it apart and there were no obvious issues. Nothing burnt or cooked. I checked the screen resistors and they were good. I checked the 50r, 47k, and 22k around the filter caps and they were good. The 180k resisters were good.
I checked the speaker and it is good.
The filter caps are original. I know, I know, but when I refurbished this thing I was getting no hum and it sounded fine, so I thought I would wait. Dumb.
I looked at R.G's tube amp debugging pages and did some checks on the filter caps but I'm not sure about the results. The .47 read open. I will replace them but I sure would like to know if that is the issue rather than blindly changing parts. I can get a cap can from Antique electronics, I can't find a .47uf but Mouser has a 450v 1uf with the proper voltage rating, I guess that will work?
I didn't disconnect anything for the checks, I'm not sure if that was necessary or not. The cathode resistor on the power tubes measured 25 instead of 250R, but the 25uf cap was on it and I don't know if that throws the reading off.
R.G. has instructions for checking the transformers but I admit it was a bit bewildering. Maybe a little simpler explanation there would help me.
I'm really not very good at problem determination, pretty bad in fact. If you guys would give me a few pointers before I give up and take it to my amp tech Jeff I'd appreciate it. I love this amp and want to get it working again.
I've attached the schematic. The stuff in red are my mods.
Thanks,
Regis
When I went back down there a few days later I realized what I had done when I saw the fuse was blown. When I replaced the fuse it wouldn't power up, it popped the fuse as soon as I hit the power switch. Something had fried during all that time; don't know how long it ran before failing.
I pulled the power tubes and it still blew the fuse. I pulled the rectifier tube and it still blew the fuse.
I took it apart and there were no obvious issues. Nothing burnt or cooked. I checked the screen resistors and they were good. I checked the 50r, 47k, and 22k around the filter caps and they were good. The 180k resisters were good.
I checked the speaker and it is good.
The filter caps are original. I know, I know, but when I refurbished this thing I was getting no hum and it sounded fine, so I thought I would wait. Dumb.
I looked at R.G's tube amp debugging pages and did some checks on the filter caps but I'm not sure about the results. The .47 read open. I will replace them but I sure would like to know if that is the issue rather than blindly changing parts. I can get a cap can from Antique electronics, I can't find a .47uf but Mouser has a 450v 1uf with the proper voltage rating, I guess that will work?
I didn't disconnect anything for the checks, I'm not sure if that was necessary or not. The cathode resistor on the power tubes measured 25 instead of 250R, but the 25uf cap was on it and I don't know if that throws the reading off.
R.G. has instructions for checking the transformers but I admit it was a bit bewildering. Maybe a little simpler explanation there would help me.
I'm really not very good at problem determination, pretty bad in fact. If you guys would give me a few pointers before I give up and take it to my amp tech Jeff I'd appreciate it. I love this amp and want to get it working again.
I've attached the schematic. The stuff in red are my mods.
Thanks,
Regis
Attached Files
Not to be unsympathetic to the situation... But I'm new to this stuff, and need to be led by the hand.
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