Howdy folks!
A couple weeks back I was having some issues with the coupling caps used in my PS to develop my bias supply.
Many thanks to all the members who so graciously helped me out!
I replaced the Sprague Orange Drops (600VDC/300VAC rating) which were in series with the 400VAC HV secondary and eventually shorting-causing my bias voltage to plummet and my plate voltage to soar-with some Cornell Dublier 3000VDC/1000VAC poly caps.
After an hour, the caps are just barely warm to the touch, bias is rock solid. Schematic lists 475v on the plates of the 7591s at 33ma per tube, or .9v drop on the four cathode resistors to ground at the DC balance test points.
Now, at 33ma per tube, I'm at 474v on the plates-I'd say that's close enough, and the amp is finally working correctly for the very first time!
The sound is first-rate and I can't keep myself from continually checking DC and AC balance because I get such satisfaction out of getting the same exact reading over and over!
Thanks again for the help folks-this site and its' members ROCK!!!
Best,
mr mojo
A couple weeks back I was having some issues with the coupling caps used in my PS to develop my bias supply.
Many thanks to all the members who so graciously helped me out!
I replaced the Sprague Orange Drops (600VDC/300VAC rating) which were in series with the 400VAC HV secondary and eventually shorting-causing my bias voltage to plummet and my plate voltage to soar-with some Cornell Dublier 3000VDC/1000VAC poly caps.
After an hour, the caps are just barely warm to the touch, bias is rock solid. Schematic lists 475v on the plates of the 7591s at 33ma per tube, or .9v drop on the four cathode resistors to ground at the DC balance test points.
Now, at 33ma per tube, I'm at 474v on the plates-I'd say that's close enough, and the amp is finally working correctly for the very first time!
The sound is first-rate and I can't keep myself from continually checking DC and AC balance because I get such satisfaction out of getting the same exact reading over and over!
Thanks again for the help folks-this site and its' members ROCK!!!
Best,
mr mojo
Congrats 🙂 But you forgot the pics 😀
I have half a dozen 7591s that will eventually become my guitar amp 🙂
I have half a dozen 7591s that will eventually become my guitar amp 🙂
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