I am repairing an 805 SET amp, driven by a DC 300B, and this is the second time the bias winding for the 300B has gone open in this amp and I'm wondering what could be causing it. It was replaced once by the previous owner, and now it's my turn. It's a dual mono chassis with very robust transformers, very well made JAS 2.1 amp. It's a very simple circuit, I have checked the bridge and zener, both fine, and also ran the bias winding from the good channel to the input of the bridge just to check and it works fine.
So my question is, how much grid current, if any, is drawn by a 300B cathode follower directly coupled to an 805. I'll attach schematics so you can see what is going on.
I have 2 options, I could use the good channels' bias winding for the grid supply for channel 1, or install a dedicated bias supply xfmr for the bad channel, maybe get it big enough to handle both channels if the good one fails some day.
Thanks!
So my question is, how much grid current, if any, is drawn by a 300B cathode follower directly coupled to an 805. I'll attach schematics so you can see what is going on.
I have 2 options, I could use the good channels' bias winding for the grid supply for channel 1, or install a dedicated bias supply xfmr for the bad channel, maybe get it big enough to handle both channels if the good one fails some day.
Thanks!
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