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Really quick question: can I run a supply for cathode followers directly-coupled to the power tube grids like this?
Okay, a little more detail if you're interested:
I have a pair of power amps that have bounced around my family a bit. Each of these has a 345-0-345 power transformer that I suspect is good for at least ~250 mA, a separate heater transformer, a 5H 400mA choke, and a 3k2 output transformer with UL taps at ~30% (just going from memory). There are 4 power tube sockets, loaded with EL34s, and three preamp sockets. Oh yeah, and a pair of 2500uF/350V filter caps.
When I got the amps, the PT was bridge rectified through a choke-input filter (using the gigantic choke and caps). Putting upwards of 600V on the plates of EL34s seems like a bad idea. These were used for a stereo, so it's likely they were never pushed very hard.
My plan, then, is to use a more moderate reservoir cap, then use a CLC filter before the plate supply, which will be fed from the gratuitous caps. PSUD2 indicates this will give around +450V loaded (480V unloaded). Since I've already got the bridge rectifier installed, I thought I might as well use a bipolar-looking supply for the bias supply... Then I started wondering about directly coupling into the grids with some cathode followers.
Just to be clear, I won't be pursuing AB2 operation - a sudden increase in current draw would make the B- supply sag quite a bit I'm sure, and looking at the anode characteristics for UL EL34s there's really not much more power to be made. But would it be safe to draw a few mA from this B- supply to feed a pair of cathode followers? Sadly, PSUD2 doesn't simulate this, and I still don't know SPICE.
Thanks!
Okay, a little more detail if you're interested:
I have a pair of power amps that have bounced around my family a bit. Each of these has a 345-0-345 power transformer that I suspect is good for at least ~250 mA, a separate heater transformer, a 5H 400mA choke, and a 3k2 output transformer with UL taps at ~30% (just going from memory). There are 4 power tube sockets, loaded with EL34s, and three preamp sockets. Oh yeah, and a pair of 2500uF/350V filter caps.
When I got the amps, the PT was bridge rectified through a choke-input filter (using the gigantic choke and caps). Putting upwards of 600V on the plates of EL34s seems like a bad idea. These were used for a stereo, so it's likely they were never pushed very hard.
My plan, then, is to use a more moderate reservoir cap, then use a CLC filter before the plate supply, which will be fed from the gratuitous caps. PSUD2 indicates this will give around +450V loaded (480V unloaded). Since I've already got the bridge rectifier installed, I thought I might as well use a bipolar-looking supply for the bias supply... Then I started wondering about directly coupling into the grids with some cathode followers.
Just to be clear, I won't be pursuing AB2 operation - a sudden increase in current draw would make the B- supply sag quite a bit I'm sure, and looking at the anode characteristics for UL EL34s there's really not much more power to be made. But would it be safe to draw a few mA from this B- supply to feed a pair of cathode followers? Sadly, PSUD2 doesn't simulate this, and I still don't know SPICE.
Thanks!