mesherm wrote:If the phase splitter plate resistors are too high in value then the CCS tail can't operate properly. I have used values of 22K in that circuit with a B+ of 250 volts so 16K doesn't seem totally unreasonable.
I had a funny feeling the constant current source had something to do with it, but I have seen CCS circuits before that pretty much used standard value plate resistors. So I was wondering why the change in this circuit.
An LM317 would like to see more current that 4-9 ma so I personally wouldn't use it. I have used 3 terminal regulators as CCS in place of cathode bias resistors before in power stages with excellent results although I use TL783s because of their higher voltage (125v) rating.
You could simplify the circuit even further and combine the phase splitter and output section using a TL783 as a CCS tail for a matched pair of 6L6s. Then use a 12AX7 in SRPP as a VA.
Yes, that is what I originally mentioned when I first started the post, but then the 6U10 came up and at first I thought it would be a far fetched idea as I thought the tube was expensive, BUT the tube is cheap! It is cheaper than a single 12AX7 or 12AU7. So it did get my gears turning to perhaps going with a poseidon 6U10 for a test bench set up.
The compactron pins are the same size as in 9 pin tubes. Its the Lockal tubes that have very small short pins although I have used 7F7s and 7N7s with no problems.
Yes, I read that the Loctals had the problem too. I had trouble finding sockets for them at one time and I sold a bunch of Loctal tubes off many moons ago. I had quite a few 7F7's and 7N7's.
At any rate, on old amps I DO have trouble with 9 pin sockets as well. But I am not concerned with 9 pin tubes as there are 9 pin sockets currently being produced.
The problem I DO have with compactrons is getting them in and out of the socket. One has to be very careful wigging one out. They are tight.
Well, I was worried about the availability of new compactron sockets. (I don't think I would trust NOS sockets). BUT as it turns out, they are making new sockets in China now and that could be enough to sway me to use the 6U10. Again, I might try it out for a bench project. Can't hurt right?
Thanx, Geo
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