Around ten years ago I built a Cornet Octal phono preamp employing point to point wiring as well as a CCS on the cathode follower. I was happy with the outcome and it sounds very good...but it seemed to run the 6SN7 a little hot. It's on the bench again so that I can try some different first stage and output capacitors, and I figure I'd have another look at it.
Full schematic here: https://www.hagtech.com/pdf/cornetoctal.pdf
As It turns out, the CCS circuit I was using ran the plates at 11mA for a dissipation of slightly over 3W per side. A little more power than I was comfortable with considering the new production T-S 6SN7GTB I have installed is rated for only 2.5W. The original CCS was arranged as follows:
As depicted below, I modified the circuit to reflect changes implemented in the Cornet V3 while also increasing R21 to 820R to reduce Ip to 6.7mA, which lowers plate dissipation to 2W. With concern to the tube's longevity, should I drop it further (perhaps through a reduction in anode voltage)?
I'm having some trouble understanding the purpose of the series LED in the revised circuit. Normally I see LEDs used for biasing, and I'm wondering if I should employ such an arrangement for this circuit.
Thanks for any input.
Full schematic here: https://www.hagtech.com/pdf/cornetoctal.pdf
As It turns out, the CCS circuit I was using ran the plates at 11mA for a dissipation of slightly over 3W per side. A little more power than I was comfortable with considering the new production T-S 6SN7GTB I have installed is rated for only 2.5W. The original CCS was arranged as follows:
As depicted below, I modified the circuit to reflect changes implemented in the Cornet V3 while also increasing R21 to 820R to reduce Ip to 6.7mA, which lowers plate dissipation to 2W. With concern to the tube's longevity, should I drop it further (perhaps through a reduction in anode voltage)?
I'm having some trouble understanding the purpose of the series LED in the revised circuit. Normally I see LEDs used for biasing, and I'm wondering if I should employ such an arrangement for this circuit.
Thanks for any input.
Not a bad idea, although I've never had problems with arcing using a 6087 which is indirectly heated.
I couldn't find anything referencing stated degradation, but I added a couple of 1n4005s directly between the grids and cathodes since I had them in stock.