zippy1540 wrote:trying to decide on my next amp. the -35 sounds awesome with the el84m's but looking for more power. anyone tried PPP EL84'swith the poseidon or st35 driver???
Tube Amp Newbie
Yellow_Light_Colorz_PDT_09
I've done it with an ST70 driver.
Here's what I learned:
1. Keep the B+ reasonable. It IS possible to run EL84 PPP ultralinear
at 425V, if you handpick the tubes... using a B+ of 350 or less
will avoid a lot of potential problems.
(BTW, you can get 50W out of PPP EL84 at 425V Yellow_Light_Colorz_PDT_09
2. Keep the grid circuit resistance down. The DIYtube ST35 has
470K, which is way too much. You really want 150K or less,
the DIYtube ST70 board has that stock, the Poseidon 100K.
3. You may have to experiment with screen resistors and/or
small pf caps betwixt plate & screen to avoid oscillation,
keeping the B+ reasonable reduces the likelyhood of that
kind of problem. So does using cathode bias, although that
cuts your output power down a bit.