by EWBrown » Thu Jul 24, 2008 2:16 pm
I've posted in the past about using LM317s and 7805s, etc as cathode CCS for the EL84s, it works, but it's best if the tube is running full Class A rather than AB1 or AB2. For an LM317, use 36 ohms for 34 mA or 33 ohms for 39 mA, the idea is to get a 1.25VDC delta between output and adjust pins, the "input" pin goes to the cathode, and teh "adjust (not output) pin goes to ground. Bypass as usual from cathode / input to ground with 100 to 470 uF, 35VDC caps.
For 7805s, use as a simple 5V regulator, input to EL84 cathode, then load teh 5V output with 150-140 ohms, this makes the device regulate at 33.3 or 35.2 mA The exact number fora 7805 and 35 mA is 142.857 ohms, but then we don't have to be "mathematically anal" like Mister Spock, here, within 5% is more than good enough...
The Rev D board has the pads for this, but it isn't (as far as I know) documented in the instructions.
I've modified a "D" board for PP 6S4As, running around 25 mA @ 325VDC B+, but this and all other major projects are on hold until the move to NC is fully completed.
It's raining hard outside and the Gray Tree Frogs are giving me a multi-channel "serenade" Yellow_Light_Colorz_PDT_03 Yellow_Light_Colorz_PDT_04 :o
ed B in NH / NC / NH / NC........
Real Radios Glow in the Dark