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I took the operating points from the JE Labs EL34 and changed the driver to an EF86. For the driver I went with the triode operating points listed in the Philips datasheet. 350v and 3.15mA current with a 1.2k cathode resistor. I believe the opt would be better if replaced with an EXO-050 but trying to use parts I have on hand. Is the triode strapped driver going to change the value of R1 (0.855 / Plate current) ?
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Not sure where PJ is, but I'll have a crack.Your math for the C4S current set resistor and LED bias resistor are spot on. Dissipation looks to be about 1/2 a watt or so, so no heatsink is required.
The ability of the triode wired EF86 to drive the primary of the RIT5JR is something that needs to be considered carefully! (I would remove it and just use cap coupling) Mikey (and perhaps PJ) will know enough about the RIT5JR to offer more commentary on this matter.
I would guess by the JE labs schemo that the intended design was to use the 125ESE as a 2.5K:8 transformer since the secondary hookup shows the use of the black and white wires. You could nudge the B+ up a little and run slightly less current to better match the TFA-2004 if this is the case.
I seem to also remember bench testing one of these and coming to the conclusion that the cathode resistor value needed to drop a bunch, as we were only getting about 3W out of the amp.
Edits: 07/13/17
I agree with CB. Sorry I didn't post earlier - I wrote a response but apparently failed to hit the "post" button.
He's also right that the EL34 cathode resistor is way too large. The 880-ohm value is not even a standard part, but it was used in the widely-copied WE Model 91 with a 300B. I speculate this circuit was originally for a 300B amp, with the triode-strapped EL-34 swapped in without adjusting for the substantial difference in tubes.
The target operating point is about 350v/70mA for the TFA-2004 impedance of 3000 ohms. I get 360 ohms for the cathode resistor; a 5-watt rating would be marginally acceptable, though I would probably use a 10-watt part myself.
Thanks for the reply Blackplate. I appreciate the suggestion on cap coupling and confirmation on the c4s values. The three watt output would be fine for my speakers, so not really worried about that. I seem to have accumulated a lot of El34's over the years and would like to start using them.
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