low voltage single ended el84

[Helmholtz]

3. Adjust the cathode bias resistor to get 65mA or so cathode current. That's less than 80% max dissipation considering screen current, so you can safely go higher (or lower) than 65mA.

Don't forget that the max. (average) cathode current for a real (PH, Valvo, Mullard, TFK) EL84 is 65 mA.

[cminor9]

Alright! I will report back when I get something. Gonna build this with a friend who is interested in learning, so that’ll be fun too.

Much appreciation for all of the advice!

[Gingertube]

The Application Report has details of B+ of 200V operation - that will do.

Cheers,
Ian

[tubeswell]

I
So I read this: https://robrobinette.com/Drawing_Tube_Load_Lines.htm and this: https://wtfamps.com/load-line-calculations/ Those seem to fill in some gaps for me.

(Warning - Rob drew a 4k load line for one 6V6 tube and has it idling at 10.88W, and the load line crosses Pmax curve.)

For PP load line lessons - see http://www.valvewizard.co.uk/se.html then, http://www.valvewizard.co.uk/pp.html (each Class A load line is drawn as per a single-ended load line, and then you flip it around and invert it.)

To draw the grid curves at the desired screen voltage you want, you can use a transfer characteristics chart to eyeball the height of the grid curves on the plate characteristics chart. (The JJEL84 datasheet has these two charts conveniently plotted side-by-side for doing this). The dotted red lines in the attached chart project some eyeballed g1 voltages onto the plate characteristics chart and the point where these intersect the plate voltage abscissa (green dotted line), is the horizontal reference point for each grid curve (which you copy the shape of from the existing grid curves, and smudge things a bit - its all ballpark stuff after all)

[Chuck H]

Also... If you go with a universal primary OT this point is moot, but if you go with a fixed ratio OT you can always adjust the speaker impedance to half the reflected ratio/primary impedance. If you used an OT for an 8 ohm secondary you could use a 4 ohm speaker like you normally would for a Champ and there are plenty of good sounding models available. This does have the down side of reducing the relative inductance and raising the LF knee, which is already pretty poor with most readily bought, fixed ratio Champ-ish OT's. If you just want the right OT for the job rather than a universal primary type, on my last single ended build I went with the Edcor XSE line and was very happy. They are 10W units. The price was good, but it cost as much as any other anyway because of their stupid, high shipping charges. Their GSXE line offers some 5W units if that aesthetic appeals to you.

https://www.edcorusa.com/xseseries
https://www.edcorusa.com/gxseseries

EDIT: P.S. Nice to see you and welcome back