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I'm planning a PP amp using a EL12N(precurser of the EL34). The datasheet says it has a S of 15ma/V.

15 mA/V equates to 15,000 umhos (micro-mhos). EL84 /6CA7 is 11 ma/V (11,000 umhos).

http://frank.pocnet.net/sheets/082/e/EL12N.pdf

HTH

/ed B

So it needs even less drive than a EL84?

Not really.

In a tube circuit that doesn't draw grid current (A, AB1), the amount of drive you need will be twice the bias voltage for the tube. An EL34 in a typical circuit for that tube will have about -32V of bias, requiring at least 64V of clean swing (you want headroom for the driver, so make sure it can do 80V or so, then run it at a lesser driven value). An EL84 requires about -12V, therefore 24V of clean swing.

Cheers!

Looks like this tube would require a -/+ 19V grid drive in Class AB1, PP operation, with an 8K A-A OPT.

http://frank.pocnet.net/sheets/082/e/EL12N.pdf

It would be good idea to have some additional drive capability, in order to properly (cleanly) handle any brief peaks or transients.

It looks like they are using cathode bias (350 ohms per EL12N), fixed bias would be even better for power output and lower THD

For Class A Pentode single ended, VA = 250V, IA = 72 mA, I G2 = 11 mA, 3.5K OPT, RK = 90 ohms, R G1 = 30K, it would require +/- 7V rms drive.

/ed B

Transconductance-wise (EL-34=12, EL-84=11, KT88=12, EL-12N=15) are about in the same ball-park. Unlike the EL-34, the EL-12N is only an 18 watt tube, and it has a much lower max voltage rating - according to some spec sheets.

http://tdsl.duncanamps.com/show.php?des=EL12N

It's close to the 6L6 in max PD, so you could use 6L6 amps as guides for plate voltage and bias current. For an AB1, PP amp, 425V is a bit too high. 350V seems the ticket.

350V * .0425A = 14.875W

I got the EL12s from askjanfirst.com I wanted some real German tubes (even though I already have a bunch in radios). I had never heard of the EL12 and luckily Jan has them for 8 euros each, although not necessarily EL12Ns, they look like EL12Ns, but they say EL12/375. I also got 2 EF6s, 2 ECH4s ,and 4 EBC3s. The ECH4 is an interesting tube, it was designed as a frequency changer that can be used as a audio amp and phase shifter. I'm planning on using it as an LTP.
http://www.mif.pg.gda.pl/homepages/fran ... e/ECH4.gif

I guess I can use the EF6 up front, as either a pentode or triode. And then the EL12s in back. The challenge is only the EL12s have curves. As for the rest of them, it makes it easier if they don't have to swing a big signal, to keep things more linear.

I'd like to advice You use EBC3 - section C in prestage. EF6 use in triode mode for phase splitter.

I put the EF6 in front and the EBC3 as phase splitter, I wanted to make sure I had enough gain. With the EF6 as a pentode, with 6db feedback I'm getting about 40 times gain. Which seems to be just enough. With a little over 1vpp in I can drive it to clipping at about 7/8 of the way up with 28 watts. I'm using Edcor's 25 watt transformers in UL. I've built one side, now I'm building the other. Had to stop and repaint the tubes.