PP headphone amp

I've got a pair of 8k ohm PP OPT's with 8-16-32 ohm taps on it and have an idea about using the 32 ohm tap for headphones. EL84's in PP would probably have too much horsepower even in triode operation. Anyone suggest a pentode that can produce less than 1 watt in a PP triode config? I've got a sorts of small TV pentodes like the 12GN7 and such.

I've got a Dynaco ST35 board that may be fun to tweak for this?
 
The amp won't supply any more current than the drivers draw. So your concern is voltage gain, and since the mu of the EL84 isn't any higher than anything else (mu ~20 or so), it is not going to go overly loud. Indeed, a pair of 300B's per side, for example, is not going to be loud at all without a driver as mu is too low. Now, if you push them, they have enough headroom to blow out your eardrums, but that's a different issue.

That said, there are lots of smaller tubes that should work very well. 5687, 6H30, 6n6, 6922, etc. are probably the obvious ones. My own preference would be to skip the Dynaco boards and just use an input transformer. Edcor makes a 10K:10K that will work well for very cheap, or you could upgrade to a Cinemag, Jensen, etc.
 
whitelabrat said:
I've got a pair of 8k ohm PP OPT's with 8-16-32 ohm taps on it and have an idea about using the 32 ohm tap for headphones. EL84's in PP would probably have too much horsepower even in triode operation. Anyone suggest a pentode that can produce less than 1 watt in a PP triode config? I've got a sorts of small TV pentodes like the 12GN7 and such.

I've got a Dynaco ST35 board that may be fun to tweak for this?

Try 6N1P, use 8 Ohm output for 32 Ohm phones. I would try a common cathodes without a shunting cap; one grid for input, another one for feedback from secondary. Just one tube.
 
Actually, I think the ST35 front end driving a pair of video pentodes like the 12GN7 (triode-connected) would work quite well for headphones.

The 12GN7 in triode mode has a mu above 40.

http://www.pmillett.com/pentodes.htm

You could also do a push-pull spud amp, if you have a reasonably low driving impedance to drive the high miller capacitance:

http://www.pmillett.com/el802_spud.htm

Pete
 
pmillett said:
You could also do a push-pull spud amp, if you have a reasonably low driving impedance to drive the high miller capacitance:

http://www.pmillett.com/el802_spud.htm

This is more or less what I was suggesting. But, couldn't you use the input transformer at 2:1 rather than 1:2 to help eliminate the Miller problem. There should still be plenty of gain for phones, and you don't really need that center tap to go to ground, just a couple of resistors.