simple EL84 parallel?

[harley]

Anyone tried extending the power output of the simple EL84 with CCS by paralleling the output valves (2 to 4 or more)?

Also, I've not seen clear documentation of what the output power of this amp is. I think it is about 10W, is that right?

[vinylkid58]

Originally Posted by harley

I think it is about 10W, is that right?

Cathode bias pentode should get to 12W. Tubelab?

jeff

[aardvarkash10]

in practise, probably less in the simple (self splitting output) design. 8 to 10-ish watts.

[harley]

so no attempts I take it?

[ArtG]

With Dave Gillespie's EFB bias mod, a Dynaco ST35 (EL84 PP, UL) will produce 17.2 watts per channel from 20Hz to 20KHz both channels driven) at a maximum of 1.7% distortion at 20Hz (much lower at higher frequencies).
A recent post on this forum "Doubling the power of hifi tube amplifiers" shows the impressive result of doubling the output tubes of an Eico amplifier that utilizes 7591 outputs.
The techniques discussed in this article could be, and should be applicable to an EL84 amplifier, although I don't believe that anyone has yet tried it.
If you are willing to experiment with this technique, there could be some worthwhile gains possible.

[harley]

what about using an LM317 CCS for each tube? Would that not be better than the EFB bias mod?

[rmyauck]

Dave Gillespie mentions that LM317 CCS doesn't work well in his articles. Check diytube for lot's of info. Extra tubes should double power, but you would have to change resistor value for cathode bias, plus use a output transformer with half the primary impedance. EFB mod should work too and give all the benefits. You can then keep the dissipation below 12W for use of many different tubes and long life if you set them at 27 mA ea.