13-05-2020, 04:50 PM
Mark Hennessy Wrote:But the trouble with a distorting valve amp is that you can't bypass the distortion.
Why not? I'm thinking (consider something like the Mullard 3-3 which has been mentioned in this thread), a 2-position switch. One position is as-Mullard; the other position removes the negative feedback, and also introduces an input attenuator to bring sensitivity down to the with-feedback level.
Distortion isn't bypassed, it's cancelled - but you get the same thing.
Mike Watterson Wrote:I "repaired" one modern valve amp that had an EL84 and a similar Octal valve (forget which KTxx Beam Tetrode) and what looked like a too small audio transformer. An EL84 is described as Pentode, but actually it also is a beam tetrode. The g3 isn't a grid like on an EF80, it's beam forming plates.
I doubt that - so I had a look in an EL84 (luckily to hand right now!) and doubt it even more.
The g3 support rods can be seen through a couple of apertures in the anode, and there definitely is a spiral grid wound on them.
Mullard / Philips denied the beam tetrode (Not Invented Here) and did describe a few of their valves as pentodes for marketing purposes, eg DL92 which definitely is a BT. But not the EL84.
