14 Aug
2014
14 Aug
'14
2:57 p.m.
On Aug 14, 2014, at 16:33, William Donzelli <wdonzelli at gmail.com> wrote:
The expense and weight of the output transformer is not at issue with current OTL (Output
Transformer-Less) designs, but rather distortions introduced by the output transformer
through core loss, hysteresis, etc. I've seen modern designs that use a pile of
hard-to-find Russian military tubes to achieve an output impedance of about 2.5 ohms.
It all sounds like an expensive exercise in masochism to me, but then the only thing I
want from a tube amp is volume and distortion when I'm playing my guitar through it.
OTL topologies don't really come into play there.
Lots of interesting modern tune design principles at http://www.tubecad.com, though,
including some very nice high-PSRR designs.
- Dave
I remember
seeing some circuits using paralleled triodes in a
cathode-follower configuration being touted as transformerless speaker
drivers. I don't know if they ever made any headway in the commercial world
as such.
I doubt so, back in times past, because audio output transformers were
relatively cheap, and the big low-mu monster triodes were not. Now
things have changed, and 6AS7 and friends often can be purchased for
peanuts, so there are indeed tube amplifiers that lack output
transformers. One must be very careful with them, and use proper
speakers, or there will be trouble.