On Aug 7, 10:11 am, Nick Gorham wrote:
Hi,

Given its been a bit quiet on here, I thought I would post some of DIY
output.

Here is a link to some pictures of the GM70 amp that I have been working
on for the past eight months.

http://www.lurcher.org/nick/images/gm70/

Circuit is a C3g Pentode voltage amplifier with VR tube screen
regulator, then 300b driver to 1:1 amorphous interstage to GM70 grid.
Output TX 7k amorphous. Driver and 300b supply, series regulator using
6080, ecl82 and 0d3 (Steve Bench inspired). TJ-Meshplate 300b, running
330v @ 55ma. Copper plate GM70 running 1020v @ 110ma.

All transformers by Automatic Electric Europe.

Rough specs, -3dB points (5w into 8ohm) 18Hz, 52kHz. 3% distortion
reached at 42w into 8 ohm.

It was designed to drive a set of large panel electrostatics, but I have
been using the breadboard version driving a pair of Yamaha NS1000's. My
normal 94dB/W speakers are slightly overpowered for them :-).

I can't take too much pride in them, as their owner did the construction
and I did the design and internal build. But I am still very pleased how
they have come out.

--
Nick

Very nice indeed, Nick. We'll have to drum you out of the club for all
those heresies -- pentodes indeed! series regulators, gee! -- but I'm
sure your amp sounds brilliant precisely because of them.

Andre "Real Men Shunt" Jute (1)
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

....regulate, that is. To join the ultrafidelista, next to every tube
shove up a bigger power tube to shunt its current. For those who were
educated too long ago to remember shunt regulation, and who haven't
"read" anything except Playboy since, shunt regulation consumes half
the power, so the shunt tube must be capable of handling twice the
desired operating current.