Well, my pal chis found (runs the service for Beard Audio) had a 211 amp for
years, and just switched to 845, which he prefers. It's not so hard to drive -
these days there are SRPP and mu-follower circuits, good interstages - all
sorts of solutions, even pentode drivers are re-emerging (EL84, C3M etc) Andy.

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

In message , Andy Evans
writes
Well, my pal chis found (runs the service for Beard Audio) had a 211 amp for
years, and just switched to 845, which he prefers. It's not so hard to drive -
these days there are SRPP and mu-follower circuits, good interstages - all
sorts of solutions, even pentode drivers are re-emerging (EL84, C3M etc) Andy.

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

The latest bifilar-wound 1:1 interstage from Sowter would be a good
choice. I've still got my DA100 triodes and the Sowter OPTs I had wound
many years ago, and a rebuild using a good interstage transformer would
be of interest.

The drive requirements of an 845 are near as dammit the same as the
DA100 (once described by Hi-Fi World as 'The Aston Martin of British
power triodes'!).

A 12B4 driver transformer coupled will do the job, but a little B9A 12B4
looks dreadfully weedy against a DA100. (Or an 845)

--
Chris Morriss

Stewart Pinkerton wrote:
On Thu, 28 Oct 2004 18:24:11 +0100, Eiron wrote:


fredbloggs wrote:


bad hair day eh?

In a Lon Chaney Jr. manner of speaking.
It was a full moon last night.


Chuckle. :-)

So, you've met Keith, have you? :-)

By a strange coincidence, The Wolf Man is on BBC2 tonight at 00:40.

--
Eiron.

A 12B4 driver transformer coupled will do the job, but a little B9A 12B4 looks
dreadfully weedy against a DA100. (Or an 845)

A 12b4 has a mu of 6.5 - surely you need more gain than this with a 1:1
interstage? Or are you running it low voltage? Interestingly the low voltage
curves for the 845 look just like the KT66. I have a pile of 12b4 but I have to
say that my favourite input valve these days is a 7913 (2c22). I have quite a
few if you want to try it - it's extremely detailed with very nice high treble.
It's kind of a 6J5G/6P5G but it's even better than those. Andy

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

In message , Andy Evans
writes
A 12B4 driver transformer coupled will do the job, but a little B9A 12B4 looks
dreadfully weedy against a DA100. (Or an 845)

A 12b4 has a mu of 6.5 - surely you need more gain than this with a 1:1
interstage? Or are you running it low voltage? Interestingly the low voltage
curves for the 845 look just like the KT66. I have a pile of 12b4 but I have to
say that my favourite input valve these days is a 7913 (2c22). I have quite a
few if you want to try it - it's extremely detailed with very nice high treble.
It's kind of a 6J5G/6P5G but it's even better than those. Andy

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

There's a cascode-connected E88CC before the 12B4! I don't know any way
of getting enough gain to transformer drive an 845 using only 2 valves.

A 12B4 is low mu (and low Ra of course) which means it has no problem
driving the transformer, and unlike a paralleled-up E182CC it can
tolerate the high voltage swing on the anode.

The SET DA100 amp I knocked up quite a few years ago had 900V on the
anodes of the output valve. I've not tried them at lower voltages but
they should be OK, the big problem is that without driving the grids
positive you can't make use of the whole range of the bottles, so
transformer coupling is almost mandatory. (I guess 845s are the same).
--
Chris Morriss

Andy Evans wrote:
Well, my pal chis found (runs the service for Beard Audio) had a 211 amp for
years, and just switched to 845, which he prefers. It's not so hard to drive -
these days there are SRPP and mu-follower circuits, good interstages - all
sorts of solutions, even pentode drivers are re-emerging (EL84, C3M etc) Andy.


Yes, I wasn't trying to dismiss the 845, just point out that it had its
own set of problems. At the moment I am exploring what can be done with
211's, but I am not able to make the most of them at the moment as I
don;t trust my op TX's above about 800v, so I can;t make good use of the
211 yet. The GM70 in the same circuit was suprisingly good. And if you
can work around he high fillament supply problems, I think it is a good
half way house between the 845 and 211, mu of 8, and works well at about
700v 70ma to give about 15w of single ended output.

I have decided though to concentrate on the 211 first and then look at
what the gm70 can do, currently using a DC coupled 6em7 driver, cloke
loaded and cap coupled to the driver valve.

Final plans involve interstage, I am planning on trying the interstage
that Ae produce, 50H, with a design current of 60ma. And its 98euro for
a pair (double C-Core as well). I will see what the 211 OP TX I am going
to get from them is like and if its ok, the interstage is next

Currently uising 40khz heating from modified lighting transformers..

The GM70 should work with a 211 type TX, but it rearly needs a much
higher current. But in a blind testing at Paul Barkers, the copper plate
GM70 was clearly better, and this is better used at a lower dissapation
that the C plate's 120w.

I thought about the Sowter bifilar TX, but the big problem I can see
with this is being bifaler, it can't be reverse connected, so you can't
take advantage of flux cancilation when grid current flows in A2.

--
Nick

Chris Morriss wrote:

The latest bifilar-wound 1:1 interstage from Sowter would be a good
choice. I've still got my DA100 triodes and the Sowter OPTs I had wound
many years ago, and a rebuild using a good interstage transformer would
be of interest.

The drive requirements of an 845 are near as dammit the same as the
DA100 (once described by Hi-Fi World as 'The Aston Martin of British
power triodes'!).

A 12B4 driver transformer coupled will do the job, but a little B9A 12B4
looks dreadfully weedy against a DA100. (Or an 845)


I am currently very fond of the 6em7 as a gain and driver stage, very
similar to a 6sn7 - 2a3 combination.

--
Nick

In message , Nick Gorham
writes
Andy Evans wrote:
Well, my pal chis found (runs the service for Beard Audio) had a 211 amp for
years, and just switched to 845, which he prefers. It's not so hard
to drive -
these days there are SRPP and mu-follower circuits, good interstages - all
sorts of solutions, even pentode drivers are re-emerging (EL84, C3M
etc) Andy.

Yes, I wasn't trying to dismiss the 845, just point out that it had its
own set of problems. At the moment I am exploring what can be done with
211's, but I am not able to make the most of them at the moment as I
don;t trust my op TX's above about 800v, so I can;t make good use of
the 211 yet. The GM70 in the same circuit was suprisingly good. And if
you can work around he high fillament supply problems, I think it is a
good half way house between the 845 and 211, mu of 8, and works well at
about 700v 70ma to give about 15w of single ended output.

I have decided though to concentrate on the 211 first and then look at
what the gm70 can do, currently using a DC coupled 6em7 driver, cloke
loaded and cap coupled to the driver valve.

Final plans involve interstage, I am planning on trying the interstage
that Ae produce, 50H, with a design current of 60ma. And its 98euro for
a pair (double C-Core as well). I will see what the 211 OP TX I am
going to get from them is like and if its ok, the interstage is next

Currently uising 40khz heating from modified lighting transformers..

The GM70 should work with a 211 type TX, but it rearly needs a much
higher current. But in a blind testing at Paul Barkers, the copper
plate GM70 was clearly better, and this is better used at a lower
dissapation that the C plate's 120w.

I thought about the Sowter bifilar TX, but the big problem I can see
with this is being bifaler, it can't be reverse connected, so you can't
take advantage of flux cancilation when grid current flows in A2.


I hadn't thought about using the grid current to offset the flux
produced by the anode current of the driver! You're right, a bifilar
interstage has to be connected in the correct phase. You can do the old
GEC trick though to extend the HF (and used nowadays in the SEPIC dc-dc
convertor topology) of using a capacitor together with the transformer
to short-circuit the leakage inductance. (Only works if the transformer
is *exactly* 1:1 of course.
--
Chris Morriss

Chris Morriss wrote:


I hadn't thought about using the grid current to offset the flux
produced by the anode current of the driver! You're right, a bifilar
interstage has to be connected in the correct phase. You can do the old
GEC trick though to extend the HF (and used nowadays in the SEPIC dc-dc
convertor topology) of using a capacitor together with the transformer
to short-circuit the leakage inductance. (Only works if the transformer
is *exactly* 1:1 of course.

I have seen that cap trick used with cheap allied interstages as well.

--
Nick

"Keith G" wrote in message ...
(...)

Well, maybe I'll oblige you fairly soon but (believe it or not) one or two
*far* more interesting people than you (offlist) have urged me not to.

Wahey! The lurkers support me in email! It's a classic, practically ancient vinyl.

Steve.