I was reading about this circuit and wondered if anyone had built one or had
views about the high claims of efficiency and damping factor and low distortion
made.

http://www.plitron.com/PDF/PB/Article/Atcl_4.pdf


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

Andy Evans wrote:

I was reading about this circuit and wondered if anyone had built one or had
views about the high claims of efficiency and damping factor and low distortion
made.

http://www.plitron.com/PDF/PB/Article/Atcl_4.pdf

Super triode is the name given to the ciruit which is really UL
with CFB.
I used it for some years with Ea = Eg2 = 375V, before realising that plain CFB with
a regulated EG2 at 400v, Ea = 480v , gave lower thd, more power and sounded great.
I like to have the CFB between 15% and 20% of the total primary turns.
I use a quad of 6550, and get 50 watts nearly all class A into 8, and 85 watts AB
into 4,
about 95 w into 3.

Patrick Turner.



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

yes Andy. I think van der Veen should be read with some caution
though. He was and possibly is retained by Plitron. He tends to talk
up the good features, and his research is largely rehashed from
history. "Super Pentode" has been used elsewhere, and the
configurations themselves were not new.

My amps use transformers made for me by Sowter, who did an excellent
job. I seem to associate you with 4 * EL84 and a direct-coupled
input/concertina combo? Mine are 5k into 6ohms with 30% UL and 10%
CF, which would be about right, although I use 6CH6 beam tetrodes.

With no overall nfb I drive a pair of not-very-easy bookshelf
speakers with no problem. Output resistance is about 0.5 ohm as far
as I know. In class A very little distortion is generated by the
output stage, so the total is dominated by the 2H of the first
valve. Sounds good to me. I can double the power by reversing the
screen connections, but I don't feel in a position to recommend this
until I have run it for a few months with the ensuing extra peak
screen current. It increases output resistance too.

I think the configuration is better with beam tetrodes. One
important feature is that screen current passes through the CF
winding, and I think this plays out better than with pentodes. Could
be wrong, haven't measured it. One of the reasons it would be nice
to talk to Russ Sadd again. Or Denis. (come back Denis)

A couple of factors you should be careful to take into account.
First, the extra voltage drive required, which increases the (mostly
2H) from the input valve, and the (mostly 3H) from the concertina or
whatever. If you don't want to use overall nfb, you might consider a
mu stage or whatever for the input.

I use high gain output valves, which helped with that. The second
practical problem I still haven't sorted to my satisfaction is the
limits imposed by grid and screen current at low voltages. I can't
run them as deep into class A as I originally intended. The low Vak
results from driving the cathodes up at the same time the anodes are
coming down.

I reckon the 6550 family is probably the best bet, amongst common
valves. I would like to hear from anyone using 12E1 or 13E1 in this
way.

The ideal would be a high gain beam tetrode with a steep rise up to
a sharp knee at low current.

One more thing I have noticed. Most of the people who pursue the
configuration seem to gravitate towards the Quad 2. Van der veen, I
remember, was into paraphase mu-followers (as opt to paraphase
pentodes used in the Quad).

cheers, Ian

"Andy Evans" wrote in message
...
I was reading about this circuit and wondered if anyone had built
one or had
views about the high claims of efficiency and damping factor and
low distortion
made.

http://www.plitron.com/PDF/PB/Article/Atcl_4.pdf


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