[Fai C]

My friend don't know English, and that's why I wrote for him and he
bought a pair of Plitron output transformer for 211 many years ago .

See link for details: http://shop.plitron.com/specs/414900.pdf

Regardless of the driver section, can he have the 211 for the
Criclotron output stage with this output transformer from Plitron?

Thanksl!

[John L Stewart]

Originally Posted by Fai C

My friend don't know English, and that's why I wrote for him and he
bought a pair of Plitron output transformer for 211 many years ago .

See link for details: http://shop.plitron.com/specs/414900.pdf

Regardless of the driver section, can he have the 211 for the
Criclotron output stage with this output transformer from Plitron?

Thanksl!

The short answer is probably not. The OPT could be used but will not give optimum results. Plate loading for the Circlotron type OP is 1/4 that used in ordinary PP operation. If the OPT was originally intended for PP 211s, the loading will be 4X required. Resulting power will be less than 1/2.

email me direct for a full article on a practical Circlotron type ampliufier I authored for publication about 10 years ago. Lots of test results included.
Uses KT88, 6550s & other combos.

jh dot stewart at sympatico dot ca

Cheers, John

Cheers, John

[Patrick Turner]

On Dec 11, 10:07*am, John L Stewart John.L.Stewart.
wrote:
Fai C;945928 Wrote:

My friend don't know English, and that's why I wrote for him and he
bought a pair of Plitron output transformer for 211 many years ago .

See link for details:http://shop.plitron.com/specs/414900.pdf

Regardless of the driver section, can he have the 211 for the
Criclotron output stage with this output transformer from Plitron?

Thanksl!

The short answer is probably not. The OPT could be used but will not
give optimum results. Plate loading for the Circlotron type OP is 1/4
that used in ordinary PP operation. If the OPT was originally intended
for PP 211s, the loading will be 4X required. Resulting power will be
less than 1/2.

email me direct for a full article on a practical Circlotron type
ampliufier I authored for publication about 10 years ago. Lots of test
results included.
Uses KT88, 6550s & other combos.

jh dot stewart at sympatico dot ca

Cheers, John

Cheers, John

--
John L Stewart

It mystifies me why anyone would even consider building a Circlotron
using a pair of 211 output tubes.
Suppose they run in class A for 40Watts PP. In a normal PP amp with 2
x 211 in class A, you'd need 40k a-a load. 40W into 40k = 1,265Vrms
anode to anode, so anode to cathode signal of each tube = 632Vrms. In
class A, each tube "sees" a single ended load of around 20k.

In circlotron config with the SAME 20k per tube, the same V-k of
632Vrms exists. Each tube is connected so that its 632Vrms is applied
to a winding with 1/2 the turns of the PP transformer meant for
ordinary PP operation. Because there are TWO PP 211, each tube is
arranged so that one is turning on and the other turning off and the
OPT primary has a load of 10k. There will be 316Vrms of opposite
phases at each anode and cathode of each tube. If the gain of 211 is
say 6x, then 53Vrms is needed between grid and cathode of each 211, so
the driver stage must produce two phases of 316Vrms + 53Vrms =
369Vrms. grid to grid drive is 738Vrms.
To achieve this, a couple of EL34 in PP triode with a 1:2 IST might be
used to make 369Vrms anode to anode, and the tranny steps this up to
738Vrms. The EL34 would need 41Vrms grid to grid and then one might
need 2 more stages of 6SN7 LTP and input tube to get things to be
sensitive enough.

So, I have laid out what could be the possible voltage numbers, and
the original poster might like to do his own calculations to see if he
agrees with mine, and then analyse his Plitron OPTs to see what is
actually possible or not. I've assumed class A operation, but that
could be class A1 or A2.
Class AB1 or AB2 is also possible, with the latter using a far lower
RLa-a.

The Plitron data sheet for the OP's OPT 414900 shows the primary is
across terminals 1, 2 and 3, with 2 being CT for B+ and 1 and 3 being
anode terminals. The load RLa-a is given as 8k0, and power stated to
be 150W which is 1,095Vrms across 8k0, and perhaps one might get 150W
in class AB2, or also get what I said above in class A if the load
value is high, or the secondary windings are arranged to ensure the
anode to anode load is perhaps as high as 40k0 as I mentioned, for
class A, when PO is a heck of a lot less than the gut busting AB2
power of 150W.

The 8k0 used in circlotron mode with normal secondary load matching
would give similar performance to using 10k as I mentioned above. The
OPT primary may have its CT taken to 0V, and each 211 would need a
floating 1,200Vdc supply. From a brief inspection, circlotron
operation does look doable, but the 211 grid drive sure needs to be
very well made, using IST capable of 6 times more voltage than if the
211 were simply set up conventionally. I'd would suggest the
distortion produced by the driver stage could be quite high with
circlotron and more than that produced in the output stage because it
has 50% of the anode to cathode signal fed back at each cathode. So
the circlotron should have quite low Rout without global NFB. The
driver stage is not subjected to a changing load impedance of a
speaker, and so its IMD is kept under control. To my mind, the best PP
driver is with EL34 OR KT66, OR 300B with IST and Ea at about 420Vdc,
and Ia at 20mA at least.
With 1:2 IST, Va-a produced by driver triodes is 369Vrms, so 184Vrms
at each anode, ie, 260V peak, and for low THD the maximum possible
should be more, maybe 350Vpk, which seems possible.

Patrick Turner.