In article , Ross Matheson
wrote:

John Stewart wrote:
in ,
on Sat, 26 Jul 2003 07:26:24 -0400,
: I just took a look at that article in aX. No need for a hard to get
: double choke. A pair of single 20H PS chokes will work OK.
: One end of each choke is at AC ground while the other
: is at the output AC signal potential. The two chokes are already
: tightly coupled through those connexions. The original inventor
: of the subject circuits objective was to avoid iron cored
: devices completely.

Are you sure? Completely? I obtained the impression it was ungapped and of
small size, but I assumed it still had a core! (Smaller than OPT's, natch
It'd be good to get an impression of what this dual choke looked like ...

Of course he is sure, completely! The two chokes should work just fine,
you might even get away with just one if you have a convenient source at
the correct voltage for feeding the screen of the lower tube. The use of
the double choke cuts down on the amount of iron necessary, since the DC
current for the two screens flows in opposite directions, the effect of
the DC tends to cancel as in a push pull output transformer, eliminating
the need for an air gap, or at least a large air gap. Eliminating the air
gap means less iron is needed to maintain the required inductance.

I suspect that the "dual choke" looked pretty much like a very small push
pull output transformer, with four lead wires exiting the windings.

Someone posted a link to a neat design for an amplifier like the Philips
about half a year ago. Unfortunately I don't remember who the designer
was, or who originally posted the circuit. You can find a copy on my web
pages at this URL:

http://users.rcn.com/jbyrns/stuff/scan0022.png

Notice that the plate current for the tubes doesn't pass through the "dual
choke", and a secondary winding has been added to the "dual choke" to
allow the connection of an ordinary loudspeaker.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/