Sun May 13 10:46:53 EDT 2007
is like 180 volts....
There is a pot on the mod deck, in series with some resistors,
and you can just relocate the pot to the hotter end to give
a higher bias voltage.
The range of the pot is not enough to get 100tl,s biased,
although I think I could have used one pot equal to all
the resistors in series....
The bias also keyed the plate through the push to talk,
and I forget how they did that, maybe that is why they did
the resistors and pot.
It went something like this...
o bias source
\ fixed resistor
\ fixed resistor
/...... bias Pot
I just moved the pot to the top of the circuit for 100tl,s
After I blew up the mod transformer, I built a variac input
bias supply on the mod deck, since the mod transformer
was re located to the bottom of the transmitter.
I got a chassis the same size as the original, painted it the same
color, and built a new modulator on it (with the variac bias).
I even put the patent number plates and the Collins plates
I could never hear any difference between 100th's and 100tl's.
Since I ran both a 4-400 and 100th's, I decided to add a separate
filament transformer on the rf deck to just handle the 4-400.
This actually reduced the load on the original transformer since
it only did the 100th's.
Easy to do since the 30k-1 has the connection strips on the back
of all the chassis.
Remember, most of this went on a long time ago, before
the transmitter was worth much.
I did do all the changes nicely, no hack up jobs, and it worked
very well, and sounded good, and looked very nice and stock
on the outside.
It was very reliable.
Its weak point was the links....it had 4 LARGE coils wound on
big ceramic forms, with the swinging links all ganged
and moving at the same time.
You picked what coil was in the plate circuit with a huge
switch, and it had 4 separate antenna outputs, each with
its own link tuning cap in the back.
The links themselves were a little wimpy.
I ran 300 to 350 watts out, and the links would get warm.
Since the thing was made in 1946 (sn 9), the plastic
on the link coils was going, and I had to make one for
The back of the transmitter had a door on it with
slots for air.
I pushed in some rubber grommets and mounted fans
in them, to run at a quiet half speed...to keep things cool.
If I had replaced all the links with something bigger,
no reason not to run 400 watts out.
Very interesting thing about 100th and 100tl tubes.
The ARRL handbook had a mistake they never corrected
over the years.
The books show the 100th as putting out 650 watts in class b,
and show the 100tl as doing 450.
650 watts out is more than the input power!
Both tubes do 450, but the ARRL never corrected it....
> Speaking of the 30K series, I think we spoke about this a
> while back Brett -
> What is the difference between the 75TH and 75TL? I seem to
> recall it was only a
> different bias setting?
> Also, with respect to the 30K-1 vs. 30K-5, I think the only
> difference in in the
> PA deck - mod deck should be the same, so....is there an
> adjustment somewhere on
> the mod deck for setting the bias on the modulators? How much
> of a difference is
> there to use a 100TH instead? I seem to recall you saying
> that you ran 100THs in
> Brett Gazdzinski wrote:
> > In my 30k-1, the 4-125 would glow very bright orange
> > at 2500 volts and 150 ma.
> > The 4-250 would show slight color, the 4-400 would not
> > show any color at all.
> AMRadio mailing list
> AMRadio at mailman.qth.net
More information about the AMRadio mailing list
This page last updated 11 Dec 2017.