Small world:
I have the same 70 watt modulation transformer I think. It's for an FAA AM
transmitter too. Two 6146's in the modulator side to one 4x150. Also has a
tertiary winding for the PA screen. The idea here is to modulate a single
4-65a. It's the only glass tube I could find that matched the load
impedance and has a screen grid too. If you can think of another glass tube
that might match up, please let me know.
I had the schematic for the transmitter (TV 6?) too but lost it somehow. I
do have the pin out for the iron. If I remember correctly the transmitter
was made by GE but don't quote me.
73's
Greg
WA7LYO
Kinston NC
----- Original Message -----
From: "Barrie Smith" <[EMAIL PROTECTED]>
To: "Discussion of AM Radio in the Amateur Service"
<amradio@mailman.qth.net>
Sent: Saturday, December 01, 2007 5:12 PM
Subject: Re: [AMRadio] Building
----- Original Message -----
From: "jeremy-ca" <[EMAIL PROTECTED]>
To: "Discussion of AM Radio in the Amateur Service"
<amradio@mailman.qth.net>
Sent: Saturday, December 01, 2007 2:45 PM
Subject: Re: [AMRadio] Building
----- Original Message -----
From: "Barrie Smith" <[EMAIL PROTECTED]>
To: "Discussion of AM Radio" <amradio@mailman.qth.net>
Sent: Saturday, December 01, 2007 2:27 PM
Subject: [AMRadio] Building
Well, I was building a new HV power supply, until I had my gallbladder
taken out last week! Not supposed to lift anything over 20 lbs for a
month.
It's a resonant-choke supply. I was just to the point (with a bunch of
taking out and putting in of parts) of drilling the mounting holes and
finishing it up.
Now (due to a wonderful fellow on this list, whom I'll name if I get
permission), I'm going to start working on an RF deck using a pair of
VT-127As.
These tubes are a cross between a 100TH and the 250TH in a small,
strangely-shaped envelope. Should be just right for 300 easy watts out.
They are a 100TH repackaged for radar use in WW2 and use a 250TH filament
for sustained peak emission. It was also designated the 100TS by Eimac.
An OT ham down the street from me in the 50's ran a pair at 1KW input on
20 CW, it was fun watching those plates glow!
Now I'm thinking about a modulator.
Why not 2 more 127A's? With a window in the rack panel you can watch the
plate color with modulation.
Carl
KM1H
Carl: Thanks for the response.
Well, I did think of that, but I'm kind of at loose-ends here as to what
to do about a moulation transformer.
I have four modulation transformers in the junk box. One is a very
conservative KW PWD, which is large and heavy (I used that in a PP pair of
450THs, modulated by a pair of 304TLs, a long time ago. That transmitter
made a heap-of-smoke . . . and RFI). Another is a National that says 70
watts. It came out of an FAA transmitter, built by National, that used a
pair of 4-65As in the final.
I also have a modulation trasformer that came out of a 250 watt Gates BC
transmitter. And, a Thermadore, that I can't seem to find any information
on.
The KW PWD is rated for 800 watts audio 40 to 7500 hz. It has no air-gap,
and is to be used with a matching reactor and cap, which I have.
The primary is 12,000 ohms, center-tapped. The secondary is 4545 ohms.
I'm mentioning these figures because it's been at least 15 years since
I've calculated various tubes and voltages for matching up modulation
tubes and transformers.
I do remember that on the 450THs I was running 2500 volts @ 600 ma. Don't
remember what the modulation voltage was.
73, Barrie, W7ALW
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