[AMRadio] Building

Greg bluebirdtele at embarqmail.com
Sun Dec 2 01:46:58 EST 2007

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.
Kinston NC
----- Original Message ----- 
From: "Barrie Smith" <barrie at centric.net>
To: "Discussion of AM Radio in the Amateur Service" 
<amradio at mailman.qth.net>
Sent: Saturday, December 01, 2007 5:12 PM
Subject: Re: [AMRadio] Building

> ----- Original Message ----- 
> From: "jeremy-ca" <km1h at jeremy.mv.com>
> To: "Discussion of AM Radio in the Amateur Service" 
> <amradio at mailman.qth.net>
> Sent: Saturday, December 01, 2007 2:45 PM
> Subject: Re: [AMRadio] Building
>> ----- Original Message ----- 
>> From: "Barrie Smith" <barrie at centric.net>
>> To: "Discussion of AM Radio" <amradio at 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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