----- 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
Well, you certainly have a nice stash there.
There are probably enough Gates owners on here that can tell you the specs.
However you can determine the turns ratio with a bit of LVAC on the primary
and then calculate the turns ratio.
Old Handbooks, especially the "Radio" version have extensive charts of the
PP load of most tubes used a modulators and you already know that the
VT-127A's are basically 100TH's so you can easily determine their load
impedance. If you loaf them at 500W input using say 1700V @ 300ma for
instance (rounded off) the mod xfmr secondary must be close to 5666 Ohms.
Then knowing the PP load of the modulators and the turns ratio of the xfmr
you can determine what works.
If you want to run some numbers by me by all means do so.
Carl
KM1H
______________________________________________________________
Our Main Website: http://www.amfone.net
AMRadio mailing list
List Rules (must read!): http://w5ami.net/amradiofaq.html
List Home: http://mailman.qth.net/mailman/listinfo/amradio
Help: http://mailman.qth.net/mmfaq.html
Post: mailto:AMRadio@mailman.qth.net
To unsubscribe, send an email to [EMAIL PROTECTED] with
the word unsubscribe in the message body.
______________________________________________________________
Our Main Website: http://www.amfone.net
AMRadio mailing list
List Rules (must read!): http://w5ami.net/amradiofaq.html
List Home: http://mailman.qth.net/mailman/listinfo/amradio
Help: http://mailman.qth.net/mmfaq.html
Post: mailto:AMRadio@mailman.qth.net
To unsubscribe, send an email to [EMAIL PROTECTED] with
the word unsubscribe in the message body.
