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Re: [Amps] Modulation Transformer(s)

To: "k7fm" <k7fm@teleport.com>, <amps@contesting.com>
Subject: Re: [Amps] Modulation Transformer(s)
From: "Mike Sawyer" <w3slk@uplink.net>
Date: Sat, 19 Feb 2005 20:46:38 -0500
List-post: <mailto:amps@contesting.com>
Colin,
    I have to disagree. I managed to find a VM-4 multimatch mod transformer 
for $40, (and that wasn't E-bay) If you can't find a multi-match transformer 
in the 300-500 watt range, (even though you only need 250 watts of audio for 
500 watt plate modulated), You can get buy using a mod transformer from a 
T-195 transmitter from (un)Fair Radio. The nice thing about them is they 
have a tertiary winding to modulate the screen if you are planning on using 
a tetrode.
Mod-U-Lator,
Mike(y)
W3SLK
----- Original Message ----- 
From: "k7fm" <k7fm@teleport.com>
To: <amps@contesting.com>
Sent: Saturday, February 19, 2005 8:25 PM
Subject: [Amps] Modulation Transformer(s)


First, this is an amplifier question - even though the amplifier part in
question is from a class c amplifier rather than a linear amplifier.

One of these days I plan on building a 500 to 600 watt plate modulated rig.
I have all the parts except the modulation transformer.  Finding a 300 watt
transformer normally involves the expenditure of about $150 or more.  I am
considering another option - that of using 2 modulation transformers from an
ART-13 in parallel.

The normal arrangement in an ART-13 is P-P 811 tubes modulating an 813.
What I would propose is P-P/parallel 811 tubes modulating push-pull 813s.  I
realize that there may be no real advantage to running the 813s in
push-pull, but I have the parts and it sounds cooler (only for one band, so
bandswitching is not an issue).

I already have the ART-13 transformers.  They are beauties.  The additional
advantage of the ART-13 transformers is that there is an extra winding,
which would be used for feedback to the earlier stages to reduce distortion.

I have hunted numerous books and never found it discussed.  Anyone done it
before.  Any concerns?  Are resistors needed to match loads?

73,  Colin  K7FM


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