[AMRadio] surrogate modualtor for the 32V


Jim candela jcandela at prodigy.net
Sun Jan 22 14:08:17 EST 2006



Craig,

   The Collins folks will cringe at the thought of "hacking up" a 32V2/3. I
prefer to "hack up" Johnson gear. I did something similar to Steve on a
Viking I. I used a higher power multi-tap modulation transformer (Stancor
120 watt unit) as a choke, picking the taps for the greatest inductance. I
then used a hi-fi tube audio output transformer from a Harmon Kardon
Citation V amplifier. This iron was rated at 40 watts down to 7 hz, so I
figured it would handle lots more at 100 hz and above. I used a 600 watt
Crown (M600) amplifier to drive things. One problem with my approach was
that my voice was asymmetric, and the big Crown was DC coupled. This
resulted in a high amount of DC current flowing in the transformer primary
(8 ohm tap to common), and saturation was evident. The fix was to AC couple
the Crown to the transformer. I used two 10,000 Uf 100 VDC capacitors in
series with the + sides together to in effect make a poor mans non polarized
capacitor valued at 10,000 uf (not 5000). These big caps are a near short
when reverse biased, so the series cap equation does not apply. Thereafter
it worked like a hose...even at 200% positive peak modulation!

Regards,
Jim
WD5JKO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net]On Behalf Of Craig Roberts
Sent: Sunday, January 22, 2006 11:28 AM
To: Discussion of AM Radio; wa5bxo2005 at pctechref.com
Subject: [AMRadio] surrogate modualtor for the 32V


Many thans for your reply, John.  I've noted from the published specs
that the driver and modulation transformers in the 32V-2 are rather
restricted in audio bandwidth, too.  Perhaps Steve Ickes' approach is
worth exploring:

http://www.amwindow.org/tech/htm/obmod.htm

I have a very nice Ashly preamp/EQ/compressor/limiter and 120 Watt audio
power amp that might work very well as a surrogate speech amp/modulator.
Has anyone tried Steve's scheme?

VY 73,

Craig
W3CRR
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