[AMRadio] Eico 730 Modulation Transformer


Jim Candela jcandela at prodigy.net
Tue Nov 12 07:33:15 EST 2013



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Message: 6
Date: Tue, 12 Nov 2013 05:30:09 -0600
From: john nelson <solarelectricjohn at gmail.com>
To: amradio at mailman.qth.net
Subject: [AMRadio] (no subject)
Message-ID:
    <CAFDCxyQmywNvpQi=9sLPgyN7bPpQf9unoiPENwJRdz_pcgrWCg at mail.gmail.com>
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I have a simple question that will be baseline fundamental for most of you
but I have only been into AM for about a year. I than found a Eico 730
external plate modulator amp and in the process of restoring it. The 730 is
in quite nice condition and will be a good stepping stone into plate
modulation and future projects. I plan on using it with a Knight T150 that
has a pair of 6146 and it also has a plate modulation input plug on the
rear of the unit. I do understand the drawbacks of the T150 VFO and do have
a good selection of rocks.

I need some help with the modulation transformer on the 730, It has taps
from 0 ohms to 10 k and I just can't find enough information or the math
involved on what tap I should use to hook it to the T150 plates. Any advice
would be greatly taken I just don't want to smoke her the first time I
power it up. Thanks John W0XAZ



John,

    Take a look at this thread:

   http://amfone.net/Amforum/index.php?topic=27244.msg207633;topicseen#msg207633

   Several folks took a stab at a question similar to yours. This in my opinion is worth printing out and reading over a few times. Bottom line is you want a turns ratio such that the modulation capability hits a desired target. If that makes a plate to plate load impedance that is low for the tubes in the modulator, then either readjust your RF operating point (load to a deeper dip), or add another pair of modulator tubes. Don't let impedance matching be the main concern; instead concentrate on turns ratio, and then deal with the impedances if need be.

Jim
WD5JKO


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