Comments on Central Electronics 20A

Glen E. Zook gzook at HOME.COM
Fri Jun 22 23:50:05 EDT 2001

I am new to this particular reflector but feel I must reply to one of
today's messages.I do not like the practice of "putting down" other
amateurs.  I have always believed that amateurs, in general, are a
trusting, helpful bunch of guys and gals (men and women for the
politically correct among us). I am against the practice of amateurs
"taking advantage" of one another,I am against making "snide" remarks
either to someone.  I am definitelyagainst stealing from another amateur
(or anyone for that matter!),against running up of fictious repair bills
for the purpose of obtaining equipment because the amateur who owns the
equipment can't pay the bill, and similar actions.  Frankly, I have seen
it all!

I am definitely of the "old school" where amateurs help each other. When
the following E-Mail was brought to my attention, I was disturbed.

Date: Fri, 22 Jun 2001 16:06:35 -0500  From: "k5ceg at"

i  see a post a couple of days ago for a modulation transformer for a
central electronics 20 a, i am wondering if i missed something.maybe
this phasing type exciter had such a thing??? i have 6 of them and cant
seem to locate 3 modulations transformers in them.or maybe this was a
mistake by someone that held a conditional class license or something.3
modulations transformers in a 20a would weigh about 50 lbs or i
missed informed or what??? or maybe one needs to go back to

The Central Electronics Model 20A is one of the first SSB transmitters
produced commercially in the United States.  Using a pair of 6AG7 tubes
in the final amplifier, it produces a maximum output of 20 watts PEP.
This is a complete transmitter, including power supply, utilizing
"phase" type generation of the SSB signal instead of the now, more
common, "filter" generation.  However, the 20A uses either
crystalcontrol, or, a modified ARC-5 command transmitter VFO. The
Hallicrafters HT-37 transmitter and the Heath SB-10 SSB adapter are
common examples of "phase" generation transmitting equipment

The approximate weight of the entire unit is 40 pounds. Since this
transmitter does not utilitze the "normal" plate modulation scheme,
there is no plate modulation transformer.  However, if there were a
plate modulation transformer, the weight of it would be in the
neighborhood of a pound, or two, because it would only have to provide a
maximum of 10 watts of audio to fully modulate 20 watts This is opposed
to the "over 50 pounds" claimed by K5CEG. When used on AM the signal is
generated by inserting the carrier (unbalancing the balanced
modulator) and was amplified by the pair of 6AG7 tubes which are in a
linear amplifier configuration.

The schematic refers to the two transformers after the 12AT7 "A F
Modulator" tube (their designation) as "Mod Trans" (short for modulation
transformers- part number 27A0-79-3).  From the diagrams in the manual,
appear to be cylindrical in nature, probably about 1.5 inches in
diameter.  I would doubt that they weigh more than about 0.5 pounds,
probably sless.  The SB-10 adapter has two similar transformers in the
generation circuitry (also called "modulation transformers" by Heath -
p/n 51-38). As in the Central Electronics 20A, those in the Heath SSB
adapter are also very small, about 2 inches square by about 2.5 inches
high.  These weigh, in my estimation, about 3 or 4 ounces each, not over
50 pounds combined weight!

The 20A and SB-10 use a 12AT7 as the audio modulator. The 20A manual
does not give the impedances of the modulation transformers, the Heath
manual does.  The transformers are a 1:1 turns ratio with impedance 20K
ohms.  I would think the 20A would be similar.

Therefore, calling the transformers labeled as TR-2 and TR-3 "modulation
transformers" is completely correct. This is the nomenclature used by
Central Electronics and Heath when describing them.

As a direct result of this information, I believe that K5CEG owes some
heartfelt apologies to those persons he has tried to insult with his
comments about needing to go back to school and about their previous
class of license.  Unless, of course, he is admitting that he has to go
back to school and learn how to read the nomenclature on various
manufacturer's schematics, to learn how to properly capitalize his
typing (i.e. "I", not "i"), spelling (uses "excellant" on his web site
instead of the correct spelling of "excellent" when describing equipment
condition on, proper use of the plural noun (used
"modulations" instead of "modulation"), improper verbage (used "missed
informed" instead of "misinformed"), and so forth .  If that is the
case, I am sure that the Paris, Texas, school system has adult education
classes that he can attend for the purpose of expanding his knowledge.
If he did not mean this action for himself, then I again appeal to him
to offer his apologies.

Because I am new to the reflector, I was asked by some "older" members
to take a look at K5CEG's comments and make my own comments on them.  I
have only met K5CEG once, and I am fairly sure that he does not want me
to reveal the reason and the results of that particular meeting.

Again, I am from the "old school" where amateur radio operators help
each other, not try to hurt each other.  So, let's do our best to try
and help each other rather than "tearing each other down".  How about

Glen, K9STH

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