[Central-Electronics] Your thoughts on the 20A .....

[George Maier]

Hi Theo and welcome!

There's no doubt in my mind that Jim, WD5JKO, is probably the greatest sage
in the group when it comes to 20A's, and has given you some great pointers.


My personal interest is in keeping the rigs stock, and I've been messing
with them for about 20 years. I've been running filter rigs since the 1960's
(Collins, Drake, Ten Tec, etc) then came to my senses and started enjoying
these simple but elegant phasing rigs  I can honestly say it's incurable.
You should download everything you can on the 20A from BAMA, especially the
factory revs.  There are not too many, but some are helpful.   

You will need a good audio oscillator and a scope as a minimum to do a
complete alignment.  A freq counter and general coverage receiver are great
assets also.  The CE MM-2 monitor scope is a very nice addition if you can
find one.  

As for the VFO's I have several of the BC-458 variety, and have found that
only way to really tame down the drift requires total replacement of all
passive components, and moving a few things around, like that big resistor.
If you can find a Lakeshore Bandhopper VFO, grab it. They are quite stable,
and go all the way up to 10M.  

The 75A-3 is good match, and it's a piece of cake to clone the product
detector from the 75A-4 in a minibox that fits in the FM detector socket.
All you need to do is couple the BFO to an unused pin on the FM socket, and
run a jumper on the mode switch to activate the BFO in FM position. Add a
little hang AGC action with a cap and diode, and you'll think it's an A-4. 

The other option is a CE model A or B slicer connected to the FM socket. The
CE Slicer is phasing demod, and sounds super.  

By the way, don't discount the 10A & 10B either.  Yes they use plug-in
coils, and yes they only put out half the power, but I can drive the 600L
almost to full output with one. 

So, go out and get one, and join the fun, Theo!!

73, George - K1GXT


-----Original Message-----
From: central-electronics-bounces at mailman.qth.net
[mailto:central-electronics-bounces at mailman.qth.net] On Behalf Of K4MO
Sent: Friday, June 16, 2006 5:40 PM
To: central-electronics at mailman.qth.net
Subject: [Central-Electronics] Your thoughts on the 20A .....

I have always wanted to own a 20A, so I am thinking about indulging that
lust and shopping for one. I want to be able to really *use* it, not just
set it on a shelf and talk about it.

I will mate it with a 75A3. 

Frankly, I have never even seen one in operation. How do they perform? How
stable is the "matching" VFO? Isn't it some kind of modified military piece?
As boat anchor go, are they fairly reliable? Do they need a bunch of mods to
get decent audio?

Thanks in advance & 73,
Theo K4MO
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