[Hallicrafters] SX-28A "deaf" on higher bands

[T David Cohen]

Many years past, during my novice days, I had an SX-28A and I remember
replacing the RF stage with a plug in circuit that used a 9 pin tube (I
believe it was a 6BZ7 but I'm not sure).  I can't remember the details =
for
the replacement circuit but I'm sure it came from a CQ or QST article =
(that
would have been my only source of information at the time).  It was =
built in
an aluminum "minibox" with an octal plug and the bottom and the 9 pin =
socket
on the top. It made all the difference in the world on 15 meter CW.  The
stock receiver was "deaf as a post."  Someone else is bound to remember =
it.

Dave Cohen, N7TC

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Roy Morgan
Sent: Monday, April 17, 2006 9:52 AM
To: Roger Basford; hallicrafters at mailman.qth.net
Subject: Re: [Hallicrafters] SX-28A "deaf" on higher bands

At 04:27 PM 4/14/2006, Roger Basford wrote:
>...I've just bought a very nice SX-28A receiver... things are very =
quiet=20
>on the HF bands, falling away to very little on 20 metres.


Roger and others,

The 6SA7 mixer tube used in the SX-28's was followed by a better one =
later=20
on. A plug-in mod is to replace the 6SA7 first mixer with a 6SB7 for =
better=20
performance on the upper one or two HF bands.  You may need to do a =
small=20
bit of alignment, but it should work better at the higher frequencies as =
is.

(In Rogers case, apparently *all* the HF bands are weak, so that points =
to=20
other difficulties.)

I cannot remember if the 6SB7 is built with the low loss base (tan =
instead=20
of black) or not.  If not, I also don't know if there is a 6SB7-Y which=20
would be the low loss base version.

My SX-28's are some ways from overhaul, so I would be glad to hear =
results=20
from  anyone who tries this change.

Roy



- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-948-6213
roy.morgan at nist.gov --

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