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

[Roger Basford]

Hi Roy,

Thanks for the info. The RF amp in my 28 is a 6AB7; a 6SA7, I think, is 
B9A-based?

Regards,

Roger/G3VKM

----- Original Message ----- 
From: "Roy Morgan" <roy.morgan at nist.gov>
To: "Roger Basford" <roger at new-gate.co.uk>; <hallicrafters at mailman.qth.net>
Sent: Monday, April 17, 2006 3:52 PM
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 
>>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 
> on. A plug-in mod is to replace the 6SA7 first mixer with a 6SB7 for 
> better performance on the upper one or two HF bands.  You may need to do a 
> small 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 
> other difficulties.)
>
> I cannot remember if the 6SB7 is built with the low loss base (tan instead 
> of black) or not.  If not, I also don't know if there is a 6SB7-Y which 
> would be the low loss base version.
>
> My SX-28's are some ways from overhaul, so I would be glad to hear results 
> 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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