I don't have the schematic in front of me, but going by the previously given
link I do recall now it being a discrete diode mixer. Actually, I think there
may be a pre-amp there too, been a while, that might be more of a
buffer/matching section than a high gain block. Will find manual when I dig up
radio again. I think I did use the prescribed PIN diodes but I'm guessing the
unmatched diodes in the mixer is a problem.
I do recall the dial indicator getting sticky and not always moving. Is that a
sign of needing a PTO rebuild?
No RF gain on the Argosy. RF gain would probably be a great thing on 80/40 as
you mentioned.
Shawn Upton, KB1CKT
--- On Sun, 8/1/10, Dr. Gerald N. Johnson <geraldj@weather.net> wrote:
> From: Dr. Gerald N. Johnson <geraldj@weather.net>
> Subject: Re: [TenTec] Argosy 525
> To: tentec@contesting.com
> Date: Sunday, August 1, 2010, 7:07 PM
> I think the tentec of that era that
> preceded the Corsair and Corsair II
> that used a double gate mosfet mixer rather than a diode
> ring and super
> sturdy RF and IF amp stages didn't do as well in strong
> signals. Though
> if the diodes for the switching diodes were poorly chosen
> their loss
> could cause the band pass filters to be narrowed and those
> very diodes
> to not handle strong signals. They shouldn't have affected
> drift,
> possible that's the PTO in need of lubrication or rebuild.
>
> You don't need all the available RF gain on 80 and 40 and
> you make it a
> lot easier on the receiver by backing off on the RF gain
> control so it
> can handle the static crashes much better.
>
> The wrong diodes will not improve the diode switches. True
> PIN diodes
> work measureably better than 1N4007 and 1N4007 work better
> than 1N914.
> There was an article about that in VHF Communications years
> ago that I
> found on an New Zealand ham's web page (I do have the
> original magazine
> too). http://homepages.ihug.co.nz/~jaking/TS-940_02.htm#_Toc155846465
>
> Googling intermod in switching diodes turned up many ham
> and deep
> technical references.
>
> 73, Jerry, K0CQ
>
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