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Old 17th Feb 2015, 9:18 pm   #13
Phil G4SPZ
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Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,385
Default Re: Trio 9R-59DS communications receiver (1970)

Thanks again chaps, some really interesting observations and suggestions there.

I'm disinclined to undertake the major mods that David so usefully listed, mainly because I do prefer originality and have been aiming to get this set running as it would have done when new. But having said that, in reality the drift is a bit of a pain, so I'd like to improve that aspect of its performance if possible. Turretslug's suggestion is one I'll definitely pursue, but I want to do a few tests regarding mains variation and frequency stability. I have a 160 VA constant voltage transformer so I'll try that out first. It seems to be the case that Trio were trying to appeal to the true well-established amateur radio spirit of home construction, and so they actively encouraged modification, which was perfectly acceptable at the time - once the radio was out of guarantee, of course! Not so nowadays with the usual 'no user-serviceable parts inside - opening case invalidates warranty' statements and three pages of Health and Safety warnings at the front of the handbook. With the passage of the years, however, I suspect many of us would now strive to preserve originality, rather than modify a vintage radio, even if a performance improvement resulted.

One interesting difference emerged between the original user manual that came with the set, and the copy I downloaded from the internet. The original paper copy (presumably earlier) manual includes a valved crystal calibrator, and this is the version of the circuit that the previous owner built into the set. The downloaded (later) manual substitutes a transistor circuit.

Notwithstanding the frequency drift, which as Terrybull so nicely put it "keeps you awake whilst listening", this receiver has been giving me some excellent CW and SSB signals on 40 metres all day, on a very modest random wire antenna. With a resonant antenna, properly matched, I'm sure it would perform even better.
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