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Old 17th Feb 2015, 8:48 pm   #12
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 3,690
Default Re: Trio 9R-59DS communications receiver (1970)

Good to hear that this has been a success after what must have been a demoralising chase in the BFO department- but conclusion makes putting to succesful use all the more satisfying! The forum certainly proved it's worth re. the Q-sapping wax, too- another one for the cranial file. One of the receivers I've been tempted to acquire on occasion if space/time/life permitted- it might be looked down on by some but, as RW highlights, the SWL/amateur scene was rather spoiled by the excellent professional/military receivers available at a fraction of their real cost. After all, a tuned RF and two IF stages make it a radio with intent.

I wonder if the mains-dependency component of the LO drift might be helped by adding the mixer screen-grid feed to the stabilised supply? Long ago, I found through tinkering that this could make a small but significant difference to oscillator stability- after all, changes in screen-grid voltage and effect on electron stream effectively look like a variation in capacitance on the output of the oscillator. It may be slight, but "slight" is still significant for SSB readability at HF. A quick bit of fag-packet maths suggests a 10k (miniscule wattage) feeding the existing 68k from the nominal 150V, rather than the 134V signal valve rail. The extra 1.6mA from this rail shouldn't shift the stabiliser operating window significantly.
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