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Old 31st Jul 2021, 2:38 pm   #32
regenfreak
Heptode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Quote:
I have been reading this with a great deal of interest. Back in the early 60s I came across an article in the American Magazine "Radio Electronics April 1953" for a Long Distance FM tuner. having nothing better to do I decided to have a go at building this (fools rush in etc..what did I know about FM radio construction) My boss at the time, Bob, reckoned that we could do it together. It took about 6 months as we had to import a couple of valves from the US.After much faffing about getting it stable (lotta gain built in) we finally had it running very satisfactorily. Its performance was quite startling, no good for FM stereo as IF bandwidth was quite narrow, but with the proverbial piece of wet string as an aerial, any signal passing was sucked in. When connected to a serious 8 element FM aerial long distance continental FM was eminently possible especially with Sporadic E conditions. I, in particular, learnt a great deal about RF earthing, component, positioning, screens across valve bases which has stood me in good stead in my later life, especially as I am now getting quite good at repairing/aligning Quad FM tuners.
I have looked at that article on page 58:

https://worldradiohistory.com/Archiv...cs-1953-04.pdf

It is a badass project that would require a 5 gang variable capacitor, 6BZ7 cascode with untuned, broadband front end, a rather unusual 6J6 push-up tuned RF amp, 6AH6 tuned RF amp, 6C4 oscillator and 6AB4 mixer. The extra 6AH6 pentode would add lots of gain for DX in expense of more noise. Then there are six IF transformers (back-to-back capacitive-coupled double-tuned IFs) and a cascaded 6AU6 limiter!!!

Last edited by regenfreak; 31st Jul 2021 at 2:50 pm.
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