Vivacious Valves

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Wavemeter
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Vivacious Valves

Post by Wavemeter » 13 Mar 2019, 20:36

I’m appealing to all you great minds to help me with my thoughts on the making of a SUPERHET valve receiver suitable for A model boat. You see I have an idea that I would like to make a predominantly valve radio set up in a vintage format. Those wonderful 1940s photographs showing model boat hulls Absolutely stuffed with all the gubbins that made them work. Most designs of the time where of course Super Regen receivers using usually a single valve. I’m thinking that if I were to obtain a small broadcast valve radio. Dismantle the front end and insert a crystal oscillator It should be possible to turn that radio into a really good superhet Model receiver? My problem is that most domestic broadcast receivers have an internal frequency of 455 kHz. If I want to use 27 MHz ( my preferred frequency band ) Then I would need it to operate at 470 kHz. Therefore my question is it possible to re-tune the internal frequency of the broadcast receiver to operate at 470kHz hopefully without modification to this part of the circuitry?
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Wavemeter
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Re: Vivacious Valves

Post by Wavemeter » 14 Mar 2019, 09:12

Further thought ....I know quite a few of you are Radio Hams like me (G6CVC)
Would it be possible to use my Icom IC751 Hf transceiver as an RF generator to accurately set an intermediate frequency of 470kHz??
It certainly covers that frequency - I realise I’d have to crank it right down and induce the signal
But the frequency counter appears to be really accurate
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Mike_K
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Re: Vivacious Valves

Post by Mike_K » 14 Mar 2019, 12:41

Hi Jonathan

I'm a bit confused about what you're trying to achieve, but not being a radio ham or a rf expert, it is probably down to me.

If you are trying to build a replica of a 1940's R/C set, as you say they were all carrier wave Tx with super-regen Rx, ie they either just transmitted a CW or not at all to control the off/on. The only commercial UK sets were the Mercury Cossor, ED and ECC Telecommander which were all just CW. There would be no point in using a super-het Rx with these Tx as they didn't use xtals and relied on a LC tuned oscillator so were not at all precise. And I think they used super-regen Rx as you could tune it to a wider frequency range and get a bigger gain by using positive feedback with a variable pot.

Or are you trying to use a more modern Tx and then build a valve super-het Rx, so it can be used with other 27MHz sets in operation at the same time? And you would like to base the Rx on a commercial audio receiver? I don't understand why you couldn't use an intermediate frequency (i.f.) of 455 kHz? Many (most) 27MHz R/C receivers use an i.f.of 455KHz, with the Rx xtal being 455KHz less than the transmitted frequency. But I'm probably telling you "how to suck eggs".

Wouldn't it be easier just to copy a late 1950's commercial valve super-het Rx design? I can't remember which manufacturer made them, I think it was Citizenship (and our friends in America call them tubes, not valves). I'll look through my scanned manuals and circuits tonight to see if I can find a circuit for you.

Cheers

Mike

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Wavemeter
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Re: Vivacious Valves

Post by Wavemeter » 14 Mar 2019, 23:08

Hello Mike!

Thank you for responding - you’re nearer the button with your second paragraph, I want to build a proportional outfit compatible with modern 27mhz am transmitters . So 470kHz crystal separation - crystal oscillator front end and a digital decoder spliced on the back end, this in turn driving a steering servo made of an old clock insides with a feedback pot linked to it, the TX initially will be throughly retro on the outside with an 1:8 wave antenna some chunky BBC knobs and levers on Black paxolin mounted on the top side of a walnut box about the size of a car battery. The insides modern . So a retro Hybrid radio gear. I can get hold of a very compact superhet valve broadcast radio for £20 and it seems ideal, Don’t want to go to trouble if making whole RX just splice some bits together
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Wavemeter
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Re: Vivacious Valves

Post by Wavemeter » 18 Mar 2019, 11:43

Actually 455khz is correct I had made an error there
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