A plethora of vintage PCB's

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Pchristy
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Re: A plethora of vintage PCB's

Post by Pchristy »

You might want to have a look at the Norcim website. Lots of good stuff on there! The early pages deal mostly with Micron stuff - not surprisingly as it was founded by Terry Tippet, of Micron fame! But later pages have lots of vintage RC circuits. Page 19 has both transmitter and receiver circuits for the RCS Guidance System Mk2.

https://www.norcim-rc.club/

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Pete
flea_flyer
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Re: A plethora of vintage PCB's

Post by flea_flyer »

Thanks Phil. Just checked it out.
Gerry
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Re: A plethora of vintage PCB's

Post by flea_flyer »

Well, I decided to re-purpose the RCS 27MHz electronics and fitted it into a second-hand aluminium enclosure, together with battery , on-off switch and microswitch button. Good strong output signal. I'm u sing a 1.2m telescopic antenna, but the RCS Guidance System MkII tx used a centre-loaded antenna. I now need to figure out the best way to add a centre-loading coil. I've got a "Rig-Expert" Antenna Analyser (very nice bit of kit, by the way) which should make the job of setting up the loading coil a bit easier.
Here are some pictures of the transmitter. The battery is made up of two spare 'Eneloop' flight packs connected in series, giving a supply of about 11V when fully charged.
Next project was to have been to construct a Singlet super-regen receiver, but I may try and re-tune an early OS receiver that I have somewhere.
Thanks to all who helped.
Gerry
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PaulJ
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Re: A plethora of vintage PCB's

Post by PaulJ »

'Lovely job Gerry, it's nice to see it being "recycled" instead of put in the skip! :oops: .

Paul
Pchristy
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Location: South Devon, UK

Re: A plethora of vintage PCB's

Post by Pchristy »

Might be easier to add a base loading coil, rather than centre loading. Around 2uH should do the job for 27 MHz.

There's a handy whip aerial calculator here: https://daycounter.com/Calculators/Whip ... ator.phtml

For the diameter, use the average (telescopics vary from base to tip).

I was never a fan of centre-loaded aerials, as only the bit above the coil seems to radiate. Up to 1/4 wavelength, I'm a firmer believer in the old loudspeaker rules - "The bigger the better!" :)

Also, base loading is less prone to damage, and makes the aerial easier to replace!

The coil doesn't need to be anything special, as the Q will be fairly low anyway. A moulded choke of appropriate value would probably do nicely.

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Pete
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Re: A plethora of vintage PCB's

Post by flea_flyer »

Pete
Thanks - your comments make a lot of sense. I'll try a base loaded antenna
Gerry
flea_flyer
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Re: A plethora of vintage PCB's

Post by flea_flyer »

My last post in this thread was a long time ago, but I'm after some more help, so here goes!
Having successfully "re-purposed" the RCS tx board from PaulJ as a way of bypassing scratch-building a Singlet Tx, I was intending to build a matching Singlet super-regen receiver. However, this has caused me quite a bit of trouble, so that the project has gone nowhere, mainly due to dealing with obsolete germanium PNP transistors in a circuit where I'd prefer to use more modern silicon NPN devices. (In a straightforward amplifier circuit, I think I could have handled updating the bias resistors, etc, but with a super-regen circuit, this was always going to be problematical.)
Does anyone have a spare old super-regen tone receiver or circuit board to go with my RCS Tx? It would be nice to have one that was part of the RCS set, but it may have to be a case of "any port in a storm".
I checked the RCS Tx output/carrier frequency - it is 27.125MHz, but I suppose that is not critical for a super-regen rx?
Gerry
Pchristy
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Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: A plethora of vintage PCB's

Post by Pchristy »

A 27 MHz Rx will pick up anything between 26 and 28 MHz, though it should be tuned to match the transmitter for optimum range.

27.125 MHz sat squarely in the middle of the old 27 MHz band, and was often used in Txs intended for use with super-regen receivers.

Germanium transistors can still be found, for example: http://www.timetravelaudio.co.uk/shop/c ... ansistors/ and can perform well. One of the best rated receivers of the late 60s / early 70s - the RCM Classic - used germanium transistors. The only place I would recommend silicon replacements in an old design would be in the output switching stages.

Super-regen receivers are something of a black art! There were lots of proven designs around, but many used tiny transformers in the audio stages - even rarer than germanium transistors nowadays!

You should be able to find a MacGregor Minimac or RCS receiver kicking around somewhere. I was always a big fan of the Minimac, using one for years with few problems. And, of course, there were lots of designs for receivers published in past issues of RCM&E.....

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Pete
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PaulJ
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Re: A plethora of vintage PCB's

Post by PaulJ »

Gerry, I have pm'd you.

Paul
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Re: A plethora of vintage PCB's

Post by flea_flyer »

Pete
Thanks for your comments. Agreed, the receiver will have to be tuned for best reception on 27.125MHz.
I actually have quite a few germanium transistors amongst my 'black art' sufficiently well enough to do a proper substitution.
Agree too on the scarcity of the miniature audio transformers, especially ones with a 4:1 impedance ratio, which seemed to be quite popular.
I'll keep looking for a used receiver that can be pressed into service....
Gerry
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