Looking for advice on FM regen receivers

[lloydwells]

Ok I have a fairly hefty collection of 1930s radios mainly Philips sets I'd really like to build a little FM regen tuner to plug in to these things obviously such things didn't exist in the early 30s but I'd like to build something in that style. I've found a lot of designs that use the likes of the 12au7 has anyone ever done such a thing using two 30s triodes instead of a double triode and is it possible ?

[G6Tanuki]

If you want it to work at VHF then you could do it using an Acorn triode; alternatively one of the "horned wonder" Octal-based triodes as used in the WS19 "B"-set (CV6/DET20/VR135/E1148) ??

[regenfreak]

1930s domestic radio triodes are ill suited for FM with their large Miller capacitance

[kalee20]

Regen probably won't be up to much - but super-regen can work amazingly well.

I'm currently developing a SR front end, in parallel with another person from another Forum, using ECC81. (ECC82 dies actually work, but as it's low-μ and also lowish ra, it is not so good).

This is not a bad place to start!

[G6Tanuki]

What about a Fremodyne? It has the advantage that - unlike a classic super-regen - it doesn't radiate quench-frequency-modulated "sharsh" across the frequency you're trying to receive.

https://www.radiomuseum.org/forum/fr..._detector.html

[kalee20]

Nope. But it does radiate across ANOTHER wide frequency band.

And if a SR is preceded by an RF amp, then it provides isolation from the oscillations to the aerial anyway.

[G6Tanuki]

The big problem with a *tuned* RF-amp ahead of a superregen detector is that the inevitable stray-coupling from the superregen-stage back to the tuned-circuits of the RF-amp cause those tuned-circuits to 'ring' at signal-frequency which causes all sorts of desense issues.

This problem - along with on-frequency radiation - was why during WWII the "superhet-superregen" - a superhet front-end followed by a superregen detector at IF - was used extensively in airborne RADAR/IFF-type applications.

There's a book - "Super-regenerative Receivers" by Dr. J.R. Whitehead (Cambridge University Press, 1950) that documents a lot of the work done by TRE Worth Matravers during WWII. In times-past when I could call upon the British Library's lending-services and charge the few-shillings to my expenses I got hold of a copy.

Fascinating! Alas after a few weeks I had to return it.

[G6Tanuki]

Could also be worth looking here: http://downloads.bbc.co.uk/rd/pubs/reports/1951-07.pdf

which is a BBC report on a few immediately-post-WWII German super-regen VHF broadcast-receivers. Includes circuit-diagrams.

[Argus25]

I'm not sure if you are aware of a certain radio, the National 1-10A

These have a stage of tuned RF a self quencing superregenerative detector and an audio stage. With the plug in coil set it covers 27MHz to over 250 MHz. It contains an Acorn valve. The radio can run off batteries or a mains psu.

One interesting thing about these sorts of radios is they demodulate AM, but FM too, due to slope detection.

Google search National 1-10A for images, you will see the radio and its schematic.

It would be an excellent framework to model a superregenerative valve radio on. They did a really nice job making it, I have one with the full coil set, it really is quite a marvel. And to make something along these lines I think would be a very rewarding exercise.

.......actually I just got my 1-10A radio out to have a look at it again. "They did a nice job on it" is a total understatement, the design & build is inspirational in my opinion.

Hugo.

[Skywave]

If you want to build a super-regen. that is simple, small and cheap - but not in period - you might like to consider one using the ubiquitous 2N3819 FET. Such a design appeared in 'Practical Wireless' many years ago. I built a few of those: one aimed at the 2m. AmRad band - and they worked quite well.

Al.

[Sideband]

Originally Posted by lloydwells

I've found a lot of designs that use the likes of the 12au7 has anyone ever done such a thing using two 30s triodes instead of a double triode and is it possible ?

As stated, it's unlikely you'll get a standard 30's triode to work at VHF. Acorn valves are fairly cheap and plentiful and will work at VHF. As to whether you can find a suitable circuit for an FM regen using one or two of these is another question.

The ECC81 (12AT7) will probably work OK....the ECC82 (12AU7) was not really designed for RF work.

[kalee20]

Originally Posted by Argus25

One interesting thing about these sorts of radios is they demodulate AM, but FM too, due to slope detection.

They do work with FM, and well, too.

The concept of taking a single ECC81 triode, adding an LC tuned circuit, three other R's, four other C's, and having 100mV of entertainment-quality audio to feed straight into an AF amplifier (all for <3mA HT drain, and without even a whip aerial) is completely awesome.

It's only eclipsed by the thought of the horrendous maths needed to analyse what's going on. The idea of examining the behaviour of a circuit tuned to 100.08MHz taking a sample 80,000 times a second of a "100MHz" signal with instantaneous frequency varying from 99.925MHz to 100.075MHz, is not something I've been eager to tackle. But it hasn't stopped me experiencing the awe of the previous paragraph.

[Argus25]

Originally Posted by kalee20

It's only eclipsed by the thought of the horrendous maths needed to analyse what's going on. The idea of examining the behaviour of a circuit tuned to 100.08MHz taking a sample 80,000 times a second of a "100MHz" signal with instantaneous frequency varying from 99.925MHz to 100.075MHz, is not something I've been eager to tackle. But it hasn't stopped me experiencing the awe of the previous paragraph.

Some years ago now I read the analysis of the super-regenerative receiver published by Ataka, which I think was the definitive work, but Armstrong invented it (from memory I think).

It is extraordinary, if somewhat totally remarkable, that a single triode (or transistor) can be configured in a way to provide so much signal gain that it represents at least 5 to 8 stages of conventional amplification. Albeit a little tricky to adjust with lots of noise in the absence of a received carrier.

Yet, the simplicity of the idea was not ignored by developers of modern tech and super-regen remains in many car remote and garage door receivers and other automation products. Also, cheap children's walky-talkies work this way.

Anyway, you are quite right, the whole notion of super-regeneration, is mind blowing and somewhat resistant to mathematical analysis or easy understanding of how it works (even sans the few glasses of Chardonnay before trying to examine it).

So it makes it more intriguing as a circuit technique and dare to say even "magical", which makes it very attractive to me. The world might get boring if everything turned out to be easy to explain.

cheap children's walky-talkies work this way

And the same bit does transmit, marvellous. Don't forget the single valve radio control stuff from the 50's, valve receiver in a model aircraft.

[Argus25]

I think its a good idea when planning to build a radio to look at the work of the Masters and become the apprentice.

It is easy enough and quick to throw a transistor or two together on some proto board and receive stations, but really that's not a "Radio"

A real radio is were everything is considered on the mechanical engineering side of things as well as the electronics. Of course good mechanical stability is critical in VHF systems.

I think National were masters of both. I have attached photos, the two Acorn valves have been removed. One of the acorn sockets needs repair. I have been cleaning the 1-10A radio up and it needs recapping, and it does contain a few molded mica caps could be interesting. A photo shows the coil sets for the 6 bands. The phenolic tube in the rear corner of the RF compartment normally contains two AA cells as a bias battery.

One of the extraordinary things is the National gearbox and tuning dial, the gearbox design is backlash free. The numbers rotate around in the rectangular dial windows by a gear mechanism in the rotating dial. They were hell bent on calibration and there is a chart for it on the front panel.

National used a massive audio inter-stage transformer, seen just behind the gearbox. The extension speaker for this radio contains the audio output transformer for the 6v6, I don't have that or the original power supply so I'm going to make those.

[Trevor]

i would appreciate a schematic with values using an ecc81 or ef91 of a suitable vhf regene
trev

[kalee20]

The link in Post #4 does work, and uses ECC81.

[kalee20]

Originally Posted by Argus25

A real radio is were everything is considered on the mechanical engineering side of things as well as the electronics. Of course good mechanical stability is critical in VHF systems.

I think National were masters of both. I have attached photos...

As you say Hugo, what a thing of beauty! Superb mechanical design and construction.

[ms660]

Originally Posted by Argus25

One of the extraordinary things is the National gearbox and tuning dial, the gearbox design is backlash free. The numbers rotate around in the rectangular dial windows by a gear mechanism in the rotating dial. They were hell bent on calibration and there is a chart for it on the front panel.

That's the famous PW drive, also used in the HRO's etc.....Teeth you can see and get to, the HRO was also elegantly simple both in electronics and mechanics, my favourite receiver from those days, superb tuning and an excellent performer.

Lawrence.

[Argus25]

Originally Posted by merlinmaxwell

And the same bit does transmit, marvellous. Don't forget the single valve radio control stuff from the 50's, valve receiver in a model aircraft.

Yes, it was pretty clever to easily get the super-regen stage to transmit saving all kinds of additional parts.

There were some good published projects for battery valve transceivers, both VHF & UHF, I think the one in the photo used a 1G6 and another valve, had a carbon mic (photo attached) a very cool photo too, he looks like one of the Righteous Brothers.