Tube FM radion

[johnheath]

For sevetral years I have had a wish to build a tube radio for FM... Thera are a lot of schematics on the internet concerning old AM-radios.

Can maybe anyone here give me some advise on what to build or really anything that can get me started?

In many of the "old" radios they used tubes that are very difficult find to non excisting.

Thanks

/John

 

[joaquins]

Just to be clear, do you want a transmitter or a receiver?

And... Why do you want it? for learning, fun, or you expect to get a better experience, quality or something out of it? I really like tube stereo hifi-ish amps and I have one never saw nobody looking for a tube FM radio, that's why I'm asking.

I'm not in the radio stuff, but I think these are questions that may be useful for answering your question, the more data you aport the easiest is to answer what you are asking.

JS

 

[johnheath]

Hi

Well forgot to mention it... a receiver... just for listening to radio. I do not expect anything hi-fi stuff.

Tube radio just because it is nice to build and nice to watch =)

I have some experience in building various tube stuff like preamps and guitar amps and so on.

/John

 

[PRR]

All of the tubes for almost any FM radio should be readily available. Few of them were "special", most of them were over-stocked when transistors kicked the legs out from under tube radios/TVs, most of that overstock is available from the usual big tube stores.

The COILs are un-obtanium now. While the RF/LO coils may be a few turns around a pencil, the IF cans are fairly tricky and AFAIK we threw all that stuff out decades ago.

Best bet is to collect old hulks from eBay and restore/rebuild them.

IMHO there were 2 or 3 FM tube tuners which really stood-out (and better than 99.9% of the FM transmitters out there), and 3,456 tube FM tuners/radios which were inferior to most of the transistor and chip FM gear. Heat is a big issue. Cost is a BIG issue so most tube FM was barely adequate; tranny designers could be a little more generous, and chip makers had the incentive to do very-good so they could sell at all levels of the market.

Ceramic IF filters also help a lot, are awkward (and were rare) with tubes, common with chips.

If you live near the tower, a 1-tube radio will catch FM. Build a super-regenerative. Tune it a hair to the side of the frequency. Slope detection pulls the audio out of FM. It has no noise-rejection and some THD, but for just one bottle it is sweet.

 

[PRR]

*** Note that superegenerative tuners may not be totally legal. Not banned by type, banned because a superregen almost always transmits a weak signal, near the broadcast frequency (and maybe many others), and that can't exceed a certain level (usually safe if it can't be picked-up outside your fence).

You can add an RF stage to reduce the radiation, but that adds complexity and problems, and it may leak anyway.

 

[abbey road d enfer]

Hi

Well forgot to mention it... a receiver... just for listening to radio. I do not expect anything hi-fi stuff.

Tube radio just because it is nice to build and nice to watch =)

I have some experience in building various tube stuff like preamps and guitar amps and so on.

/John

Building an FM radio is a very different project. You would have to build the RF inductors; it's not very difficult, but adjusting them is difficult. You need specific equipment for that. Then you have to find a 3 or 4-cage variable capacitor; they are long out of production so you would probably need to salvage it. Then you would need the IF transformers, which you can't DIY and you need another specific equipment (a wobbulator).
When Heath marketed kits, the RF head was pre-built and the IF transformers were pre-adjusted IIRC.
Preamps and guitar amps are very predictable; you can adjust them with only a multimeter. RF work is very different; doing it without test equipment is like running a cross-country marathon blindfolded.
I would suggest that you read about the operation of the superhet, analyse the schemos of some commercial products and practice on salvaging tube receivers before eventually taking the endeavour.

http://www.valve-radio.co.uk/literature/leak-trough-line-stereo-fm-tuner-service-manual-and-circuit-diagram/
http://www.vacuumtubeaudio.info/project7.htm

 

[CJ]

https://web.archive.org/web/20131122141438/http://www.jumpjet.info/Pioneering-Wireless/eMagazines/VTV/VTV05.pdf

https://web.archive.org/web/20131122141457/http://www.jumpjet.info/Pioneering-Wireless/eMagazines/VTV/VTV06.pdf

 

[johnheath]

Wow Thanks - When three wise men humbly explains that it will be difficult to very difficult I think it would be best to try to find an old tube radio and try to restore it perhaps?

But could you tell me… I have heard that the "old" tube radios cannot be used to receive todays high FM frequencies like 107 MHz and that is perhaps the biggest concern of all? It is said to me that the tubes and caps must be selected and arranged to handle such high frequencies which would demand a completely new design?

Am I wrong here?

 

[abbey road d enfer]

Wow Thanks - When three wise men humbly explains that it will be difficult to very difficult I think it would be best to try to find an old tube radio and try to restore it perhaps?

But could you tell me… I have heard that the "old" tube radios cannot be used to receive todays high FM frequencies like 107 MHz and that is perhaps the biggest concern of all? It is said to me that the tubes and caps must be selected and arranged to handle such high frequencies which would demand a completely new design?

Am I wrong here?

I believe by 1960 or 61, all european mfgrs had extended the FM range up to 108. I don't know about American and Japanese.

 

[johnheath]

I believe by 1960 or 61, all european mfgrs had extended the FM range up to 108. I don't know about American and Japanese.
[/quote]

So… Would you say that finding a tube radio from the early 60's and make it work would solve my long time wish to get a tube radio? =)

/John

 

[JohnRoberts]

My first piece of hifi gear (1950's) was a FM tuner, and I was so wet behind the ears that I didn't understand why it wouldn't drive speakers, but I finally figured it out, with the help of an amused TV repair shop.

The old school tuner/radios used a variable capacitor to tune stations, literally a bunch of metal plates interleaved with one set fixed, and the other set mounted to an axel that rotated the moving plates up and away from the fixed plates so you could vary the capacitance (and frequency for tuning) .

If an old school tuner does not go high enough  (most likely needs lower capacitance) there may be a mechanical adjustment or capacitor trim. As I recall trimmer capacitors looked a little like small resistor trim pots but with an actual screw in the middle that squeezed some capacitive plates closer together to vary the C.

JR

 

[thomasdf]

If you need specific tubes for a vintage tube radio hit me up, as I have a pretty large collection of them sitting here and not being used.

Cheers

 

[johnheath]

Thomasdf -  thanks… I will keep that in mind =)

John - I know that there are a few adjustable capacitors to buy but they are usually within quite low values of a couple of pF to a couple of hundred pF. Do you have any ideas on the range of those adjustable capacitors you mention?

/John

 

[JohnRoberts]

Thomasdf -  thanks… I will keep that in mind =)

John - I know that there are a few adjustable capacitors to buy but they are usually within quite low values of a couple of pF to a couple of hundred pF. Do you have any ideas on the range of those adjustable capacitors you mention?

/John

I would guess single digit pF but just guessing...

JR

 

[PRR]

US FM tuned to 108 from the "beginning" (after the move from the 54MC band).

I do not know where you found that information. On the internet??

_AM_ has a minor issue. AM was 10KC spacings. Europe switched to 9KHz(?) spacings. Good old manual-tune variable capacitor has no trouble with that, you can tune ANY frequency in the band. But early "synthesized" tuners only hit 10KHz points. In a 9KHz world they will only hit 1 in 10 of the assigned frequencies. Fortunately very few synth tuners were made before the assignments changed, and all later synths have a 9/10 switch/jumper to set them to work in the intended area.

 

[johnheath]

I do not know where you found that information. On the internet??

No, it was said to me by a radio amateur here in my home town

 

[abbey road d enfer]

I do not know where you found that information. On the internet??

No, it was said to me by a radio amateur here in my home town

There was definitely a time in Europe where FM tuners would go 88-104 MHz instead of 108.

 

[Conviction]

I do not know where you found that information. On the internet??

No, it was said to me by a radio amateur here in my home town

There was definitely a time in Europe where FM tuners would go 88-104 MHz instead of 108.

Indeed there was. And as for Western Europe - 87.5-100MHz. I come across such tuners all the time at the local radio museum.
Some of these were probably never meant to end up in Northern Europe. Yet they did.

... Some of these also caused trouble, cause the military used the extended band.

 

[PRR]

One Tube FM Tuner - 1960

 

[johnheath]

Thanks PRR - this perhaps what I wanted… a simple little gizmo to work with. =)