Schematic for tube radio

[ALAND1]

I am interested in building a simple 1 tube AM or shortwave radio. I need to know if anyone has a diagram for such a circuit or knows where I can obtain one.

Thanks

 

[ljcox]

When I was 14, I had a book "Radio for boys". It had circuits and construction instructions for several valve radios in it.

You may still be able to find a copy somewhere.

I can't recall if there was a one valve one in it but I think there was.

Len

 

[Nigel Goodwin]

To use just one valve it really needs to be a regen, or super regen, or to use the same stage more than once (can't remember what that's called?). These types of designs were common place many decades ago, but modern designs are probably non existent?.

You might try doing a search on google, you will probably find something suitable?.

 

[awright]

1 tube radio

Why 1 tube, ALAND1?

As a design challenge, for simplicity, for cost, because you have heard it is possible?

Do you mean one stage or one tube envelope? Toward the end of the tube era manufacturers were making COMPACTRON tubes that had three (or more?) devices in a single glass envelope, with each device optimized for a specific function in a radio or TV (RF amp, oscillator, mixer, detector, power amp, etc.). I don't remember the exact configurations and combinations of functions.

I just googled "compactron" and got over 3000 items, one of which was this:

"EB5AGV's One Compactron Receiver pageEB5AGV's One Compactron Receiver page. Keep them glowing! Welcome to the One Compactron Receiver pages. The article reproduced here was publised in the ...
jvgavila.com/compac.htm - 3k - Cached - Similar pages "

Check it out!

awright

 

[ljcox]

The term Nigel is looking for is "regenerative receiver"

There may be a group who refurbish old valve radios that may be able to help you.

Len

 

[Nigel Goodwin]

The term Nigel is looking for is "regenerative receiver"

No, I mentioned regen, this is where you apply positive feedback to just before the onset of oscillation.

The technique I mentioned is where you use the valve (or transistor) as an RF amplifier, then feed to a detector, then feed it back through the same valve (or transistor) and use it as an audio amplifier as well. This gives you two valve performance, with only a single valve (or transistor).

It was a common technique for homebuilt radios, and doesn't have the stability and adjustment problems of a regen.

 

[JimB]

The technique I mentioned is where you use the valve (or transistor) as an RF amplifier, then feed to a detector, then feed it back through the same valve (or transistor) and use it as an audio amplifier as well. This gives you two valve performance, with only a single valve (or transistor).

The technique you are trying to think of is Reflex.

In the late 60s and early 70s there were lots of reflex circuits in "Radio Constructor", a now long dead radio hobby magazine.

Talking of Radio Constructor, whatever happened to Smithy and Dick?
Their modern equivalent must be on this board somewhere!

JimB

 

[Nigel Goodwin]

The technique I mentioned is where you use the valve (or transistor) as an RF amplifier, then feed to a detector, then feed it back through the same valve (or transistor) and use it as an audio amplifier as well. This gives you two valve performance, with only a single valve (or transistor).

The technique you are trying to think of is Reflex.

:lol: THANK YOU :lol:

It was driving me mad trying to remember :lol:

In the late 60s and early 70s there were lots of reflex circuits in "Radio Constructor", a now long dead radio hobby magazine.

Talking of Radio Constructor, whatever happened to Smithy and Dick?
Their modern equivalent must be on this board somewhere!

There's been one recently in EPE, based on the designs of the man who did most of the Radio Constructor designs. I bought Radio Constructor until it ceased publication, it was a decent magazine!.

I used to enjoy Smithy and Dick as well!.

 

[ALAND1]

Thanks for all the replys to my question. I did some more searching on google and found a site that is actually for crystal radio enthusists but also has a kit that can be purchased for building a 1 tube regen receiver that receives signals from the broadcast band thru 8.5 MHZ. If anyone else is interested the web site is www.midnightscience.com

 

[Sebi]

Just for curiousity, here is some audions basic ccts.

 

[JimB]

Sebi,

The circuit "R adjusted feedback-2" has an error.
Lf is shorting the anode to -ve, needs a capacitor.

JimB

 

[mstechca]

I think 1/2 of these circuits can be pulled off with NPN or PNP transistors :wink:

 

[Nigel Goodwin]

I think 1/2 of these circuits can be pulled off with NPN or PNP transistors :wink:

Most (if not all?) of the circuits can be, and have been - but they require changes, due to the low impedances of transistors (mainly using taps on the coils to feed the base of the transistors). By using FET's you can pretty well use the existing configurations, with less voltage of course.

 

[Sebi]

Thanks, JimB - i've corrected. (too many copy/paste :lol: )

 

[john1]

Hi,

I remember playing around with setups like those for years when i was
into that sort of thing. I didn't like having to mount the tuning cap
on insulators from the chassis so i usually had the principal tuning
to chassis, unlike some of those where the tuner is not grounded.
In those days you could buy fairly small high voltage batteries quite
easily. 67 volt and 90 volt packs were fairly common i think.
I don't remember any battery valves that had more than one amplifier
in the same envelope, although i think that diodes were included with
some battery valves. I used to use frame aerials on the sets i made
in preference to normal aerials, i would wind the frame aerial to be
the tuning coil, and include two other individual windings with it
one for the reaction, and one for the audio pick up to be fed back to
the input, i found that an RF choke worked better than relying on the
speaker transformer to act as an RF choke. I also found that by using
diodes to make the audio (detect) and feed it back to the grid circuit
i got better results than by relying on the valve to self-detect.

There are many circuits like that, they all rely on the RF being
superimposed on the audio from the valves point of view, the valve
amplifies both, so you get extra gain from that stage.

There is another reactive circuit which i have heard of but never tried
where the feedback is much higher, but the circuit is prevented from
oscillating by being 'quenched' at a supersonic rate, this is supposed
to give about the maximum gain achievable from reactive circuits.
I don't remember the name for that circuit.
And i doubt its only one valve.

Best of luck with it, John

 

[audioguru]

Hi John,
A regenerative circuit that quenches at an ultrasonic rate is called super-regenerative.
It actually oscillates a little. It is the oscillation plus signal that is rectified by the active device and the resulting DC causes the circuit to be quenched, or squegged, or cutoff. Notice that it is cutoff by strong local signals.
They are normally used to amplify and detect AM signals but can also detect FM by using slope detection where they are tuned to one side of the signal. Therefore the signal frequency changes by FM and slides up and down the tuned slope creating AM out of FM.
A single valve or transistor can do it. :lol:

 

[john1]

Hi audioguru,

I thought it was important that it did not actually oscillate, as this
would 'compete' with the signal.
So that circuit is deliberately made to squegg ?
I never made one of those circuits, and i still don't really see what
makes them give any higher output, but i accept that they do what the
books say they do.
I didn't know a single valve or transistor could operate that weird
circuit.

These days i am still trying to get my head around PLL, about which
i still seem to have some sort of non-comprehension !

Regards, John

 

[audioguru]

Hi John,
The radiated oscillation from a regen and super-regen causes interference to other radios. It doesn't bother itself. Some circuits use a buffer stage to isolate the oscillating circuit from its antenna.
Just before it oscillates the gain of a regen or super-regen is very high due to its positive feedback.

A difficulty that I had in understanding how PLLs work was its loop filter. If you use a "good" filter with a series resistor and a shunt capacitor to ground then the PLL goes haywire. It needs a resistor in series with the capacitor to ground for "damping". The loop filter causes a delay and the voltage controlled oscillator in the PLL overshoots its target and swings wildly around it, without damping. :lol:

 

[john1]

Cheers !

I shall struggle on trying to comprehend
what on earth is better about synchronising an oscillator to a signal
or what possible use that could be, or how it could help in any way,
obviously there is some advantage to it.

Is it easier to amplify ? does it amplify better ? Or is it nothing
to do with amplifying it better but that its much smaller ?

There must be some point to it that i don't see.

**broken link removed**
This explains some of the complexities and none of the reasons.

John

 

[Nigel Goodwin]

Cheers !

I shall struggle on trying to comprehend
what on earth is better about synchronising an oscillator to a signal
or what possible use that could be, or how it could help in any way,
obviously there is some advantage to it.

Is it easier to amplify ? does it amplify better ? Or is it nothing
to do with amplifying it better but that its much smaller ?

There must be some point to it that i don't see.

**broken link removed**
This explains some of the complexities and none of the reasons.

PLL's can be used for many different purposes, what particular application are you struggling with?.