Simple micro transmitter

[Murphyv310]

Hi Terry.
Luckily I have about three or four 9Khz dividable crystals in my junk box, a lot came from Jeffrey which may have included these. There is a little interference at night especially if the tank isn't set up properly but at the power the circuit uses it must be remembered that the output is at flea level  
To my mind this is ideal as it will never be a problem for neighbours etc.
I might do a second You-tube video today, assuming I don't get a lot of jobs from SWMBO

[Mark Hennessy]

Hi Michael.
I'm not so sure if you're comments really are helping in this project, are you implying this wont work?? Looking at the spec there is no reason to say it wont plus I have proof it does and that my friend is the ultimate end I've done.

I'm somewhat disappointed at your comments after proving this very simple TX works.

Come on Trev - no need to be defensive. I've read Michael's posts carefully - they contain interesting theory about the rod pentodes, but no criticism of your project.

Like many, I've enjoyed reading this and seeing/hearing the results. Ignoring the preamp, it's amazing what can be done with just one active device! Keep up the good work

Mark

[Murphyv310]

Come on Trev - no need to be defensive. I've read Michael's posts carefully - they contain interesting theory about the rod pentodes, but no criticism of your project.

Like many, I've enjoyed reading this and seeing/hearing the results. Ignoring the preamp, it's amazing what can be done with just one active device! Keep up the good work

Mark

Hi Mark.
Sorry if I came across as defensive, Michaels posts have always been helpful and have spurred me on with the rod valves, two comments though come across as this doesn't work. The proof of the pudding though is in the eating as they say, anyway lets not let it get in the way of this little project.

I've done a second video (cut off at the end though) this one with the pre amp, I'd say the third valve is unnecessary, the gains are small and frankly not really worth the effort.
Since the video I have changed the tank coil, it has upped the range outside from the shed to 25 meters and improved reception in the house no end.
I'll do a little video tomorrow with me taking a portable radio round the garden to give an idea of usable signal levels.
My video's have no airs an graces, you get real life rubbish videos I'm afraid, sad I was born with two hands not three

https://youtu.be/h3xKNB9e5XQ

Oh and thanks for the encouragement Mark

[Murphyv310]

Hi.
Michael mentioned about bringing a magnet close to the valves. Now this is really fun. Bringing a magnet close to the modulator cuts off oscillation dead, bring the magnet close to the audio preamp and the gain rises slightly then as you get closer again the valve gets cut off.
Now this makes me wonder how much use would these valves have been in an EMP or nuclear EMP, the whole idea of the Russian's using thermionic devices was for that very reason.

I wonder now if it is possible to do some electromagnetic coupling on these valves too? All very interesting and a great learning curve.

[pwdrive]

Drop a speech coil over it and give it some wellie?

Lawrence.

[Mark Hennessy]

That's working really well now

The envelope looked very nice on the 'scope screen. I thought I could hear a fair bit of 3rd harmonic when you played the tone, but there are so many other things that could be causing that. I must say that it sounds really quite good with the music...

I wonder if a coil wound around one of those would allow much gain change? Thinking you might be able to do AGC or similar. That said, I imagine the coil might end up needing more current that would be ideal for battery use, but you never know.

Good stuff

[Pat Pending]

Now this makes me wonder how much use would these valves have been in an EMP or nuclear EMP, the whole idea of the Russian's using thermionic devices was for that very reason.

Hi Trevor, after the EMP has passed the valve
would still work, your transistorised gear however would likely be toast. Some of the miniature valves are also very photosensitive I've found.
Super project Trevor, BTW.

Cheers, 
Andy.

[Mike Watterson]

Hi Michael.
I'm not so sure if you're comments really are helping in this project, are you implying this wont work?? Looking at the spec there is no reason to say it wont plus I have proof it does and that my friend is the ultimate end I've done.

I'm somewhat disappointed at your comments after proving this very simple TX works.

Come on Trev - no need to be defensive. I've read Michael's posts carefully - they contain interesting theory about the rod pentodes, but no criticism of your project.

Like many, I've enjoyed reading this and seeing/hearing the results. Ignoring the preamp, it's amazing what can be done with just one active device! Keep up the good work

Mark

@Trevor No criticism intended at all.
I'm only explaining why the dual grid is NOTHING like a differential amplifier (almost the opposite!) and NOTHING like how a dual gate FET works. Unlike every other device, the g1a and g1b is a split connection to the normal TWO grid plates in any rod pentode.

I'm repeating the theory from the Russian data, translated Russian articles (by Demetri) and added to by Joe Sousa's tests and disassembly. Joe is extremely expert.

In practice almost any circuit works (even unlikely ones) as oscillator, amp or mixer with rod pentodes. You can even inject modulation at g3 or anode, especially with the regular types using only 15V to 22V HT.

However understanding the theory allows optimisation of the circuits and good & reliable performance.

Top view of the two beams. Applies to 1j17b, 1j18b, 1j24b, 1j37b and 1j42. The 1j29b and 1p22b and 1p24b have a second filament and parallel pair of beams.
   
   
On the 1j17b, 1j18b, 1j24b, 1j29b, 1p22b and 1p24b the g1 plates are all internally connected.
On the 1j42a and 1j37b the two g1 plates either side of the filament are separate, g1a and g1b. So if g1a is tied to g1b the 1j37b is similar to a 1j18b and the 1j42a is similar to a 1j24b, but lower HT due to closer spacing of g2, g3 and anode. There is another unusual feature of the 1j42a as unlike 1j37 it's more customised (the 1j37b is a simplified 1j18b and has even less screening!)

General construction:
   

1j37b (high power version of 1j42a) top view
   


Push Pull TX (1p24b), 220mA @ 2.4V, 440mA @ 1.2V
Russian circuit, portable military
   
Triodised this can do 1.6kW peak for radar in a proximity detector of a shell etc, (shorter life!)

More shortly...

[Murphyv310]

Thanks Michael.
I certainly agree these valves really don't do what you'd expect.

Yes Mark there is a bit of 3rd harmonics, that seems to be from the preamp TBH and this doesn't happen with the single valve TX or with the three valve set up with feedback, backing off the gain on the two valve TX does reduce third harmonic distortion.

Back to Michael.
I've tried using the other rod valves as a Micro TX and yes these work well to and are easy to modulate, you need a higher HT which gives more range of course but my idea on this was to get as low a component count as possible.

Pat
Of course you are correct about the EMP, the valves will be fully functional after the pulse.
Incidentally, I'd love to see all enthusiasts using these wonderful devices and if my little circuit gives pleasure elsewhere then please go for it.

Many thanks for all that have looked, to Michael for getting me started with these valves and J Sousa too for so much info

[Murphyv310]

Drop a speech coil over it and give it some wellie?

Lawrence.

Now that could be an idea