Simple micro transmitter

[Murphyv310]

Hi.
Since I made this up I have made some changes.
The triode AF amp has been replaced with a Pentode 1Ж18Б. The original only gave marginal gain and on low level sources didn't give enough audio.
The HT for the 1Ж18Б is derived from a small inverter that gives 70v, the anode is fed via a 100k and the G2 via a 2.2m resistor. Bias is derived as in the last circuit.
I cannibalised a strange Christmas light that is some sort of plasma device and I use the inverter to feed the RF amp and input audio amp. So far it works perfectly.
My plan is to rebuild this and move away from the laminate sheet and finalise it properly.
I have proved it's reliability as excellent so time to tidy it up and sign it off as comlete.

[Murphyv310]

Hi.
Just a quick update. I've run a thin cable around the roof space of the shed all the way round. I've removed the PA stage and made a 10:1 RF transformer with a toroid with the primary connected to the dual valve anode to 9v HT. This gives excellent signal to all the sets in the shed. This works by far the best for me. The ends of the cable are connected to the secondary of the toroid and are not connected to any other point on the circuit, this has removed all traces of modulation hum.

[BusyBee]

That sounds good! It may be useful as a 'picture rail' aerial for receivers too?

Tracy

[Murphyv310]

Hi.
Latest modification to the single valve transmitter.
Short wave........... https://youtu.be/7RcNJVhxELo

[Murphyv310]

Hi.
Here is the circuit I'm using for a shortwave pantry TX.
Virtually any valve radio audio output transformer will do. Even a little MP3 player gives enough drive, remember this circuit is flea power but it works very well on short wave. Some experimentation will be needed for the tuning coil.
Aim for 1.1 volts on the valve filament. B2 a PP3 should last for a very long time, I use a rechargeable.
The 1J42a oscillates happily up to 18mhz and could well go more but 18mhz is the highest xtal I have.

[Kalee20]

Thanks!

Basically a modulated oscillator, electron-coupled to aerial.

Good report - I'll hopefully copy your design!