Simple micro transmitter

[Murphyv310]

Important to understand that the g1a and g1b are not like two gates on a FET. It's the same pair of grid plates that pinch the electron beams as on all the other rod tubes, but not tied together.
Thus if the signal is common mode, the characteristic (gain etc) is identical to a regular rod tube. Unless you have a modulator, special AGC, frequency doubler, detector or demodulator, tie g1a and g1b together.

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.

1j42a and high power 1j37b
Frequency Doubler and Detector operation
The differential voltage  is like the voltage on electrostatic deflection plates of a CRT. Actually the tube is totally Electrostatic. G2 and G3 are an Electron lens. Thus no matter what the beam current is from the regular common mode (g1a and g1b portion that matches), the differential voltage deflects the beam onto the g2 rods and g3 rods (or plates, the 1j37b has rods for g2 and g3, two for each on each beam = 8 rods, the pair of anodes are plates. The 1j42a has a slot for g2 or g3, I forget which, and a triangular  pair of anodes). So the current on Anode drops and current on g2 & g3 rises, no matter which polarity the g1a and g1b difference is. So the main signal that is the same on g1a and g2a will be varied in gain. If there is no common mode signal, then actually the differential signal is full wave rectified. If you put a high pass filter, it's a frequency doubler, and if you put a low pass filter, it's a very good detector, sensitive and full wave!

As yet any experiments using the 1j42A as a FW detector have been fruitless, poor performance and with severe clipping

Mixer Operation

You use a centre tapped transformer for the LO drive. Only low level is needed. the + and - phase drive the g1a and g1b. The RF in or Audio in (or IF in if it's part of a BFO detector) feeds between 0V and the centre tap, so both grids are fed equally. The other way of using a Rod pentode as a mixer is to to direct couple a triodised (g3 to f-) Rod Pentode oscillator anode to g2 of the RF amp/Mixer. No other bias needed. This might be preferable for RF in as the LO leakage is less, even though a higher level. A separate Osc and Mixer is always preferable to single valve solution (Hexode - Triode ECH series better than EK or EH etc Octodes, Heptodes, Nonodes. There is actually Triode Hexode and Triode Pentode 1.4V battery types as well as 2V types)

A centre tapped TX cant work as it will be in antiphase to each grid thus cancelling out, so this project cannot work like that,
I'd suggest you build the single valve modulator and report back.
I'm somewhat disappointed at your comments after proving this very simple TX works.


May I also reiterate that these valves do not behave like what we are used to. The use of lowish value grid resistors increase distortion, all the curves in the world wont change how they behave in practical circuits.