Russian rod pentode circuits

[Murphyv310]

I like that, really neat.
I know loops and frame aerials work as a transmitting medium and if you get the range you want it is a very tidy solution.
I'd really like to see your circuit if possible.

[BusyBee]

Thanks Trev

After I quick test this evening, I think range may be Ok, but it may be a case of a closer look at depth of modulation depth. The signal strength is Ok but audio seems low. It is not helped by having little control of input. I have an audio pre-amplifier on my things to build, and it may well be the time. It was not helped tonight though by the flood of stations due to the propogation conditions.

No problem with seeing the circuit. That was always my intention, and I need to have a closer look myself as currently things are a set of sparse sketches. I may well be overlooking some things myself (almost certainly). It will take me a week or so to put things together, but will post when I have them.

[BusyBee]

When I checked on coupling tuned circuits I determined that I had probably got nearabouts optimum coupling for RF output. Somewhat lucky as I was only putting a small value in to avoid loading issues. I have now done further tests and found the radio to be stable. Range seems to be as required, covering the house fairly well and dying away at boundaries. Further tests will be required to verify.

I have found, as previously mentioned, that modulation depth may be the tricky part. Reproduction seems good, but with high modulation (overmodulated) audio is harsh. It is possible to see reasonable modulation on the scope, even with music output, but such monitoring is really impractical for portable operation. At present I have used a preamplifier fed by my Sony disc player, this pre-amplifier being a speech processing circuit for Tx use which I constructed from an article in ham book many years ago (when I mostly just constructed rather than designed things). A suitable amplifier with output monitoring may well be a useful addition. I will think and research. In fact now is the time to reflect!

I have now managed to write things up a bit - shown here. The notes are really as a reminder to me.

Anyone looking in should note that this, although looking complete, is really a bit experimental, and a prototype rather than something to be copied as a working item (although it does work and seems very stable). Mainly a colletion of ideas!

[Murphyv310]

Hi.
I did this video some months ago but it shows the two valve version working with some scope traces. https://youtu.be/h3xKNB9e5XQ

[BusyBee]

It's an interesting video (as all yours are). Something I am not really geared up to do although I probably have the technology with a little thinking.

I like to see different approaches achieving a similar result. I don't have any 1j42a's but in some ways it is better as, although I like to work on lower voltages, in many ways very low voltage brings additional restrictions / limitations. It is useful to see your approach as, although my circuitry has little issue on MW, higher frequencies would be difficult and for VHF techniques would have to be different for me. The thought had crossed my mind to try a VHF converter down to the range of my comms receiver. That would be a dab of the toe to test higher frequency capabilities of these valves.

I get so many ideas - just gets down to time

[Murphyv310]

Hi.
I've managed over 100Mhz. At one point I was going to make a fixed frequency FM receiver that was hybrid Rod Pentode with chip audio. Got it partially working but the batteries were an issue as it was intended to be a pocket radio.
Now abandoned.

[Nick]

Lovely job - most impressive. Nice video too...

[BusyBee]

think it's about time for an update. I have been busily working away and made a little progress.

The only real thing I have done with my pantry transmitter is dyed and polished the outside of the box as shown in the photo. From the outside it perhaps only looks like an antique box now as there are no external controls. I did a little work on nonitoring modulation depth etc and found a few old circuits, with a view to updating. On close examination though, they did have limitations (mainly, I think, due to them being designed for use with higher power equipment). I am still thinking on that one.

I had thoughts about increasing the frequency of operation, and did think about making a VHF convertor. Initially I re-designed one of my 1J29b modules as a 20MHz crystal oscillator. My intention to drive a 1J29b frequency multiplier stage up to 80MHz. The 20MHz oscillator worked, although tuning was critical (peaky). After this was set, it worked well. My efforts to create the 80MHz tuned stage though came to nothing. I think mainly due to tuned circuit issues and my limited experience at that frequency. I was not helped by the fact that my dip oscillator seems to have a flat spot between 50 and 100MHz.

Some time back I bought a 50MHz oscillator module. It seemed a good idea to use this to feed a 50MHz signal into my multiplier, just using it as a fundamental amplifier for test purposes. With this in mind I added a two transistor buffer (straight from ham radio book, but with change of transistor) to the module (see photo). I constructed a new coil for the 1J29b amplifier using tinned copper wire, with intention of lower Q so easier tuning, but with sleeving to avoid shorted turns. On test this worked without problem (see photo of test setup).

From this, I then reverted to my 20MHz oscillator module. This now worked on the 2nd harmonic (40MHz) and the 3rd (60MHz)(maybe at the limits of tuning). I think I could go from this to my original 80MHz, but have, in the meantime, lost my drive for the convertor, so maybe won't. I have far more interest in HF, and the results indicate to me that I should not have major problems there.

During the last two months I have designed and constructed a new power supply unit. This provides HT, heater and bias supplies, plus a further positive supply. These are provided via four separate transformers so individually isolated from each other. The purpose of this is a utility PSU for lower voltage valves (both Russian and western), plus 5V digital IC's and transistors. This, I was also able to test (see test rig photo – the top connected box).

One problem I have realised in my tests is that I have poor test equipment for VHF. My scope is 50MHz and, although I have tested it with signal up to 100MHz, at which time sync appears to fail, it is obviously on its last gasp (my waveforms shown here are using X x 5 option to show clearly at minimum time [50nS]). My dip meter is useful. But has it's limitations. I have started to look at my SDR. It looks like it may be useful but I'm not sure how much. Testing with the 50MHz oscillator plus amp (with SDR in an adjacent room), signal was received, but I suspect the input was being overloaded as the harmonics content seemed too high. If anyone has used these for test and has any initial advice (or links to) I would appreciate it. (See photos). Not intending extensive work at VHF and higher I don't intend to accumulate a lot of additional test equipment.

As can be seen from the photos- I have created a higher frequency version of my rod tube module for VHF use. This is my first attempt, and does seem to work. Unlike at lower frequencies, I cannot be certain how well as I am using a pickup loop on my scope rather than probe. The main design aim of the module was to separate input and output circuits. The DC components are relatively unchanged. The circuit design of these modules (at least those described in this post) follow normal design, not using any special quirks etc of these valves. By and large I find the module approach useful, particularly with these Russian tubes.
                               

[Murphyv310]

Great work indeed.
Glad there are a good few experimenting with these wonderful devices.
Looking at your work just be careful you don't land up with a time warp and get transported to a Russian valve factory.
Have fun.

[Murphyv310]

Hi.
Well for some time I've been trying some circuits using Super Regeneration. My main idea has been to make a simple FM set and of course I intended at one point was to make a fixed frequency portable for Anne.
Using a 1Ж18Б I found it possible to make a Super Regen but in no way could I coax it to work up at 88mHz or above. I actually got success on the 11 meter CB band and heard a couple of times NBFM from no doubt a local CB station, fairly loud into a pair of headphones with virtually no aerial and just one valve.
Next I tried a 1Ж24Б, with this valve I got very weak results on 89.5mHz BBC R2 but at least it did work to an extent, higher frequency stations didn't come through.
I then though that the 1Ж29Б might be a better bet. All of these little tests were made on double sided laminate board for screening and stability. I have had really good success with the 1Ж29Б all the way up though Band 2 and with a small change to the tuning coil I could receive Prestwick control tower. Take mind I'm not using an external aerial. On FM, volume from one valve is perfectly loud enough on a set of high impedance phones.
The circuit is very simple. I have wired the filaments in series with the centre tap grounded, the Super Regen oscillator coil is 25 turns of litz wire wound round a 1 meg 1 watt resistor and the tuning coil is 4 turns of 14 gauge enamelled copper wire across a beehive trimmer for the tests.
I'll pop up a circuit later.