Russian rod pentode circuits

[Murphyv310]

Hi.
Have now done a video. Not my best and it shows the shortcomings of this type of circuitry. Nevertheless better than watching soaps !!!!
https://youtu.be/toCOwQaBqL0

[Murphyv310]

Since the video I've reverted back to phones. I've added a two turn aerial coupling coil placed 6mm in line with the RF tuning coil, one end grounded and the other via a 11pf cap to the centre of a coax socket that has been soldered to the tin can. Connecting it to my FM three element aerial is a revelation, good strong audio now and its pulling in very well with good separation. I'll fit a phono socket for low level audio and connection of the phones so the lid can be fitted to the box, an on off switch may be useful too.
I added some crude stabilisation to the inverter with two 57v zeners across the HT so I'm running 114v HT, no apparent issues with the 1j29b. I may add a second valve and small transformer to drive more modern, low impedance and comfortable headphones, those old ones are sore on the lugs.

[Murphyv310]

Hi.
I've replaced L3 from a 10uh to a 10mh for the HFC, also removed the 1nf filter cap, this has made a big difference, the rumbling noise has virtually dissapeared and headphone drive is now too loud but also a less distorted audio with better top end.
I think I will redo the video as the improvement is very much marked.
I've also tested for interference using another radio and its only a few feet.

[BusyBee]

I have just watched your video Trevor. It is inspiring me to put together a circuit. I find it easy to get sidetracked lol. I have ideas on a superhet, but, as usual, I am getting far more involved and the (as yet not to paper) design is sprawling a bit. I love to see your approach.

Tracy

[BusyBee]

Hi everyone,

I have been doing other things, with various Russian valves. I did a little with a regenerative receiver with a rod pentode after being inspired by Trevor. I need to tidy it at some point, but have received a couple of stations with a lashup (Medium Wave).

My interest with radio is more toward a superhet though. Elsewhere I did come across someone suggesting using a Franklin oscillator, which looked interesting. I put together a test circuit using an ECC82 (easily done as my (homebrew) valve test equipment is modular). I got the shown skeleton circuit to work, (details in attached working sketch). Then I progressed to an 6N16b. This is a Russian miniature double triode. Each section seems identical, and cannot easily be determined as far as I can see as there is only a diagonal in the glass base to indicate pin location. This works similarly with both sections. In a similar manner to someone online who has used an IC socket for these I soldered direct as per the sub-diagram on my sketch. I had previously tried making a module using the 6N16b the same as with my rod pentodes, but got hopelessly confused with connections. The IC socket type layout works well for me and seems tidy (see attached photo). I didn't use a socket as I am not sure of reliability with wired connections. The circuit in the photo is intended for a local oscillator for use with a MW superhet (with and addition tuning capacitor). This, I have just used for testing at the moment, but I got tracking over the correct range for 455 Khz IF (just the oscillator, no RF circuitry). I plan to continue with this at some point.

Now to the point – I decided to try using two 1J24b's in a Franklin circuit. I made a new module using two of these (see photo). I did have a few issues, I think due to the low gain of the 1J24b's. I have noticed this before, and have used 1J29b's in other circuits with better results. I did find that, in using this type of circuit with a double valve board, I had g1 connection issues, using long wiring runs. This, I think, added additional capacitance etc and tuning was a bit out. The circuit, as made, works reliably, but only to a bit over 1MHz. It was stable, but I think (especially in comparison with the 6N16b or even ECC82 which I found work much better in this circuit), I will not continue at this point as I can see redesign of things would really be required and I have other fish to fry.

On another point, I have been thinking of an amplifier specifically to feed my record deck into my Pantry Tx. I had the thought of using a 1J37b as a mixer, feeding each channel into a seperate grid.
As yet it is in early stages, but one thing relevant I found is that the gain from each g1 (the other being grounded) does not seem to be half of the combined total (both grids driven), as found by Joe Sousa (Radiomuseum). For RF it may be of less relevance, but for an audio mixer it would be more important. I have not done formal testing, but on more than one of these tubes I have found a difference. I would suggest that anyone intending using one of these valves in a critical application check. This afternoon I set up a circuit to vary the bias hence vary gain. I got a rough balance when g1a was biased to -1.5V, and g1b at Ov (ground).

Tracy

[BusyBee]

Just a minor update on rod pentode circuits for those interested.

I am in the process of working on my TRF radio, but broke off to order some new valves so went back to my pantry Tx as I had never really got the record deck into it. (see last post). I have now tried the 1j37b mixer technique and found that it does work. I used my audio processing circuit, mentioned previously, which I made from the RSGB VHF UHF Handbook many years ago, putting these with a PSU in a case. I have to say that, although the system works, modulation depth cannot be raised anywhere high enough using the deck for optimum reproduction. I can see some reasons why not, but I think using old modules in less than ideal arrangements bring bigger problems than a new, clean design, would. I will give it further thought. Trying to design around a specific circuit, particularly not having the original designers notes, is not easy.

One side result of this though was my organisation of negative grid bias. I used a couple of capacitors from the AC 12V input to the PSU (I used a strange wall wart having seperate 12 and 24V AC out) to a seperate bridge to provide a negative supply. Then using a regulator and trimmer pots I obtained the needed adjustable bias. Thinking further, I thought about Trevor's work on rod tubes with isolated heater power. This would perhaps be an easy way of providing any number of isolated heater supplies.

Tracy

[Murphyv310]

Hi.
I see on the UKVRRR forum someone is asking if a Millar Transitron oscillator will work with a rod pentode. It certainly works with the 1J29b and should with the others that have separate G2 & G3..
Maybe someone could put a link to this post or thread on there please.

[BusyBee]

A bit of a change with this post. I thought I would put it here as it does include a Russian Rod tube as well as  a regular Russian miniature tube.

I have been thinking about interfacing valve circuits with transistor. Particularly a transistor audio output stage as that would easily avoid the use of an expensive output transformer, usually used with valve circuitry, transformerless output being tricky. The issue here is often matching the higher impedance output to lower input impedance of transistor stages.

Thinking reverse engineering with a difference I remembered an interesting circuit in my Fet Applications Handbook (see photos). This appears to sort impedance matching issues.

This circuit uses a fet input and transistor output. The design aims in the article (that I can more readily test and aim for) are a gain of 60 +/- 30%, O/P imp < 1.5kOhm, 1V O/P PtoP (1% distortion), with a supply of 45V.

My plan was to design a circuit using a 6j1b miniature pentode in place of the fet in one circuit. I also modified an existing circuit which used a 1j24b rod pentode to give the same result. For the valve circuits I planned to increase the supply voltage to 60V and use a (higher voltage) BC546 as the transistor.

I planned to use a 10kOhm resistor as load (to be much greater than output impedance) for testing gain. Input was sinewave at 1kHz. The article states bandwidth design, but I generally followed and did not test for at this point), Output impedance, although not easily tested without good equipment, I would likely get a reasonable approximation by lowering the load until the output wave form was reduce by half (not totally sure but it seemed to get figures in the right area – please let me know if that is a false assumption).  I cannot easily test the distortion figure but looked for minute changes in the output waveform as the limit when measuring input and output limits. I did find lowering the output load resulted in distortion in the waveform so had to reduce the input level to a point where this did not occur. All signal voltages are P to P.

The designed circuits are shown in the photos.

With the 1j24b the results were gain 46 (input 100mV), output imp 650 Ohm (approx with I/P 50mV), max output level 14V (between 250 and 300mV I/P  – exact figure difficult to measure) and current consumption 950uA.

With the 6j1b  the results were gain 48 (input 100mV), Output imp < 500 Ohm (with input 50mV), max output level 14V (between 250 and 300mV input – exact figure difficult to measure) and current consumption 1.4mA.

I will say that perhaps the biggest thing to come out of this was that my test equipment is rather limited, but I am pleased that my results, in their limited subset of the original article specs, seem to come well into the range planned in the article perhaps apart from the supply current which is slightly over, but acceptable. This bodes well for future possible replacement of fets by valves (rather than the usual other way round) in the future. I plan to go further with these modules and see how useful they are.

Tracy

Tracy                    

[BusyBee]

Hi

I have just found this manual online which provides information in English on Russian valves and transistors etc (including rod tubes). I have not seen it anywhere before so thought it worth a mention.

https://nvlpubs.nist.gov/nistpubs/Legacy...ote715.pdf


Tracy

[Refugee]

That is a useful book for USSR parts. I have saved a copy.