Russian rod pentode circuits

[Murphyv310]

Hi.
Many of us are experimenting with these valves. Michael has been a great source of information as has many forums and experimenters.
What I can't find unless I'm looking in the wrong areas or due to Russian/Soviet secrecy is the lack of original circuits using these valves.
like I say I can't find anything. Do they exist or should I drop a letter to Mr Putin?

[Refugee]

I have a feeling that there will be very few original circuits apart from air craft instruments using these valves.
I wonder if they found out how to male a little chopper circuit to heat a cathode follower?

[Mike Watterson]

There is the Sputnik circuit. I think tt used 1j17b for signals and for PA a push pull class B using earlier version of the high power 1p24b
There was a USSR forestry two way radio, the only non-military set.

I'll look to see what Russian schematics I have.  You need to search in Russian!

There is oddly one NASA circuit! An ultra high impedance battery powered voltmeter.

They work in any "SG" RF, pentode, or triode (tie g2 to anode and g3 to f-, f+ or 0V etc) filament valve circuit.
Unless you have a floating supply or a bifilar wound transformer you can't use input or output at the filament (=cathode).

At RF it's common for grounded grid to fed f- and f+ via a 1:1 transformer as a common mode choke. The DC cancels (f- to 0V and f+ to battery) but it is like a choke to signal, the f- and f+ both coupled to signal via capacitors.

That's ALSO how how you do DL94 etc as audio out "cathode follower" the filament power is via 1:1 transformer, connected so DC currents cancel.

There is no good reason for such a circuit as you need a couple of 1p24b in parallel (that would be 450mA @ 1.2V or 225mA @ 2.4V) and you'd need maybe 150V HT and barely drive 64 Ohms speaker. Far more sense to put transformer wired normally on Anode, and 2 x 1j29b in push pull will give about 2W to 4W! Filament current is less than 1/2 a pair of 1p24b.

A pair of 1j24b is about 25mA filament @ 1.2V (total) and an ordinary small mains transformer will work as the DC bias cancels. Over 250mW at 70V HT.

There are some of the circuits of the military sets that used these on the Internet and the radio museum. But they work (with suitable modified g2 arrangements) in any filamentary circuit from 1922 to 1962, as triodes, replace SG RF tubes (just wire as pentode!) or pentodes. The 1j37b can replace a gammatron.

They are though sharp cut off (apart from odd circuits for 1jxxa dual grid types), serious AGC needs an amp and drive to g2. Also a single resistor can work badly to set g2, you need a potential divider or tap on HT (the USSR sets used both approaches).
Many of the USSR military sets used a pair of germanium power transistors and transformer with taps and rectifiers to give 50V, 90V, 150V etc.

Filament comparisons:
(The 1j42a is similar to 1j24b)
   

[Murphyv310]

Thanks for the info Michael.
My next project will be an FM portable hybrid radio.
I intend to use a TBA820 as an audio output as using the rod valves I'll need more of them for a start and lots of batteries. This would defeat the purpose of the set as it needs to be as compact as possible, light, sensitive, drift free and economic on battery power.
Quite a task TBH but some experiments so far have been successful. I intend to have it crystal controlled with one or possibly two crystals for two stations/frequencies max.
Over the years I've bought countless FM portables for the wife and they either use too many batteries, (rechargeables are short lived before recharge and don't last these days) have poor sensitivity or non PLL sets drift. My wife uses a portable every week day on her rounds and I'm forever fitting batteries.
The idea of one AA driving the filaments and a PP3 for the TBA820 and the dual control filament rod valves sounds good, If necessary half a dozen or more CR2025 could be used for HT, this wouldn't add much weight and the low consumption should give them a long life.
The actual valves I'd use hasn't been marked in stone yet and I'm open to ideas.

[Mike Watterson]

Look at the Vidor Vanguard FM/AM set as it's all DF97s apart from the audio. But use the Philips LD480 and similar for the VHF front end. The Vanguard uses the VHF Mixer/Osc as AM Local Osc, and then the 1st DF97 10.7MHz IF amp becomes AM RF in/Mixer (No DK96).

You need two rod tubes to simulate a DK91/DK92/DK96. One is triodised as Osc. It feeds g2 as mixer LO in on a second rod pentode. Iv'e wired this on a B7G base and verified it works in a DK96 radio set.

The CR2025 can't safely supply much current, with no audio stages (only adds two valves, use 3 x 1N60 for FM and AM detectors) you'd need two stacks paralleled. Using 20 coins per stack. Less will be very poor. Four stacks in parallel will add enough for output stage and then it fits in a B101 box. Though a custom battery pack with a 50V approx tap to feed all the g2 connections is more stable and less waste than other methods.

If you want "hybrid" and small, then use only 1j42a as they can run from the same 9V (say 6 x AAA) as the Audio amp. Though I don't know how well the 1j42a work at VHF.
The 1j24b and 1j29b will work as a VHF Self Osc Mixer, identical to DC90 in the early Philips sets. I've verifiied that the DF97 is always wired as a triode for VHF mixer/osc and they are actually interchangeable without noticeable shift in VHF tuning.

You need a balanced RF coupling (see Philips circuits) on input, otherwise your VHF aerial will massively radiate LO, as unlike mains sets there is never a buffer amp in front of mixer Osc on VHF. USA sets commonly added 1T4 /DF91 or similar in front of DK9x to stop LO radiation even on MW only models. UK sets only bothered on high end models with Shortwave.

There was only one USA portable VHF tube set, a poor one tube regenerative set, though FM was on Band 1 in 1930s to 1945 and Band II from 1945-1946, because it was sold as HiFi and only on mains console / table / radiograms.

Netherlands, Denmark, Germany and Austria had the best ranges of pre 1960s tube VHF/AM portable radios.

I'd not try copying the Sky Emperor. That reflexes the 1st FM IF as audio phase splitter for push pull.
A good few Schuab Lorentz are dual conversion on VHF. Most VHF sets switch off the DK96 (though the Philips Colette* runs it on Gram and VHF to provide negative bias for output push pull!). The Schuab 1st IF is 10.7MHz. Then the DK96 adds gain by conversion to 6.5MHz for the rest of the IF amps (shared with AM IFTs).

(*Curiously the grid of LO goes up to 9V negative, so no diode needed, just a low pass filter of 2 x 1M or 2M (I forget which) decoupled twice to grids of the output DL96 push pull. The Colette uses the DM70 purely as power indicator and -1 gain phase splitter even though it *DOES* have a second DAF96. The second DAF96 is purely an active tone control! Swapping a couple of wires makes the DM70 /DM71 display AGC level and used the tone control amp as phase splitter. I can't figure why Philips did that. Mod reversible in less than 10 minutes!)

[Mike Watterson]

Valves:
Entirely 1j24b and 78V - 80V HT from CR2032 (parallel stacks with 1N4148), or safer use PP9.
OR
Hybrid set using maybe 1 off 1j24b for VHF mixer/osc if 1j42a doesn't work. Otherwise all 1j42a. Use TBA820 or 8 pin stereo head phone amp (they are not just SMD, 8 pin DIL are on eBay) in bridge.
Investigate safer A23 or similar 12V batteries (about size of N / Lady cell) in series and parallel with 1N4148, stacks of CR2032 are dangerous, though nice fit for a B101.
Note, don't operate 1j42a above 9V!
If using alkaline batteries for filament rather than NiMH, then put 39 or 43 ohms in each f- lead, (1j42a or 1j24b). They are designed for Silver Zinc and NiCd power.

You'd use 1j29b as front end RF preamp and a pair in push pull for audio out on a high performance set with Shortwave.
The 1j29b in Push Pull will also do RF transmit up to nearly 3W peak (SSB).
The 1p24b are shorter life high power (hence 220mA parallel, 110mA serial) for radar in proximity fuses up to 200W peak! You can run them about 16W to 20W total power out as a pair in class B push pull RF. Perhaps 10W reliably class AB at good quality audio.

[BusyBee]

Not sure whether this is known but it answers partly an original question - see this link for schematics (see Russian radio section).

The R-326 is a good circuit to look at. I also have R-126 but on this site the link does comes up with an error.

[Murphyv310]

Hi BusyBee.
Nice to see you here and thanks for your post.
Unfortunately I don't see the link. Can you repost it please.
Many thanks.

[BusyBee]

Sorry, but it may have been my unfamiliarity with the forum (not helped by the fact that I did not instantly see the post).

This is the link: http://www.cqham.ru/sch_eng.html

(cqham.ru/sch_eng.html if the link does not copy)

I have just checked and now the R126 link does work

[Murphyv310]

Brilliant.
Thank you very much.