Russian rod pentode circuits

[Murphyv310]

Hi
Well I'd really like to obtain a couple more 1j42a if humanity possible, thing is I've seen none anywhere for years.

[BusyBee]

1j42a's are something which I look for occasionally but I have not seen any at all since I first looked. Obviously the Russian supply is minimal at the moment but I do have the feeling that the supply of rod pentodes, in general, has dwindled in recent times. The prices have gone up too (Russian made valves in general). The common rod pentodes which we use seem to be reasonably available though. I bought a few more 1j37b's a while back as I see them as something I will use. How efficient in comparison I know not but I like them for mixers and have done a bit of experimenting with audio.

Tracy

[Mike Watterson]

The 1j37b seems like an older type and very simple and inefficient*. It needs a centre-tapped RF transformer between g1a and g1b for best performance as mixer. Differential signal is usually LO and common mode (RF to centre-tap) is input RF signal. Mostly they were used as low level gain/attenuator blocks at RF, IF or AF by feeding signal via caps to g1a and g1b, but variable DC on one g1 and fixed bias (such as 0V) on the other grid, then increasing or decreasing the DC volts above or below zero will vary the gain. The 1j24b is only 10 or 11mA filament and the 1j37b is about 56 to 59 mA filament.

The 1j37b can be used as a gammatron, but that's more a curiosity than efficient.

The advantage of a 1j42a is that you can run two filaments in series off one NiMH (0.5V to 0.65V each) and use a single PP3 for HT with a ceramic earpiece to make a two valve regenerative radio.
I was thinking of a small superhet using one 1j42a as mixer (one as LO to g2), two as IF (because gain low), 1N60 detector (predates early rod pentodes by nearly 5 years) and 1j24b for speaker. About 32 mA filament total (as the 4 x 1j42a in series/parallel), 9V and 45V HT. I'd try it with transistor IFTs and I know a sub-miniature Clock Radio mains transformer works to drive 8, 16, 32 or 64 Ohm speaker depending on HT.

I'll offer my 1j42a valves here if I don't do it.

[*A Russian doc translated by a Russian who became Ukrainian has
There were basically three main stages of rod tube development.

1К12Б, 1Ж17Б, 1Ж18Б, 1П5Б, 2П5Б - original Mid 1950s
1Ж24Б , 1Ж29Б, 1П22Б, 1П24Б improved
1Ж37Б, 1Ж42А, 1П32Б extended use.

Lifetime is in excess of 5,000 hours. Much longer with stable filament.
from https://www.radiomuseum.org/forum/summar...todes.html ]

[Murphyv310]

That's a kind offer Michael of the 1j42 valves if you don't make it. I'd certainly give you what you want for a couple (within reason of course).
Would even be happy to make your project too.

[Mike Watterson]

We should also try some QSOs when I get up aerials!

[Murphyv310]

We should also try some QSOs when I get up aerials!

I'm certainly up for that Michael