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Old 26th Jul 2011, 10:35 am   #101
dominicbeesley
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Default Re: Russian Military Subminature "pencil" valves

Hello,

I've got a load more of these and look forward to having a proper play with them. I've got a few 1* ones (1P24B, 1J37B and 1P24B) not sure what I'll make but am considering a portable HF receiver as a first project.

I've also got some 6* ones (6J1B and 6N16B) I'll be using these along with some American valves in my 405 line NTSC colour decoder project. These are more conventional with "proper" grids as opposed to the rods used in the 1V valves.

I also got some SG5B voltage regulator tubes, these are the same size, are Ar/He filled and give about 140V out at 5-10mA. I tried one out last night on 240Vdc with 10k in series and they give a pleasant bright purple glow round the edges though not very bright...they do however get very hot - is this normal?

Dom
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Old 26th Jul 2011, 12:07 pm   #102
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Default Re: Russian Military Subminature "pencil" valves

The 6* series are just miniature ordinary valves. Not good for battery due to typically 1.5W to 2W heaters (6.3V indirect).

I know little about gas regulators, but 10K sounds absolute minimum resistance, that's at the maximum current. 140V x 10mA = 1.4W!

Gas regulators are very noisy and also usually have negative resistance, so I'd always use Zener/Avalanche diodes.
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Old 26th Jul 2011, 10:40 pm   #103
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Default Re: Russian Military Subminature "pencil" valves

This is the most reliable 2 x PP3 + single 1.5V circuit I've managed for the 1j18b

It's a one valve regen/homodyne. The Pot is pretty sharp and so is tuning!

Tested with and Earth and 8' whip and random wire Aerials on LW, MW and SW

2l plastic bottle for LW, about 250 to 300t (360 is too many!) and 100T for feedback.

500ml plastic bottle for MW

loo roll sized plastic tube for SW.
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Old 26th Jul 2011, 11:20 pm   #104
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Default Re: Russian Military Subminature "pencil" valves

With a Pentode rather than Triode operation the advantage is that you don't need an RFC (Radio Frequency choke) on the Anode. The screen grid is essentially acting as a psuedo RF Anode and the actual anode as AF Anode.

Regeneration is essentially "Q" multiplication by using the screen grid for controlled positive feed back to cancel the losses of the coil (which lowers Q). The Q becomes very high just before oscillation. The Pentode characteristics are such that the valve is also a mixer, so at almost oscillation the carrier mixes and creates baseband and twice frequency components (What people called Homodyne/Syncrodyne, though these are regarded as two diffferent modes by some writers). Since the Anode is decoupled at RF (220K and 470pF), only the modulation is left on the anode.

I can only test MW at night as there are no MW stations near. But Five Live and "Absolute Radio" 1215 very clear from Twilight.

R1 RTE 252 LW during day with very faint BBC R4 and slight "growls" on other LW frequencies.

Anyway, no diode detector needed.
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Old 27th Jul 2011, 9:45 am   #105
dominicbeesley
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Default Re: Russian Military Subminature "pencil" valves

I do like that circuit, and a good explanation of what is going on, I have to admit it's just taken me ten minutes of headscratching to work it out before I read your next post....

I'll have to try and skive an hour today to try that one out.

Dom
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Old 27th Jul 2011, 11:01 am   #106
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Default Re: Russian Military Subminature "pencil" valves

Normally there is a series resistor bypassed with capacitor to bias the grid more negative. At the 18V to 22V HT (PP3s sitting on the filament supply) and grid biased to 0.25V below "f-" (the 12 Ohm resistor between -LT and f-) the bias is OK. Adding such a "grid leak" scheme makes it tend to oscillate at low audio frequencies.

Also there are usually a couple of RFCs (Radio frequency chokes) with problems of self resonance. The "reaction" or "tickler" coil feedback is often adjusted with a variable capacitor for historic reasons, now a 50K Ohm pot is much easier to get. A 100K may be a little better.

The Aerial is often coupled via a 3rd winding. If the aerial is very long or 50 Ohms, then a 3rd winding with about 1/3 or 1/4 the number of turns of the "tickler" or feedback winding may be needed. A Short whip is very high impedance and the series coil helps match it and reduce its tendency to affect the tuning. I used a "resistor" sized 1mH coil. You can wind an air core one.

Next to try is a tuned loop so no separate aerial whip is needed. It will have two windings and replace the coils. If the main winding is two parallel windings of 35 turns on about 18" (45cm), I think switching from parallel to series will quadruple the inductance an thus the one loop will work for LW & MW.

The colours are the "standard" large ferrite rod aerial colours. If winding your own make the "tickler" or feedback coil about 1/4 turns of main coil and beside it on ferrite, or on top at "earthy end" on air-cored. If there is silence at all positions of pot, reverse connections on the feedback winding. It should get noisier as pot slider moved from HT resistor. If near a station it will squeal if turned to high. If turned full it will be totally silent again as the circuit simply oscillating. So adjust pot over full travel before deciding the feedback wires need reversed.

1.0V to 1.35V is fine on the filament. These are not like D-series battery valves, which are designed for direct connection to Carbon-Zinc, these are designed for NiCd batteries. Hence 0.9V to 1.4V limits in data sheet. The extra 0.25V across filament resistor really optimises the grid bias at these low HT volts.

Without changing grid bias and the HT resistors, the radio will work no better and likely worse on 45V HT!

Last edited by neon indicator; 27th Jul 2011 at 11:15 am.
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Old 27th Jul 2011, 10:05 pm   #107
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Default Re: Russian Military Subminature "pencil" valves

Some notes on the regen radio in Post 103:

It *does* work 12V to 70V HT just changing R8 from 100K to 270K. At 18V (2 x PP3) it's a bit better with R8 = 56K

Depending on your coil it may be much smoother "ideal detection" point with R9 as 22K pot or even a 10K pot.

Connecting G2 to "blue" / R9 pin 3 point instead of slider and connecting C12 to slider pin 2 of R9 pot instead of pin 1 R9 gives slightly smoother adjustment with a 22K pot.

R7 can be as low as 100K for driving a transistor amp or as high as 390K driving valve amp or crystal earpiece.
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Old 27th Jul 2011, 11:10 pm   #108
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Default Re: Russian Military Subminature "pencil" valves

Three "French" stations tonight on LW (two very very strong) + RTE1 (252) noisy. R4 LW quite weak.

With 390K anode load for R7 you need to reduce C11 to 100pF or even 10pF or you won't have much treble!
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Old 28th Jul 2011, 8:50 am   #109
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Default Re: Russian Military Subminature "pencil" valves

Revised Schematic (works best at 2 x PP3 with default values). Included is optional 3 valve audio amp using a 5V or 3V 100mA (approx) mains transformer from an old phone charger. I'll do up a version with the 1j29b as audio P.A. as the 1j18b is only suitable for about 8mW. The 1j29b should do 100mW @ 45V. But the advantage is that the whole circuit only needs 2 x PP3 and 3 x AA cells.

Note that 4 x AA cells is too much voltage.

Works well at 6 x PP3 (main difference is added audio amp level).

At higher supply voltages the "regenerative" adjustment is very sharp due to much higher gain. So it's actually easiest to tune the radio at 2 x PP3 (18V) HT supply. I think using a 1j29b for "decent" speaker drive needs 40V to 70V HT (45V), in which case a resistor + capacitor to reduce the supply volts on the RF stage to about 20V would be a good idea.
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Old 29th Jul 2011, 9:57 pm   #110
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Default Re: Russian Military Subminature "pencil" valves

Base/box/panel and frame/loop aerial taking shape for a one valve regen radio:
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Old 30th Jul 2011, 9:06 pm   #111
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Default Re: Russian Military Subminature "pencil" valves

I'll blog about the construction of the radio here. http://www.techtir.ie/blogs/watty/miniature_valves_3

Next on this thread I'll compare Triode, Tetrode and Pentode modes of the 1j24b, 1j37b, 1j29b and 1p24b.

I'll look in detail how to use the 1j24b or 1j37b instead of the DK96 as frequency changer/Osc (mixer osc).

I have a simple SE Class speaker amp using 1j29b. Next is to test the Class AB PP version

Then 8W to 12W AF and RF amps with the 1p24b.

BTW
The glass on the 1j24b low power Pentode is about 0.78mm thick! I'd imagine the glass is thicker on the 1p24b-r which is ribbed!
What thickness is EF86 or DF96 glass?
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Old 30th Jul 2011, 9:36 pm   #112
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Default Re: Russian Military Subminature "pencil" valves

How's about using one of your sub mins as an IF amp/Q multiplier in your designs.

Cheers
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Old 30th Jul 2011, 9:45 pm   #113
neon indicator
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Default Re: Russian Military Subminature "pencil" valves

I'll be doing a complete SSB/FM/AM/CW receive and transmit Superhet covering 137kHz to 108MHz in 11 +1 bands.

Stay tuned

(see https://www.vintage-radio.net/forum/...ad.php?t=71394 for some thoughts on it)
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Old 4th Aug 2011, 10:04 am   #114
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Default Re: Russian Military Subminature "pencil" valves

Added page with construction pictures too big for here :
http://www.techtir.ie/construction/herge-radio-base

Working with no external aerial/earth, but quite faint.
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Old 7th Oct 2011, 11:41 am   #115
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Default Re: Russian Military Subminature "pencil" valves

Quote:
Originally Posted by neon indicator View Post
The filament volts are only critical for long life. Also at higher powers there is more filament current from "cathode" current, rather than LT supply. The valves designed for NiCd batteries hence the 0.9V to 1.4V spec sheets. NiMH are bit more than NiCd on average and Alkaline a good bit more, hence the recommendation of series filament resistor. Also has the advantage of bias -0.25V to -0.5V more negative with grid if which desired can be an advantage........

........It's only at very low supply volts with lower loads that there is any advantage to non-Pentode operation. Above 24V HT, Normal Pentode connection is best.

What kind of transformer were you using here?
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Old 14th Oct 2011, 1:26 pm   #116
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Default Re: Russian Military Subminature "pencil" valves

I'm not any longer posting here Piter. Apart from this post obviously.
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