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Old 14th Apr 2013, 7:36 pm   #1
Valve-Man
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Post Valve identifcation - battery powered TRF circa 1930's

Greetings.....

I'm trying to identify a first-stage(?) five pin valve in a two valve (the second valve is an Osram LP2) home-brew TRF receiver using plug-in SW coils. I have no circuit diagram and know nothing of the radio's history - but am guessing that while the components appear 1930's vintage, the wiring looks "as new" and that it may be a fairly recent home-brew project based on a 1930's-era circuit.

(However, my efforts to find a similar circuit on the internet have drawn a blank. The best bet for identifying the mystery valve might be to track down a two-valve battery TRF circuit using a 4 pin LP2)

The mystery valve is four and a half inches long from top to the end of its five pins including a centre Cathode and is of the clear-glass balloon type with polished black bakelite base. There is no trace of any markings re type or anything else.

Given the wiring link between the heaters of the mystery and LP2 valve, both will require two volts for the filaments and are probably of the same era.

Unfortunately, I have no idea how to transfer an image of the mystery valve or a sketch of the TRF circuit onto this message. But if any Forum member PM's me with a personal e-mail address, I could attempt to send them an image of at least the valve. (I'd be happy for it to appear on the Forum).

Any advice would be much appreciated - I've never encountered battery-powered valves of this vintage.

Thank you and best wishes.

David (Valve-Man)
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Old 14th Apr 2013, 8:40 pm   #2
Station X
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Default Re: Valve identifcation - battery powered TRF circa 1930's

Hello and welcome to the forums. You'll find details of how to post pictures here:-

https://www.vintage-radio.net/forum/...ad.php?t=77650
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Old 14th Apr 2013, 9:45 pm   #3
Ed_Dinning
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Default Re: Valve identifcation - battery powered TRF circa 1930's

Hi David, you say it is a 5 pin valve, does it also have a top cap? If so it will be a screen grid (tetrode ) type. The earlier types fitted normally only had 4 pins and no top cap and were triodes.
Either way there are many different types available that will work reasonably well in a set like this.

Ed
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Old 14th Apr 2013, 10:10 pm   #4
Valve-Man
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Default Re: Valve identifcation - battery powered TRF circa 1930's

Thanks for the welcome, Graham, and for the details of how to post pics.... I really must move into the present century re digital technology...

And thanks also for your reply, Ed. The mystery valve has no top cap - just five pins on the base.

What type of valve does this suggest? My first thought was say a 2D2 (double diode) - but pics I have seen appear to be smaller and with the glass-balloon part coated.

Another question: is there are commercially produced battery-eliminator available for valves with a 2v LT and 150v (max) HT requirements? The only one I've seen advertised supplies 1.4v and 90v.

David
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Old 14th Apr 2013, 10:22 pm   #5
Mr Moose
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Default Re: Valve identifcation - battery powered TRF circa 1930's

Hello,

A five pin valve with a centre cathode is sounds like a mains valve, probably with a four volt (or higher voltage) heater.

Most battery valves have inverted V or W shaped wire cathodes and except for output pentodes (or beam tetrodes), have four pin rather than five pin bases.

We really need to se a picture of the valve to be sure what it might be.

Does the valveholder have all five pins connected?

Yours, Richard
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Old 14th Apr 2013, 10:46 pm   #6
Valve-Man
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Default Re: Valve identifcation - battery powered TRF circa 1930's

Hello Richard,

All five pins are connected and are on the base of the valve. Assuming it's a British base, I assume the centre pin (cathode) is 5, with the others on the outside edge of the base (1,2,3,4) numbered clockwise when 1 is directly below 5.

As mentioned, the heaters of both valves (mystery and LP2) are wired together, so I assume both take 2v and are battery-powered. (There's also no mains t/f on the chassis).

I probably should be looking for a battery valve with five base pins of 1930-era. Does anything fit the bill for a two valve TRF circuit?

D
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Old 15th Apr 2013, 12:50 am   #7
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Default Re: Valve identifcation - battery powered TRF circa 1930's

There are a few B5 based tetrodes/pentodes with 2V filaments, but they all seem to be output valves of one sort or another like KT2 or 220OT. One of these might well work as a detector or RF amplifier, but it wouldn't exactly be ideal for the job.
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Old 15th Apr 2013, 8:06 pm   #8
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Default Re: Valve identifcation - battery powered TRF circa 1930's

Here's a pic of the mystery valve.... apologies for quality: it's my first attempt to "up-load" a pic.

D
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Last edited by Station X; 16th Apr 2013 at 7:24 pm. Reason: Pictures added.
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Old 16th Apr 2013, 8:17 pm   #9
PJL
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Default Re: Valve identifcation - battery powered TRF circa 1930's

A not too old homebrew I think. The pic is not good but I would guess that is an output valve, possibly Mullard PM22A. However, its not uncommon to find wrong valve types in old equipment.
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Old 16th Apr 2013, 8:56 pm   #10
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Default Re: Valve identifcation - battery powered TRF circa 1930's

Hi David, yes possibly a home built set but it looks like an HAC (heard all continents) kit set of the late 40's and 50's. These could be supplied with different coils for different ranges. Later models used miniature battery valves from the DK9* range .
Is the centre pin on the valve base connected?

A check of valve data for 2v valves reveals there is an H2D triode with an internal diode connected to the centre pin. The HD 22, 23,24 are similar devices and are later (40's ) valves.
I would normally have expected something like an HL2, L21, PM2HL on a 4 pin base to be fitted here.

Ed
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Old 17th Apr 2013, 9:50 pm   #11
Valve-Man
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Default Re: Valve identifcation - battery powered TRF circa 1930's

Thanks PJL and Ed for your helpful replies - and thanks also to Station x (Graham) for posting the pics ..... something that proved beyond me.

Having taken a closer look at the circuit, I now think it may be a regen rather than TRF. (You can see a choke in the under-chassis pic connected to what looks to be the anode (Pin 1) of the LP2 via a pin on the plug-in coil holder at one end - with its other end going to the "IP" tag on the t/f that can be seen in the top-side chassis pic.

(Is the T/f (with tags marked "IP and OP on one side and OS and IS on the other for audio? And what do the markings "IS" and OS" stand for?

Also, can anyone identify the large square component with fixed vanes (they don't open as with a varialble tuning cap) to the right of the LP2 valve holder (white coloured, top left)? It's connected to a large knob on the front panel of the chassis via a spindle extension.

The knob has a short 'travel' and doesn't move the fixed vanes in the body of the component. One of its connecting tags goes to chassis earth and one pin of the coil-holder; the other goes via a small trimmer-cap to the same pin and to a second one on the coil-holder. Is it a reaction control?

I'll try to draw the circuit - and perhaps (with Graham's help) even post it ..... but only when I can find the several hours this will take.

Thanks again to all who've contributed to this thread - it's a real education for me.

D
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Old 18th Apr 2013, 9:17 am   #12
Ed_Dinning
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Default Re: Valve identifcation - battery powered TRF circa 1930's

Hi David, Yes it is a TRF, but with reaction (or regeneration if you prefer) as a means of increasing sensitivity. The square cap is a solid dielectric type, for reaction control, typically about 300pF. This is normally connected from the anode through a winding on the coil to vary the feedback.
Transformer is coupling between first and second stages, typically 3 to 1 ratio. (In Pri, Out Pri, In sec, Out sec) Often has o/c windings due to fine wire used but can be re-wound.
If you can find some books on radio (Practical Wireless circuits ~ FJ Camm or similar) you will find your typical circuit. It may have slightly different arrangement of component but will be basically the same.

Ed
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