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Unknown early 1930s kit Radio

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Anonymous
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It's got Screen Grid (Tetrode, SG210 or 210SG or similar missing screw cap), Triodes x 2 (2nd is a PM2), and possibly a 4 pin base output Pentode (push on top cap).

Looks like TRF with Reaction (3rd variable capacitor with a smaller knob).

The switch probably is on/off only switching LT. So maybe LW only, or do you think MW? Is the "green" on the coils corrosion or green cotton?

It's almost certainly a kit. Not really a Scott-Taggert, Mullard or Lissen I think, unless there are models I don't know. Though It's got Lissen inter-valve transformers and there is Lissen four valve kit, but it's push pull output.

Why do I say 1930s when it's got 1926 approx style slow motion tuning dials?
Actually, I'd say 1932 /1933 even if the output transformer is original as even up to 1931 kits used either high impedance Reed Speakers or 2K + 2K headphones thus had no output transformer.

The Pentode suggests 1930/1931 at earliest. Could it be a PT2A? I can't find other 2V pentode with 4 pin base and top cap.
Interesting the SG215 / 215G type valve is used by Lissen and the PT2A is in the Lissen Skyscraper 4 Ultra and the Lissen 8044 There are HL2 that look like the two non-top cap valves in the kit. The PM2 isn't that much different.

Or could it have been a 3 valve kit from later 1920s and both the Pentode and Transformer are later additions?
A commercial model with similar 3 valve line up and no 4th (pentode) valve
http://www.radiomuseum.org/r/cossor_emp ... r_234.html

No SG valve for RF, but 3 valves with PM2 as output and similar tuning dial
http://www.radiomuseum.org/r/dibben_cromwell_iii.html

If the Pentode and 3rd audio transformer are a later addition, then it might be a Lissen or Scott-Taggert mid to late 1920s kit?

Seven terminals in addition to Aerial & Earth, so likely 2 x HT, 2 x GB as well as 2V LT.

I'll know more when it arrives inside the next week to two weeks, but I wondered if anyone recognised the design?

 
Posted : 31/08/2013 6:59 pm
EDDINNING
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Hi Michael, that should clean up nicely. It will almost certainly be MW/LW, so look for switches somewhere (top of coils?). If they are variable caps on the top of the coils that is a bit unusual as the cap was an aerial trimmer and normally on the first coil only. Green cotton covered wire is the norm for these.
The biggest problem is likely to be poor joints, especially nut & bolt types. These need a really good clean.
Paper block caps will be leaky, grid leak will have gone high and the intervalve trans may be O/C (or poor screw connections).
These are all easily fixable and you should finish up with a really nice set.

Ed

 
Posted : 31/08/2013 9:21 pm
Cobaltblue
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When I saw this on eBay I was struggling to recognise the coils used as well.

I think the knobs on the top are pull switches for the waveband quite a common trick, they certainly look as if they have more than enough turns for LW

The Wire is green cotton covered. (It might still be rotten inside though)

The design of the tuning capacitors makes me think circa 1930

This is reinforced by the fact that the SG valve isn't mounted through the screen as was the fashion for the first couple of years after its introduction

The coils look very similar to those made by Tunewell.

Very difficult as so many coils looked Similar

It was quite common for these home made sets to use what ever was to hand and the SloMos would have been a big saving. Sometimes sets were rebuilt every few months.

Interesting set and the fact that the output transformer is sat right on the edge makes me think it was a later addition as moving coil speakers became more affordable.

Cheers

Mike T

I don't care if it was a bargain whats it doing on my kitchen table. www.cossor.co.uk

 
Posted : 31/08/2013 9:31 pm
Anonymous
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Sometimes sets were rebuilt every few months.

Sounds like 1995 to 2005 home assembled PCs :)

Yes, I'm leaning to theory it's a 1927/1928 three valve set as the PM2 is often output on 3 valve sets. It would have driven reed horn, reed speaker or Hi-Z headphones (load 2K to 5K so no output transformer). Then the Pentode and large output transformer added in 1932 /1934.

The "buttons" on top of coils might be switches. That will be nice. I never knew that.

I think the Grid Bias battery might have sat where the Pentode and Output transformer is?

A detail from a different set

 
Posted : 01/09/2013 12:28 am
Anonymous
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The knobs on the tops of the coils ARE totally seized wave change switches.

Just brushed and then wiped with damp soapy water

S210 (Tungsram, a bit like SG215), HL210, a wrong valve and PM2 output.
The grey valve with top cap to left near panel is wrong, that's an Osram VS24K, a SG (RF tetrode). It should maybe be an HL210

What I thought was an intervalve transformer is a choke for RF SG valve.

The two large paper capacitors measure bad even on a DMM! The rest must be mica and are OK. The wax bottom and card easily pops off and enough space to snip wires and add a modern part leaving the original in place. Minimum destruction of artefacts :)

I took apart one Slow motion drive, the crumpled white plastic has no markings. Should it have something? The log scale is around the outer edge.

I repaired one Wavechange switch. Easily removed from coil but a pig to free!

 
Posted : 04/09/2013 11:46 pm
Cobaltblue
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Nice Job!

I doubt the markings on the plastic would have completely disappeared!

Most of this sort of tuning scale are just marked 0-100

So it looks as if you were given the opportunity to create your own scale

Cheers

Mike T

I don't care if it was a bargain whats it doing on my kitchen table. www.cossor.co.uk

 
Posted : 05/09/2013 9:00 am
Anonymous
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It does not look so bad now, you will have it working in a day or so.

 
Posted : 05/09/2013 9:31 am
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It's gone on hold now.

Both interstage transformers are open circuit on the primaries.

 
Posted : 05/09/2013 7:59 pm
Anonymous
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I filled one transformer case

It's this transformer (or an identical version)
http://www.radiomuseum.org/r/lissen_lf_transformer.html

Only wax sealing over terminals and card cover, so the unit simply popped out. Iron wires a bit smaller than 1/16th" and long enough to bend over at top and bottom to full height of bobbin/spool.

It is actually 3:1 step up.
The primary is on the inside, hence secondary turns are longer which accounts for winding resistance 4:1 (suggesting both use the same wire size), the Impedance ratio in use is thus 9:1.

A 4:1 turns would be 16:1 impedance already likely too ambitious!

I thought to use a 240V to 12 driving a 240 to 6 in reverse (2:1) to test and later rewind the transformer. Pulling out the iron wire from spool was easy once first few wires out.

I will wind off the secondary and simply wind it all back on when the primary is repaired or rewound.

The back to back sub-miniature UK mains transformers from cheap Chinese transistor sets worked, (240 to 12V, 6 to 240V in reverse to get 2:1) fits in Bakelite transformer case too 😀 The 240:12V one is approx 2800 Ohms mains primary and the other about 2400 Mains Primary.

So now I know as the entire radio is working (as a three tube, I believe the 3rd triode AF preamp and 2nd transformer (also Open Circuit) was added later).

I stripped the panel and board completely and left out the extra triode stage as I am convinced added later, and also I don't have a spare triode nor parts for a 2nd transformer.

I tested initially with a Battery radio transformer and speaker on the phones connection and then with my home made reed cone loudspeaker (3600 Ohms). It works well but the 2nd RF tuning has a couple of spots it shorts as does the Regeneration, which shorts the anode transformer of V2 (HL210) to earth via regeneration tickler coil. I will fix with emery boards.

I replaced the shrunken and bubbled matt plastic on the tuning drives

Repaired the two large paper capacitors and grid leak resistor.

It probably used 75V on SG g2 and 150V HT and maybe some other voltages (90 "B" cells). Using 60 or 72V HT and 120V HT etc from a Winner 120 is fine (80 "B" cells), 48, 69, 72, 108 and 120V.

The PM2 seems to need the full -9V of the Grid Bias pack.

Total consumption with 72V g2 and all other HT at 120V is 9mA
LT is about 480mA (VS24K @180 + HL210 @100 + PM2 @200 mA)

 
Posted : 08/09/2013 1:37 pm
Anonymous
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The "final" circuit

All the HT apart from the V1 VS24K g2 supply are tied together at the minute. I will experiment later.

V1 VS24K Anode supply choke http://www.radiomuseum.org/r/lissen_hf_choke.html
V2 HL210 to V3 PM2 Interstage transformer http://www.radiomuseum.org/r/lissen_lf_transformer.html
V2 grid coupling to 2nd RF coil and capacitor http://www.radiomuseum.org/r/lissen_fix ... _mica.html
The V1 g2 and anode HT supplies decoupling. http://www.radiomuseum.org/r/lissen_man ... nsers.html
One is definitely 2uF, the other 0.1uF to 0.5uF I think, a new 1uF and 0.1uF works in the box (I left the old smaller cap in place.

Original Wiring:

C4 2uF (paper) was on Anode side of L10, HFC. the other end not connected to anything, earthing would kill the signal. The HFC was connected between HT and V1 anode. The ONLY place for a 2uF in such a radio is between an HT and "Earth".
C3 3nF (mica) was connected to connection 1 of 2nd coil (input), but the other end had a short wire that could reach an earth terminal and nowhere else. The only logical place to connect is junction of V1 Anode and HFC L12.

Primary of T1 and T2 are open circuit.
Main LT switch in series with "Earth". But LT - wire connects to Earth/HT- Terminal, the other side of switch goes nowhere.

Flying leads from V3 base filament and T1 secondary presumably for GB supply, no GB wire on secondary of T2.
The PM2 output triode in 4th valve base, but an erroneous SG valve plugged into V3 base (extra AF preamp stage).

The HL210's Grid Leak resistor is intermittent 12M to open circuit. But C5 is in series between VC2 tuning and grid! The coil is (connections 5 to 3) is between HL210 grid and ground anyway, so no grid leak! The resistor is usually wired either on HL210 base or across C5 on these designs. It was wired between V3 filament base and V2 grid base.

So did it ever work? Or did someone mess it up when they added an extra stage, or was it messed up later?

 
Posted : 08/09/2013 2:15 pm
Anonymous
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I have no high impedance phones.
So I used a transformer and moving coil speaker for a demo.

Wired as a three valve (tube) kit Radio. Osram VS24K as RF "SG" Tetrode, HL210 Triode as Regenerative amp and detector, Mullard PM2 Triode as output. VS24K g2 volts is 60, all other HT is 120V. -9V grid Bias. The "Ever Ready Sky Queen" box behind is a spare (no radio or amp in it!) with a 240V to 6V transformer (as an audio transformer) driving a 1950s 4 Ohm moving coil loudspeaker (2n2F snubber/tone correction on primary). There is no amplification in it. It's instead of 4K headphones,

 
Posted : 09/09/2013 11:04 pm
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