ALLSCOTT III 3Valve TRF

[David Simpson]

Folks, does anyone know anything about ALLSCOTT & their TRF's, please ?
A Forum chap had a thread back in 2016 about Scottish wireless makers, and seemingly Allscott were from Perth. Possibly they just provided generic circuit designs from the 1920's. However, the lovely oak (smoker's) cabinet is jolly well made, and the patterned ebonite front panel is a joy to behold.
Sadly, the circuitry & components have been extensively "got-at".

Regards, David

[PJL]

Nice looking set and it looks like many of the parts are original. Do the disconnected small plugin bits on the right have any markings? There is reference on radiomuseum to Radio! Radio! here https://www.radiomuseum.org/r/scott_allscott.html.

[AC/HL]

They look like McMichael clip in mica capacitors

[David Simpson]

Thanks, PJL, for the Radiomuseum link. As Bill says - mica capacitors, .01uF
One of the two filament pots has completely lost its resistive winding. Aerial coupling coils & mountings are non-existent. Much of the interconnecting wiring has been clipped away. But all is not lost, as I've a decent box of TRF spares & copies of several 3 valve TRF circuit diagrams. Although I would like to get hold of the correct one.

Regards, David

[Ed_Dinning]

Hi David, I have some resistance wire here id you want to rewind the pot

Ed

[DuncanLeece]

Good evening David,
Lovely set. Here is a wee snap of my five-valve Allscott portable, which I think is pretty original, although like so many of my sets, as you know, I have never had time to delve much into it.
If you think studying the circuit, or looking what parts it uses, would be any help, you are most welcome to borrow it. I must be due you a coffee anyway.
Allscott sets are pretty rare, so you know your duty......you have to get it fettled!!!!
best wishes
Duncan

[David Simpson]

Now Duncan, that is one helluva nice looking set. And, the same lovely patterned ebonite for the panel. Is yours a 3 valver ? This one has a switch for either using 2 or 3 valves. No Grid Bias supply, just LT, and HT, and then - EHT ! All etched into the rear ebonite strip for all the terminals.

Regards, David

[David Simpson]

Folks, I've put out a Wanted post for some hard drawn 26SWG tinned copper wire, tightly sheathed in coloured lacquered cotton. See picture (d). I've managed to salvage a few decent lengths. See picture (h).
I've also had a good detailed shufti at Duncan's Allscott Portable, my - what a lovely set. Far more up-market than my wee TRF. Sadly, his circuitry is totally different than mine, so shall re-build my set as a basic TRF, using a mix of design between Mr S - T & GECoPhone circuitry. As sadly, I've been unable to locate or obtain any Allscott circuit diagrams at all.

Regards, David

[David Simpson]

A post for "Repair Nightmares" thread. Guess I'm DoD, & "Should've gone to Specsavers". Please read 18SWG NOT 26SWG.

Regards, David

[David Simpson]

As I've said in my "Wanted" thread, someone has kindly donated a couple of small hanks of plain DCC tcw. 22SWG instead of 18SWG, but just as stiff.
There was just enough salvageable 18 swg red & black wire to reconnect the LT circuitry to the filament terminals on the valve holders. All tickerty boo with the 3 chosen valves powered up filament wise. There is a bit of old red & some yellow & blue salvaged 18swg, so will see how far that goes with wiring up RF, AF & Grid circuitry, and might only need a small amount of the now off-white 22swg.
Valve line-up chosen is - - PM12A, PM2DX, & an LP2. The original Ferranti AF3 T/F is still ok, but have a spare NOS one, anyway.
If anyone is needing some 22swg DCC tcw, please just ask.

Regards, David

[HamishBoxer]

Looking good.

[Radio Wrangler]

Some seriously good fettling going on there!

David

[Mr 1936]

Hello David

I have an "Allscott" 3 valve receiver in my collection. The front panel is smaller and less elaborate than yours, with just tuning and reaction controls plus a filament switch. It appears identical to figure 239 in "Radio Radio" which dates it at 1928. Yours has the feel of something from 1926 or 1927.

When it gets above freezing point in the shack I will try and dig it out and get more internal details if that would help. I haven't looked inside for quite a while, but don't remember it being "got at" in any way.

[David Simpson]

That's great news Mr 1936. Yes please, I'd appreciate any circuitry details you can provide. At the moment I'm rebuilding it as a basic 3 valve TRF, due to the lack of any evidence of a reactance or diff. condenser & associated circuitry. It didn't even have any aerial or tuning circuit coils, so I'm just fitting a pair of bog standard Lewcos type ones. The rest of the circuitry will be a mix of what is inside my 3 valve GECoPhone, & my ST400, coupling & decoupling-wise. HT1 will be 75V(for the PM12A's screen), and HT2 will be 150V for all the Anodes. There were no GB terminals on the long rear ebonite terminal strip, but evidence of a wee GB battery in the front r/h corner internally.
That big 2Valve/3Valve change-over switch in the top r/h of the front panel seems to be a complicated device for such a basic set. So will just use it as an HT/GB on/off sw. for all three valves. Interestingly, both Filament pots start of their acw to cw traverse on a taper of the resistance wire former, hence act as off - low volts - - max volts. Negating the need for a separate Filament on/off switch. But only the l/h pot was ever used.
Being based in Perth, in the Scottish Highlands, me thinks the Allscott design engineer liked a dram or three. By a quirk of fate, my Fyfe & Simpson ancestors all came from Perthshire(Glendoick & Kincardine on Forth). So this set is special to me.

Regards, David

[David Simpson]

Well, that's the TRF finished circuitry-wise. Just the wooden cabinet to clean up & polish. Ended up using a 220VSG instead of the PM12A. Two Lewcos coupling coils :- a 60X for the Aerial, and a 60 for the Grid tuned circuit. Tuning range is 730KHz to 1700KHz, with 1100KHz mid-range. Just two or three dominant UK stations, and plenty of continental ones. All pretty clear out of my Browns headphones. Of course, adjacent channel reception is an issue. But, quite frankly, this basic Allscott is as good as my more advanced ST400.
The effing DCC wiring is a sod to strip, as the outer cotton likes to fluff out even after careful cutting with a hobbyist's scalpel. Plus my efforts at coloured lacquering were prone to flaking if handled too much.
I'll draw up a half decent coloured circuit diagram & post it with my final report. Hopefully Mr 1936 will recover his Allscott from his shack & get stuck in.

Regards, David

[Mr 1936]

Here are the first batch of photos of my Allscott 3 valve TRF set. I think the use of 3 triodes dates it to about 1927, just before the era of the RF tetrode. The cabinet is made by Habilock and is 13.5 inches wide, 8.5 inches high and 10 inches deep. The front panel is ebonite with an interesting finish, a bit like one of those "engine turned" metal dashboards on a vintage sports car. The components are mostly "breadboard era" types with terminals, and fairly closely but neatly placed. Wiring is by 18 SWG tinned copper wire with a coloured finish, very neatly bent at right angles and using solder tags at the ends. Clearly not a home-constructor job. The only replacement wiring appears to be to the flexible stuff to the three grid bias wander plugs, though the plugs themselves are of an unusual design and probably original.

[Mr 1936]

Here are the second batch of photos of my Allscott. The circuit is an utterly conventional 1-V-2 triode lineup. The aerial connects via an internal Igranic preset variable condenser. The front panel tuning and reaction condensers are both by Polar. A single Colvern tuned circuit (Medium Wave only) feeds a Cossor 210HL with a reaction winding and a reaction condenser of about 150 pF. In its anode circuit is a multi-pile HF choke, plus a Ferranti AF4 transformer feeding a Mullard PM1LF via a rear panel headphone jack which cuts audio to the later stages if a plug is inserted.

The PM1LF has another AF4 in its anode circuit, feeding the grid of the final Cossor 215P. An external speaker is used, via rear panel screw terminals, with a Graham Farish condenser in parallel.

The valveholders are by Lotus for V1 and V2 and by Benzamin (Sprung) for V3. The clip-in grid leak for V1 is 2 megohms and by Graham Farish. On-off control is by a pull swich in the earthy side of the filament circuit. There are two HT rear terminals, one for V1 and another for V2 and V3. Both have a metal clad decoupler.

The 16 1/2 volt grid bias battery sits in two nickel plated brackets which appear original, with three wander plugs - Red for Ground, Blue for V2 grid and Black for V3 grid. Other fixed wiring is Black for Earth, Red for HT +, Yellow for Grid circuits and Blue for Anode circuits.

I haven't yet fired up this set, it appears to be mostly original and well-made but who knows what open-circuit windings I might find - wait and see !

[HamishBoxer]

Great looking set and excellent photos.

[David Simpson]

Great pictures from Mr 1936 (hey - we're forum chums - Bill, John, Peter, ? ). As everything is intact, it bodes well that you'll get it going. Whereas mine had been got-at, with a number of bits missing. No Colvern or any make of coils at all. So I just used some decent Lewcos ones.
Nice to see the same coloured 18swg DCC wiring. And, I guess, that those fantastically etched Ebonite front panels are unique to Allscott.
Is the GB Battery a modern replica ? It looks jolly authentic. As you say, MW only. I've a decent earth matrix under the grass outside, and used my 80m Doublet for the aerial. We need good reception facilities this far north.
So, that's now 3 Allscott receivers in the UK - Duncan Leece's, mine, & yours. Hopefully, this thread will encourage others to check out their shacks/sheds/lofts/etc. & maybe find another one or two.

Regards, David

[Mr 1936]

Glad you like the pictures. Pleased to report that the GB battery is a genuine one (complete with cracked pitch filling !) and may even be as old as the set. The price equates to about £5 in today's money, so just as well the current drain was so low they must have lasted for ages.

I guess Medium Wave only isn't too unsurprising, as Longwave didn't really get going in the UK until Droitwich started in 1934. As an aside, I believe long waves don't propagate too well in Scotland (all that low conductivity granite underfoot).

Regards, John (Mr 1936).