At last; mystery 30's Python console.

[Tim]

Back by popular demand(hopefully!) another of my success stories. This one concerns a "mystery" 30's console set brought to me about two years ago, but I have only just got round to finishing the report! There have been a couple of threads about it, including pictures.

https://www.vintage-radio.net/forum/...ghlight=Python

With befores and afters.


Since then a couple of sets of similar age and internal construction reminiscent have appeared on the forum, so hopefully this write up will be of use to someone.

“PYTHON” CONSOLE SET
Valves FC4, VP4, 2D4,KT41 Rectifier VU39 (UU5)
AC mains powered. MW/LW short superhet?
Circa 1937

When this one was dropped off, SWMBO really didn’t approve. You see she was glad to see the back of a massive guitar amp that had just been collected, having been repaired the week before, and didn’t relish this”hideous monstrosity” (her words not mine-I think it’s quite attractive) taking it’s place.

The only clue to the origins of this set was a small plate bearing the name “Python Radio”-but no one seemed to have heard of them so that didn’t help much. After a quick look at the valve line-up, I reckoned it to be a basic (or short) superhet (that is, there is no small signal audio valve), from the mid to late 30’s.
These work well in areas of good signal, but need a decent aerial.
I also noticed the mains cable was crumbling fabric covered VIR so would have to be changed before testing. The set was also equipped with a connection for a mains aerial, maybe acceptable when built but I don’t really approve of them these days. The audio transformer and what looked like a mains energised speaker was connected to the main chassis by five separate wires(all yellow………..) so since I have no service information those will have to be labelled before they break off.
The top cap of the VP4 was found broken off, it’s bakelite fitting still attached to the set wiring, but the valve envelope seemed intact.
The set had all its knobs and back, so the first thing to do was remove the chassis and investigate!! Actually the VERY first thing was to remove the knobs. I couldn’t loosen any of the grub screws, so the screw holes were filled with fine oil and left for a week or so.
The knobs were then able to be removed, and turned out to be the only thing holding the chassis into the cabinet, all mounting screws were missing.
Once removed from the cabinet, the chassis passed all the usual mains tests. A generous length of 3 core mains cable was fitted but since there was no convenient method of cord grip a knot was tied as a temporary measure until something better could be devised.
The original HT smoothers are contained in a wax paper block, but presumably these went open circuit long ago, as replacement grey Radiospares types have been fitted sometime in the past. Curiously the original HT capacitors are still connected, as is a 25uF cathode by-pass inside the same box. I shall probably fit the replacements inside the box.

Mains checks were all OK, as was the output transformer(phew) and an earth terminal was provided under a nearby screw and nut. The rectifier valve was removed, the HT bench PSU connected to the socket’s cathode pin via a 47k resistor(and –ve to chassis of course) and the HT caps left to (hopefully) re-form. The current drawn by the set was a few tens of milliamps but not excessive, but hadn’t significantly reduced after about 45 minutes though so replacements for the replacements would have to be found. A value of 6uF was read off the capacitor box, a value not commonly found these days. I would probably use a 4.7uF/450 volt here, as it’s very nearly 5uF anyway, and electrolytic capacitors are very often of slightly greater value than the markings. The second capacitor could be a slightly higher value since it is separated from the first by the speaker energising/ht smoothing coil. I think I used a 22uF/450volt here.
All the HT caps in the set were disconnected (but only at one end, so I would remember where to re connect them!),and the HT PSU connected directly to the set. Next the output valve grid coupling capacitor was identified, checked (ooh look it’s leaky…………) and replaced with a modern 400 volt polyester type.
Before testing the VP4 was subbed with an AC/VP1 (also 7 pin), the original Mullard valve put aside safely in a small cardboard box for further work on the top cap. The original valve must have been an early one as it still had a screw cap arrangement. The AC/VP1 had a large size pip, so a croc clip was implemented as a temporary adaptor!
With all valves except the rectifier aboard mains was applied again, and HT switched on. At 200 volts a hiss was heard from the speaker, and an audible buzz could be produced by the screwdriver test at the volume control wiper. No stations on radio though, even with a decent aerial. The static seemed quieter than usual.
Out came the multimeter again, and a few measurements at valve pins confirmed a lack of screen volts on the FC4 and VP4. This was traced to an open circuit 50k resistor, which was temporarily replaced by a 47K 1 watt.
Now we had stations on both bands, (but not very loudly)all over the LW band but only below 300m on the MW band. I have had these symptoms before in a Marconiphone 264, which turned out to be a faulty-low emission-MX40(FC4) frequency changer.
I am embarrassed in respect of an FC4(I don’t have one!-except the old MX40 as an emergency, emergency replacement) but did happen to have a set “in” with a decent one in, so at least I could prove my theory before ordering a scarce and expensive replacement. Temporary substitution proved my theory and a new FC4 was duly ordered.
With a new FC4 the set worked well, bringing in stations all across both bands, but was still rather quiet. I replaced the remaining waxies at this juncture, but although performance improved, volume didn’t
Finally the “quiet” fault was traced to an intermittent (but later went o/c-that’s how I found it!) speaker field/HT smoothing coil. A stout 2K2 resistor was tacked across the connections to the duff coil and a permanent magnet speaker connected to the speaker connections of the original output transformer.
On subsequent test, I forgot the volume was nearly at maximum and the family got a blast of KT41 in full stride!
The rest of the tests on the set were carried out with this temporary arrangement in place, until I could get the speaker/field coil sorted out.
Performance was much improved with all the waxies replaced.
The original VP4 tested OK so a small part of the glass around the broken off top pip wire was carefully filed away, and a short piece of wire thin wire soldered on. This was in turn connected to the bakelite top connection which was epoxy-ed to the valve envelope. The valve proved fine in the set.
The output transformer is mounted on the speaker in this set, so we needed at least five wires to connect it to the gubbins of the set. As received these were a messy nest of yellow wires, which were quickly traced and labelled at each end before any snapped off and created a need for some detective work to discover where they used to be connected.
As part of the restoration of the set, this mess was replaced with some trailer cable, allowing the 5 cores to be run neatly in the cabinet.
The old wax paper box capacitor was opened, old caps removed out and replacement modern capacitors fitted inside, and the under chassis wiring generally neatened up.


CABINET
.The customer wanted “the full Monty” on this one, and although I am willing to tackle the electronics part of restoration (and even win sometimes!), restoring wooden cabinets fills me with dread! Fortunately this one was really a simple box with no funny shapes or curves, and was actually in quite good condition so was good for a beginner like me!
All the fittings were stripped from the cabinet, and an electric sander used to remove traces of the original finish. Once a couple of coats of white spirit were allowed to dry several coats of quality wax furniture polish applied. The whole cabinet was then buffed to a reasonable shine. OK probably not a good as the original French polish(dread? French polishing is the stuff of nightmares to me!) but certainly better than when it arrived.

The cabinet fittings were re installed, speaker cloth and dial glass cleaned, and the replacement speaker/transformer/energising coil re-fitted.
The back was in sufficiently good order not to require any attention other than the cloth re-gluing.
The knobs were cleaned and the indented writing filled up with silver wax crayon (try your local art shop or brass rubbing society!)
The set was checked and then run for some 8 to 10 hours, with no problems before being handed back to a delighted owner. Performance was actually not bad for a short superhet, with good volume on lots of stations and pleasingly low levels of hum.
Incidentally the choc block seen in the picture was to join the extension speaker wires back from the speaker mounted transformer to the ext sockets on the back of the set, so no mains is involved.

[Tim]

STOP PRESS!! Mystery solved.

Mike Barker confirmed this one only TODAY as definately a Defiant from 1934. His comments can be found at the link at the top of my post.

The top link is via the search thingy. Just in case it stops working or any other problems.


https://www.vintage-radio.net/forum/...ad.php?t=36406