1949 Sobell 439 Sobellette AC/DC mains 4 valve MW/LW midget radio

[howard]

Hello again,

Sobellettes are odd looking little sets and I'm undecided if I like the design or not. The Sobellette has a 'toaster' style case and was released in 1949, a year before the KB FB10 toaster model and came in a plain brown bakelite cabinet or painted beige, cream, light green or metallic green. I guess they were nicknamed toaster radios as they do look like toasters, and now that this one is working I've discovered that they get very hot too ! The painted examples that I've seen have usually been a bit chipped but that doesn't put collectors off as they sell well and sometimes for high prices. The Sobelette is an unusual (cheap) superhet design with a pentode leaky grid detector and no IF amplifier stage. Lack of gain with this configuration was improved by reaction feedback from the detector anode to a tertiary winding on the first (and only) IFT. Its has no AGC and the volume is controlled by varying the screen grid volts on the mixer. It has 4 valves, a loktal 14S7 and 3 octals, 12J7GT, 35L6GT and 35Z4GT (rectifier).

This set came from another collector for restoration and arrived complete but not working. Its green painted case is somewhat worn and inside above its warped hardboard bottom cover its entirely original chassis was rather dusty and rusty. It still had its complete throw out aerial in good condition, and its original mains lead in not so good condition. There was no way that I was going to power up this set up until several of its wax and electrolytic capacitors had been replaced and its valves checked /replaced, its 14S7 was white inside, the top connector on its 12J7GT had corroded and come off, and the glass envelopes on the other two were loose on their bases. Service data for the Sobellette is available here, I used Trader sheet 939 ....

http://www.service-data.com/section.php/7486/1

All the dust and muck was brushed off its chassis which was then cleaned with white spirit. All its wax and tubular capacitors were replaced, one or two of which were wrapped in cotton tape. There was a split in one end of its 32uF+32uF smoothing capacitor with white deposit around it so that was temporarily replaced with a couple of 32uF 450v axials. All resistors were checked and three were found to be way out of spec so they were replaced. I ordered four valves from Mike Lewis and a NOS 14S7 and good used examples of the other three arrived. The valve bases were cleaned with Servisol 10 and the valves fitted and then the waveband switch and volume potentiometer cleaned with Servisol 10. The set was then powered up and the amp was working but there was no signal. All the coils were checked for connectivity/resistance and despite many of their tags being wobbly and loose they were all intact. I wasn't sure about the state of its IF transformer though as the braided cable out of the top of its can was coming away so I took the set over to Ron Bryan to take a look at it.

Ron's signal tracer produced a tone when applied to the detector anode, but nothing when applied to the mixer anode. The IF was also found to be unstable when the screened cable connecting the IFT to the detector grid (top cap) was handled, so the IF transformer was taken off the chassis, its can removed, and inside it was discovered that the black ground wire was broken at the braid end, a winding was found to be open circuit and another winding had two out of three strands of the litz wire broken causing a much higher resistance than stated in the Trader sheet. The ground wire was soldered back in place and all broken windings were repaired by tinning the wire strands and resoldering. The IF transformer was replaced, the set powered up but still no signal. It was then discovered that the local oscillator was not running on either band. The 350pF mica MW padder capacitor was then found to have dropped to less than 10pF so as a temporary measure a mica capacitor of similar value was fitted and the set at last started to work.

I obtained from Mike Lewis a selection of used mica capacitors, and a NOS 32uF+32uF smoothing capacitor which was fitted. The loudspeaker cone was coming away from the frame around the edge so that was stuck back using Evo-stik glue. The original worn mains lead was replaced with 2 metres of modern but authentic looking 2 core braided cable and the set was then taken back to Ron for the 350pF mica capacitor to be replaced and for realignment.

The MW padder capacitor was replaced with 300pF and 50pF mica capacitors connected in parallel. IF alignment done as per Trader sheet including adjustment of reaction capacitor C23. RF alignment was then attempted but abandonned after the trimmer caps on the variable capacitor were both found to be broken. I advertised on the forum for a pair of trimmers for the tuning capacitor and Alan aka phasedout responded and sent me a spare tuning capacitor. On arrival it was taken around to Ron, its trimmers removed and then soldered on to the Sobellette tuning capacitor, a perfect fit. RF realignment was then completed and it peaked up very well.

No restoration was done to the case as its owner preferred it left in its original condition. I did however flatten its bottom cover by steaming it, and also reinstated the print on its dial which had worn away, using black Tamiya acrylic paint.

This little set works well and with its throw out aerial fully extended it manages to pick up most stations on MW and LW, it even manages to pick up RTE on LW which is good going. The dial lamp lights up correctly too as its Brimistor still works despite it being rather corroded. For a little valve radio with its 5 inch Elac loudspeaker it sounds OK too. My thanks to Ron for his help getting this radio working well again.and to Alan for providing the bits for the tuning capacitor.

Howard

[Lloyd 1985]

Hi
nice work! sounds like this set was a bit of a challenge
I personally love these sets, I don't have one, but its on my list of sets to get my hands on! need to make more room before I buy any more radio's though.

regards,
Lloyd.

[AlanBeckett]

Howard,
A splendid restoration, although I have to say that beauty is in the eye of the beholder
Alan

[howard]

Originally Posted by Lloyd 1985

Hi ........ sounds like this set was a bit of a challenge .......Lloyd.

Its chassis arrived in a rusty state which having seen a few pics of these is not that unusual, and before I started in earnest I checked that its dropper was OK and that there was continuity through its more fragile looking coils. It needed a lot doing to it but the total cost of parts came to only £27.50.

Originally Posted by AlanBeckett

Howard ...........I have to say that beauty is in the eye of the beholder
Alan

It certainly is an unusual looking set .........

Howard

[Steve_P]

4 valves faulty in one set! That's rare...

Interesting sets as you say, because of the cabinet design. You either like it or you don't...

Cheers,

Steve P.

[Neil Purling]

Is that strange green tone the result of under-exposed photography or flourescent lighting? The subtle green of the KB 'Toaster' seems nicer.
As you were doing the job for a client, then you have to respect their wishes.
Because it is a paint coating the temptation to re-spray the case or whip the paint off and polish the natural Bakelite would be strong.
I favour a Wedgewood Blue Jasper shade myself, but that's my own taste & opinion.

I was tempted by one of these briefly. Then I remembered that I had a kit radio with the same circuit. It suffered badly 2nd harmonic with images . My BBC local on 202 metres re-appeared at 404. Does this radio have a trimmer to pre-set the sensitivity?
Get it too high and it would howl on a strong signal.
Were these radios marketed as 'second sets'?

[Sideband]

Originally Posted by howard

Sobellettes are odd looking little sets

They're revolting.....! Well beauty is in the eyes of the beholder so fair enough to anyone who likes these. To me they look more like a room heater (probably not far off) and that horrid green looks like it's been painted with left-over paint from the bedroom and the owner was wondering how to use up the last of the paint in the tin!! I'm sure they would look better in the normal bakelite brown.

Well done for fixing it anyway. The only thing interesting to me about these is the rather odd circuit which, as you say, dispenses with the IF amp. Actually I thought this set used a regenerative I.F stage rather than a regenerative detector. Probably getting it confused with another. From that point-of-view, I would enjoy getting one working. I wouldn't go out of my way to find one of these but if one came along, I'd restore it and probably keep it.


SB

[ronbryan]

SB

The regeneration is at IF, but it is taken from the anode of the leaky grid detector and is fed back to the IFT tertiary winding via trimmer cap C23. The detector anode load is split presumably to isolate the reaction feedback from the detected audio and to allow a shunt capacitor to remove the unwanted IF before passing it to the o/p valve.

Ron

[Sideband]

Ah that makes sense. I seem to remember that the I.F amp is used in a somewhat unconventional way when used in P.U mode? The I.F amp acts as a triode af amp to give more gain to the P.U?


SB

[howard]

Originally Posted by Neil Purling

Is that strange green tone the result of under-exposed photography or flourescent lighting?

The pic was taken outside on a dull day and my camera insisted on setting off the flash. That is the correct colour.

Originally Posted by Sideband

They're revolting.....I'm sure they would look better in the normal bakelite brown.......... SB

Perhaps we should have a poll on who likes the Sobellette design and who doesn't

They definitely look nicer in the standard plain bakelite finish if a little austere, and as this one has no chips or cracks it would look better if its paint was stripped off with Nitromors and the case polished, it would only take a couple of hours work. I suspect that most of the unmarked painted ones have been resprayed.

Howard

[IJK2008]

Howard

I stripped a cream one with worn and scraped paint. The bakelite came up nicely and I personally really like the design.

As usual you've done a fine job.

Ian

[Sideband]

Maybe if someone has a plain bakelite one that has been polished, they could post a picture here and then we can compare.



SB

[IJK2008]

SB - will do but it will have to be tomorrow.

Ian

[geofy]

Another good restoration on what at first looks a near impossible task. I quite like the styling of these, though it could get confusing at breakfast time!

The chassis could have the rust neutralised with a rust removing gel, it would take a little time to do but stop the rust getting worse, this is one place where WD40 is useful in coating the metal areas after any treatment. I use it on speaker frames as well.

[phasedout]

Hi Howard, i think the Sobellette, set looks great as it is, its origional, some re-vamp cabinets, some dont, depends on the state of the cabinet etc, i am glad to see you have it working, after all your hard work great effort, you were welcome to the bits...kind regards...Alan.

[IJK2008]

Here's my 'plain bakelite' version to compare with the coloured finish.

Ian

[Sideband]

I think it looks marginally better



SB

[minor8hp]

Just bought one (in dirty speckled green). The jury is out on this one ...Stylish art deco or naff?

[Peter.N.]

My father bought one of these Sobells in about 1949 and I still have it and it works! It replaced the Lotus AC2 which he gave to me and I pulled it apart! Mind you it was only about 25 years old then.

Peter

[mark pirate]

I personally like the look of these sets, if i get a scruffy painted example, i will strip it & polish it's natural bakelite.

Mark