Tale of a Shaftesbury miniature 5 valver

[Top Cap]

I miss my long departed friend George, who ran the village Radio & TV shop, but one radio in particular always revives some memories, so I set my heart in getting one. Not one of your usual British makes but a tiny Japanese valve radio. The story goes that when George first stocked them he seemed delighted in the fact that they were very cheap and he was likely to sell a lot of them and make a handsome profit in return. Some months later when I visited the shop, he had them all stacked up in the workshop, forgotten and forsaken. Why? I asked, “Bloody capacitors – blown the valves” was his reply. The valve heater dropper capacitors had gone short circuit but he refused to let me have the remains, the reason I never ascertained. Anyway, up came a similar radio on an internet auction site and I was soon the proud owner of what was advertised as a non working radio but the valves lit up. Hmm, so it looked likely that the capacitor was ok. These radios are amazing considering there are 5 valves in the small plastic case, this particular one was a Shaftesbury and it had a surprise. Instead of a voltage dropping capacitor it employed an auto transformer for the heaters, but nonetheless, the large plastic headed screws pre-warned me that the chassis could be live. As I removed the rear panel I noticed that someone, with more bravery than I, had installed an earphone socket but this was now disconnected, along with the speaker wiring. When the chassis had been removed, a good visual inspection showed that the main 40+40 smoothing blocks looked kind of weepy so on went the Multimeter to monitor HT levels as I wound up the Variac controlled isolated mains supply. As the 35W4 rectifier began to warm so up came the HT, slowly increasing the supply bit by bit, spurred on by the lack of smoke. But HT seemed a little low at 85V when a 220V input was applied. There was no sound at all, not even a faint hum and the Multimeter showed HT on only one side of the output transformer.This is an incredibly small transformer for a 50C5 output valve and surely a replacement would be impossible to find. See attached photo.

In the junk box I found a RS miniature output transformer and though it was for a 3 Ohm speaker I decided to try it. The results were a bit puzzling as now I was getting hum and faint audio but not exactly any volume to fill the smallest of bedrooms.
A buzz check on the volume control proved fruitless and all hopes of a simple 'Not working due to disconnected speaker' fault, slowly vaporised. Vaporised?

The HT on the 12AV6 audio amp was only at 8V and whilst I was measuring this I noticed steam beginning to escape from the main smoothers, wow they were running really hot! . I decided I would have to do something about these before anything else so out came the block and new capacitors were fitted below chassis.
This gave me more space on the chassis top to fit the new output transformer should this finally prove to be usable. With new smoothers in, the HT was a lot healthier but I still had only a few volts on the anode of the 12AV6. A 200pF ceramic capacitor had decided to become a 2k resistor so this was removed and replaced whereupon the radio burst into life and sounded quite good. The current through the replacement 30mA output transformer was a little high at 46mA so I increased the 50C5 cathode resistor without any loss of sound quality.
You can see the replacement transformer in the attached photo, sitting behind the 12AV6 and the 50C5.After a bit of cabinet polishing, the radio came to look quite good and my under chassis wiring has made the radio far neater than when it was first made!
Not quite the same make and model I was looking for but nice to have and another bit of valve history rescued from landfill. I never thought I would ever find a use for that transformer; it had been in my junk box for over 25 years!

[Tim]

Nice job.
See, NEVER, NEVER throw anything away!

[Steve_P]

That's incredibly small for a valve set isn't it. The Japanese were (and are) excellent copiers - this is the sort of thing they had in the USA and chances are one got into Japanese hands. The name Shaftesbury is because this was intended for the British Market.

There can't be many of these around - a rarity as well as a quirky item.

Bet you can't get a circuit for it!

Cheers,

Steve P.

[Tazman1966]

A facinating story TC! Thanks for sharing it with us. Does the set run really hot?

[newlite4]

Yes, these are fascinating little sets, they were made in Japan up until the mid 1960s, and were based upon the "All American Five" layout. I have this version as well as a similar model that has the dreaded capacitor dropper - when it goes, the result is costly to say the least .
Thankfully, the makers had the presence of mind to paste circuit diagrams on the rear panel in a similar way to those early shirt pocket sets.
The Japanese were in no hurry to abandon valves, instead allowing them to run alongside transistors as technology progressed.
Neil

[Top Cap]

Yes Tas, the radio does get quite warm when run for just a few minutes. The makers have provided some vent holes underneath as well as a metal ventilation grille along the top of the hardboard back. Not the sort of bedroom radio I would trust though if one happened to fall asleep . It will just take its place among the others and have its occasional run. There is a circuit on the back but sadly a bit damaged, I will attach a picture of it for you Steve.
Cheers
Les

[HMV 1120]

I used to live in shaftesbury - home of the Hovis bike add. A set worthy of the name ^^

[Skywave]

Looking at the cct. diag., I find it amazing that a 5-valve superhet can be designed with so few components. A 5-valve TRF would probably have more innards!
Excellent repair / restoration, though.

Al.