Hi.
I am looking for a speaker transformer for my "Wilco" portable radio.
To save questions, its a 4 valve battery unit using a 3W4, 1AS5, 1U6 and a 1AM4.
The radio itself is about 7X5X2 inches (about the size of the average 1950's "transistor" portablle, and uses a 67.5Volt and a 1.5Volt battery.

I do have the original transformer but one of the primary windings is broken (and it's the one on the inside of the winding)

I'm currently listening to Raiders v Parramatta on a 1949 vintage AWA personal portable!

As I recall, the speaker transformer in those 50's Japanese pre-transistor radios is quite small.

What size would fit? I have some small transformers approx 40 x 30 x 25 mm that would do the job.

I think the specifications electrically are the same as 3v4, i.e. 10k.
So there should be heaps of wrecked battery sets that used 3v4's.
Physical size might be a problem .
JJ

Thanks guys for the quick response.

I guess these little sets are quite common? I cant find any reference to them on the web. I suppose they had various "brand" names.
Foruitously, there is a well-preserved circuit diagram in the back of the radio.

Anyway, the transformer measures 20X25X30mm with the mounting holes being 35mm between centres.
Knowing 10K is the ideal value, I can have another look around.

Oh, and I hope that Ian's radio is still intact afte the footie result!

Thanks again.
Jeff

Any chance you could scan and post that circuit diagram? I'm not familiar with either that radio or any of the valves in it. The schematic will allow me to fill those knowledge gaps.

I'd heard of (and seen) the usual output valves 3S4 and 3V4. Know nothing of 3W4.

Hi Robbbert,

According to this: http://www.radiomuseum.org/tubes/tube_3w4.html, a 3S4 is similar. The valve fitted to the radio has 3S4SF in brackets under the 3W4.

I will have a go scanning the circuit diagram tomorrow.

Jeff

Wilco Transistor Circuit Diagram

Hi Jeff

Jane will drop in one of those transformers when she's picking up the TV for me on the 10th. You might be able to fit it by removing the outer metal strap. If not, at least you can get the radio running.

I will have a go scanning the circuit diagram tomorrow.

Thanks

Circuit uploaded to Post 6.

Thanks.

The circuit shows 1R5, 1T4, 1U5, 3S4 rather than the ones in your first post.

Your radio has the later low-filament-current valves. They are drop-in equivalents to the ones on the circuit

Thanks Ian.

I didn't verify the valves against the circuit diagram. For the above, I just pulled each valve and noted the type.

Ages ago I temporarily swapped in another output transformer. The radio worked ok.

Jeff

Did some online checking and updated my valve compatibility book.

1AS5 = 1U5
3W4 = 3S4
1AM4 = 1T4
1U6 = 1L6, not the same as 1R5, however the connections are similar enough that it might work by accident - or whoever put the new valves in changed the connections to suit.

Have a look at the brand on the valves.

If they are "TEN" branded (or another Japanese brand - Toshiba?) they'd be originals.

The low filament current series were the last hurrah of battery valves, an attempt to counter the looming threat of transistors. With only a single D cell for the A battery they would have more than doubled the battery life, so they were probably a running upgrade in production.

Like the 12v-only space charge grid valves used in late 50's, early 60's car radios, they were an interesting technology that delayed the inevitable by a year or so.

Would the transformer I mentioned earlier fit in the available space?

BTW my AWA is still intact! It even has all the original AWA black moulded paper caps still in it. The 3S4 grid coupler is slightly leaky but the back-bias compensates for it. Means the battery consumption is up a little but the existing set of 216's and D cells has been in the radio for 3 years now.

If anyone needs them, I have a spare NOS speaker and output transformer for this radio. Both are common victims of battery leak corrosion due to the proximity of the 2 D cells. Oh, and a spare radio in brown bakelite, working but in not-so-original condition with cracks and chips and chassis rebuilt after extensive corrosion. This one had had a hard life!

Thanks for the info, Ian.

I will check the valves tomorrow.

Re the transformer, probably not. There IS a fair amount of room for a bigger tx, but we'll see. It depends on how I make an A battery.

There was a hint of a link on here a while ago, for a rewinder. Anyone maybe email me the link?
Anyone used his services? Approximate cost?

Thanks,
jeff