Binatone pocket radio

[Jolly 7]

Here is a non-working Binatone Commando pocket radio I bought recently. I've taken it apart in an attempt to repair it. The 9V battery clip had a torn wire, so I replaced it. There is still no sound out of it, just a tiny crackle when I switch it on.
The local oscillator seems to be working ok. Not sure about the audio stages though, will need further testing.
The radio has two IF stages and no audio driver or output transformers.

[Herald1360]

Is the oscillator coil not one of those cans? You need three IF transformers for two conventional IF stages.

How many transistors are there? A transformerless output amp would normally use four.

[Jolly 7]

The radio has five transistors and a diode. There is a round transistor with a black cap which seems to be the oscillator/ mixer and is marked 70. Two of the other transistors are marked F70H301 and F401235. The remaining two transistors have no markings at all and neither has the diode.

[paulsherwin]

What is the speaker impedance? It's not impossible that the output is class A, though that is unusual in radios of that era, even at the bottom end of the market.

I would expect the transistors to be nondescript NPN Si types. You could use 2N3904s/BC548s for the RF/IF stages and 2N2222s/BC338s for the audio. However, there should be one PNP type in there somewhere if the output is transformerless push pull.

[Sideband]

Traditionally the red one should be the oscillator, the yellow 1st IF and the black, last IF. That looks to be an extremely limited circuit since it seems to be lacking a second IF stage and really only a local station receiver. It might even have a reflexed IF stage in an attempt to improve performance.

[paulsherwin]

Yes, it's an extremely cheap'n'cheerful radio to put it politely.

it's an extremely cheap'n'cheerful radio to put it politely.

That is its charm, worth getting going.

[Stylo N M]

Hi, Jolly 7

It's a bit of a long shot, but with the battery connected and the radio switched on, and the volume turned up, tune the radio to a position where you think there should be a strong local signal. Then place the end of your finger over the three legs of each transistor, on the soldered side of the board and press gently, just do one at a time you may hear a signal.

I repaired a transistor radio once like this and it worked for me. It identified a dud transistor in the tuning stage (but it is a long shot)

At least it's nothing lost nothing gained at this stage of the game.

Paul

[crackle]

There may be an electrolytic pulling down the voltage on one or more stages, measure the voltages on the transistors.
Leave the power switched on and it may start to work.
Mike

[Heatercathodeshort]

The coil cores look as if they have been 'twiddled' so may need a tweak up when you get it working. Maybe a broken wire or cracked P/C board.[dropped] Not a lot to go wrong unless someone has connected the mains across the battery terminals. Yes had that quite a few times back in the shop days! John.

[Stylo N M]

I thought that aswell john, that the coil cores looked as if they had been altered, but i didn't like to mension it (also possible wax removal)

Paul

[60 oldjohn]

Originally Posted by crackle

Leave the power switched on and it may start to work.
Mike

Worked for me on a few occasions, but clean any WC switch first. Also heating the oscillator transistor between finger and thumb, I had that transistor to change OC44/45 IIRC.


John.

[paulsherwin]

No switches here, it's a MW only set.

[GeoffK]

This is a similar radio, it works well with surprisingly good audio for its size. It has two 1.5V cells instead of a 9V battery. Five silicon transistors, one silicon diode detector, one IF stage, driver and output transformer with 8 Ohm loudspeaker.

Jolly 7 radio seems very unusual having five transistors but no driver or output transformer. The positive lead appears to be connected to one side of the speaker, this is a bit strange as well.

[Herald1360]

That would work for two possible scenarios- mixer, IF , diode, audio driver, complementary output with capacitor to other side of speaker or else mixer, IF, diode, preamp, driver, class A output with high impedance speaker directly in output collector or emitter circuit. The standing current would pass through the speaker but probably wouldn't make it sound (much) worse!

Shouldn't be difficult to reverse engineer, there's not that many parts to unravel in the audio end.

[Cobaltblue]

The PCB of Jolly7's Radio looks the same to me as the one in post #14

If you look at the print side of the PCB you can see the holes for the transformers.

2 possibilities spring to mind one is that the manufacturer redesigned the set for transformer less output, the second is that a previous owner did it

Whichever as Herald has said should not be hard to backward engineer

Cheers

Mike T

[paulsherwin]

It does look as if it's been messed around with. If the transformers have indeed been removed it may be better to replace the entire audio section with an LM386.

[crackle]

I agree they look like the same printed circuit with some alterations and some of the audio components missing.
Original chassis on left and the chassis from post #14 on right.

Mike

[Jolly 7]

Many thanks everyone for the suggestions and pictures. The set does appear to be poorly built or maybe was someone's transformerless superhet experiment that didn't work out before it was abandoned. Repairing this radio is not going to be enjoyable because the components are laid out very carelessly. No insulation sleeving has been used and the way the leads have been soldered will make it difficult to desolder and resolder parts. In spite of these issues, I will attempt to fix it at some stage, particularly as I have many LM386Ns which I have used successfully in the past.
My only hope is that the last owner hasn't broken the IFT cores. I don't like replacing them :-(
Will keep you posted.

[60 oldjohn]

Originally Posted by paulsherwin

No switches here, it's a MW only set.

Hi Paul, I was not sure, that is why I said "any" rather than "the" W/C switch.


John.