Minifon P55 wire recorder , pocket size of mid 1950s

better resolution schematic

[...] [...]

I found the rubber drive belt was unobtainable, but eventually came across a substitute by following the route taken by my local postman. For some reason, red G.P.O. rubber bands seem to outlast the ordinary type you can buy in the shops.

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~ Adrian Tuddenham ~
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I can usual fashion-up rubber parts with no problem , rubber tyre, belt and brakes on this all gone west. I was concerned about the plastic from this era. Nothing cracked as far as I can see but I'm aware stress can build up in this sort of plastic and sometimes literally explode to fragments/dust. I was wondering if there was a way of passivating this potential problem or monitoring for it.

I've not heard of any particular problems with these machines, although yours does seem to have had a particularly hard storage life. German plastics were pretty good in that era (self-destructing neoprene came a little later).

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and

this

up

fragments/dust. I

or

I didn't know what sort of plastic. I knew an antiques dealer once and she had a plastic grill on a Dancette or something distintegrate into pieces on moving the cabinet, not touching the grill. I once witnessed an old Thermos vacuum flask cap explode with a surprisingly loud bang when the sun got on it, disintegrated to dust and tiny flakes.

I think I can see the original problem area as someone had loosened a screw in that area . The stop slideway works but the rewind slideway is jammed. The piano key pushes a quadrant arm that pushes the spool-swapping slideway for the drive , the quadrant is not turning but not due to 40 years of rust probably.

Does T on the schematic translate as nano as in nanoFarad and how does A arrow W of the switch posistions translate to play/record or engaged / disengaged or forward/rearward

I've just noticed that the peanut valves are Mullard make , in a German made recorder

[...]

I don't know, I've never managed to get hold of the circuit.

Luckily the machine I borrowed to do some wire transfers had a working amplifier; if it hadn't, I would have done what you propose and brought the head wiring out to a separate amplifier. If you do it that way, you will at least be able to confidently work out the correct time constants from the circuit diagram, rather than guessing at them.

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~ Adrian Tuddenham ~
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I wondr if they were sent over here without valves, so as to avoid an import tax? I believe Grundig were caught many years ago doing something like that and heavily fined.

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made

A bit of a mindslip, I was also looking at some miniature 1 inch display diameter Mullard CRTs also today. The Minifon peanuts were England make but HIVAC. As this is rebadged EMI Emidicta then perhaps the sales tax dodge.

I removed the steel circlip and steel washer , both now replaced without breaking as surface rust only. Circlip holding that quadrant arm in place and now got that slideway working, latching in both senses. To replace the drive band needs the "capstan" cylinder anchor, near that point, removing. Interesting slip clutch inside the steel cylinder , inferred, not seen. One of those spring clutches , freewheels one way and low take-up of torque the other way.

I think some manufacturers sent stuff into England without the valves, so it wasn't a working piece of equipment. Then, when they put the valves in and tested it, they could claim it was "Made in England"; so they didn't pay luxury import tax (or whatever the tax was at the time).

My recollection is that only one bearing needs to be removed to put a new drive belt on the capstan drive cylinder - and it was the opposite one from the one I first removed.

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~ Adrian Tuddenham ~
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German

but

dodge.

place

the

removing.

One

the

I'm starting to find differences from this schematic

orientation of triple ganged master switch is different I cannot find the fast acting switch parallel to the seriesed end or reel switches

[...]

The first place I would look is around the operating key bank. I assume it momentarily by-passes the end-of-spool switches, so it is probably operated from one end of the slide locking bar on the key bank.

Have you tried following the end-of-spool wires back from the deck plate onto the amplifier board (if they haven't fallen off yet) ? They might lead you to it.

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~ Adrian Tuddenham ~
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reel

I can see why the 2 end of reel switches are in series but not why that "switch" is in parallel with another one , the fast acting one, as it will do nothing unless at the end of reel , which has to act before the fast one , so what is the point?

I haven't got the machine in front of me, but my guess is:

At end of reel, the motor is disconnected and then cannot run either way. Pressing a button will operate the slide bar and momentarily re-connect the motor for long enough to get the wire moving and re-close the limit switch circuit.

It could have been done much more elaborately, so that each direction button operated in association with the appropriate limit switch; but that would have involved more wires from the deck to the chassis and extra switches on the button bank.

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assume

plate

might

will

one

So a mistranslation, for "fast acting" read short duration momentary on. There is some sort of leaf switch under the master sw bank although I cannot see any wire to it without removing the master sw. This is activated by the stop slideway. Indeed, should a reel stop, with the end of wire spring-out lever touching an end sensing switch then the motor would be locked out without such a fudge or manually turning the spool. Presumably p19 of the user manual about the red light coming on at end of spool

That would be my assumption.

It sounds as though you have found it.

I haven't got the manual, but I do remember a light coming on at the end of the wire when the motor stopped.

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user manual

it says , for wire breaks, just knot the ends together, I may try stretched PTFE spaghetti tube for butt joints of the wire breaks, if interesting contents.

technical details and pics of a museum grade one

schematic

Thanks, that could come in useful.

That is the standard way with all wire recordings. Most of the standard systems run around 20 ips, so the duration of signal dropout due to the amount of wire in the knot and the loss of head contact is not terribly significant.

I have had to recover the sound from wire recordings of gaelic, which become tangled and then the bits edited back in the wrong order (some backwards). Now THAT was fun!

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~ Adrian Tuddenham ~
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Low heat and stretching reduced 1mm outside diameter ptfe tubing down to .5mm diameter. Easily passes alonwire-sense through the eyes of the tape-head. Hopefully superglue would have enough binding with the ptfe and recording wire to make a joint.