Minifon P55 wire recorder , pocket size of mid 1950s

[N_Cook]

Anyone aware of any pitfalls for the unwary renovator? Its been in an
English garden shed for 40 years. But all mechanicals seem to be ok
,despite patchy rust and grime. Spool bearings and sprung tri-ball retainers
function, "winch-winding" head up and down mechanism works, motor turns by
hand, "capstan" cylinder rotates, and deck slides across on piano key
activation.
All rubber parts perished. One electrolytic has its aluminium case corroded
to dust.
I intend getting just the mechanicals in working order , hook the play head
up to a modern tape recorder amplifier to hear what is on the wire drums,
before looking at the electronics proper. All 3 peanut valves and all the
rest of the electronics seem to be present. At least the previous owner
removed and discarded the 3 batteries 40 years ago.
There is one brand new Protona set of spools with security tape around the
outside of its case but also yellow thread with Protona logo stamped lead
seal on this thread linking the spools. What is that security aspect about ,
I cannot find a www reference to that.

much prettier looking one
http://vintage-technics.ru/Eng-Minifon_P55.htm
anyone know of a www higher resolution version of the schematic on the last
of the second page?

user manual
http://www.cryptomuseum.com/covert/minifon/p55/files/p55_manual.pdf

 

[N_Cook]

better resolution schematic
http://vintage-technics.ru/Minifon P55/1/Scanned-P55-1.JPG

 

[Adrian Tuddenham]

[...]

All rubber parts perished.

[...]

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.

 

[N_Cook]

[...]

All rubber parts perished.

[...]

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.

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.

 

[Adrian Tuddenham]

[...]

All rubber parts perished.

[...]

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.

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).

 

[N_Cook]

[...]
All rubber parts perished.
[...]

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.

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).

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

 

[N_Cook]

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

 

[Adrian Tuddenham]

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

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.

 

[Adrian Tuddenham]

[...]

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 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.

 

[N_Cook]

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.

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.

 

[Adrian Tuddenham]

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 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).

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.

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.

 

[N_Cook]

dodge.

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.

I'm starting to find differences from this schematic
http://vintage-technics.ru/Minifon P55/1/Scanned-P55-1.JPG
orientation of triple ganged master switch is different
I cannot find the fast acting switch parallel to the seriesed end or reel
switches

 

[Adrian Tuddenham]

[...]

I'm starting to find differences from this schematic
http://vintage-technics.ru/Minifon P55/1/Scanned-P55-1.JPG
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.

 

[N_Cook]

[...]

I'm starting to find differences from this schematic
http://vintage-technics.ru/Minifon P55/1/Scanned-P55-1.JPG
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.

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?

 

[Adrian Tuddenham]

[...]

I'm starting to find differences from this schematic
http://vintage-technics.ru/Minifon P55/1/Scanned-P55-1.JPG
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.

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.

 

[N_Cook]

[...]

I'm starting to find differences from this schematic
http://vintage-technics.ru/Minifon P55/1/Scanned-P55-1.JPG
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.

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.

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

 

[Adrian Tuddenham]

[...]

I'm starting to find differences from this schematic
http://vintage-technics.ru/Minifon P55/1/Scanned-P55-1.JPG
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.

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.

So a mistranslation, for "fast acting" read short duration momentary on.

That would be my assumption.

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.

It sounds as though you have found it.

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

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

 

[N_Cook]

user manual
http://www.cryptomuseum.com/covert/minifon/p55/files/p55_manual.pdf
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
http://vintage-technics.ru/Eng-Minifon_P55.htm

schematic
http://vintage-technics.ru/Minifon P55/1/Scanned-P55-1.JPG

 

[Adrian Tuddenham]

user manual
http://www.cryptomuseum.com/covert/minifon/p55/files/p55_manual.pdf

Thanks, that could come in useful.

it says , for wire breaks, just knot the ends together,

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!

 

[N_Cook]

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!

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.