I realize this does not quite fit the Music part of MMD but I thought
it might overlap enough that someone may be able to help me out. I
was recently given a 'Sound Scriber' (as-labeled) and it records via
microphone on thin plastic disks (7" dia.) in what appears to be a
crude record lathe-type of operation. It also has a conventional
playback arm. I cannot find a date of manufacture anywhere but the
tubes used are 35Z4GT, 35L6GT/G and 12SC7. I would expect these would
put the date of manufacture within some range (I would guess it is from
the 40's). It is a rather compact device, measuring only 13.5 x 9.5 x 9
and has a leather-like covering on the outer surface of the case. I
would very much like to track down a schematic and any other information
for this device in order to attempt a repair (many leaky capacitors,
etc.). If anyone can point me in the direction of someone who
specializes in this type of thing it would be greatly appreciated.
[ My receiving tube manual(s) from that era are in storage at
[ them moment, but I can tell from the tube numbers that this
[ unit operated with its tube filaments strung in series, and most
[ likely had no power transformer. The 35Z4GT would be an "octal"
[ based rectifier tube with a 35 volt filament. The 35L6GT/G would
[ be the power amplifier tube which drives the cutting head. It
[ also has an octal (8 pin, approx 1.25 inch in diameter) socket and
[ operates with a 35 volt filament voltage. The 12SC7 is the
[ preamp tube. I don't remember if that part would be octal or
[ a 9 pin base.
[
[ When I was doing TV service work, I had very good
[ luck replacing leaky paper capacitors with Mylar ones. You
[ can test for leaky capacitors with an ohmmeter, but I prefer
[ an isolated power supply, a current limiting resistor, and
[ a neon bulb, all connected in series. You charge the capacitor
[ in question through the neon bulb, and if the capacitor is leaky
[ the bulb blinks at a rate determined by the leakage current.
[ This can detect very small leakage currents that seem not to
[ show up under the excitation of the battery in your Volt-Ohm
[ Meter.
[
[ There are a number of dealers of used tubes on the 'Net. I'll
[ bet that the 35 volt filament tubes are going to be harder to
[ find than their 6 volt counterparts. Please let us know how
[ you progress with this project. There' plenty of EE's here.
[ -- Jody
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