So audio guru Steve Williams sent me a bunch of pictures of a portable phonograph that he just bought. He collects these old cheap units. It’s kind of like collecting beetles, they are ubiquitous and dumb, but you have to admire their diversity. So Steve has an inordinate fondness for 1960’s vintage portable record players.
He didn’t say where he got it, but eBay is full of such treasures.
Steve wrote us a mock note, acting like he was a young kid that could not understand something this simple.
“Can any or all of you help me to understand the complex subtleties of this device? Note the schematic includes 5 resistors including a variable one, plus 3 capacitors, a little heat sink diode thingie, a motor, a switch, a tube, a transformer, a speaker, and this funny thing that creates electricity when bent back and forth via perturbations in a flat disc rotating beneath the arm thingie that the little crystal generator is located at the end of. Said disc being rotated via the motor through a rubber wheel connected to the table the disc rests on…”
“It’s all too simple to do anything. There must be some magic involved. Where is the software, what is the storage media, what is the underlying code? Where is the D to A converter for that matter?”
Of course, why buy this old precious stuff if you don’t immediately take it apart? Here are the guts of the unit. This is the kind of things my pals bring up with a Variac variable transformer, to try and condition that old paper capacitor. Usually it is these caps that go bad, putting a huge 120Hz ripple in the power supply, which you hear as a horrible hum in the sound.
My pal Eric Shlaepfer restored an old Clough-Brengle oscillograph. Eric doesn’t just replace those old dried-out capacitors with new ones. He takes apart the old capacitors and puts a new one inside, so the restored ocsillograph still looks vintage. Bravo.
And in case you want to see Steve’s record player working, here is a YouTube video of a similar one playing a record.
[Update:] I sent this post to audio guru Steve Williams and he sent back a nice note:
“Thanks for the write up. Only minor correction is that the video on my YouTube channel is of the same player not a similar one. Yes, the cap is weak but the hum is only semi atrocious. Didn’t replace it yet. Put in a very similar NOS Crystal cartridge I had. The album is my very first LP. I sent the mass email and initially only Ron Quan responded. -“
‘It’s a very efficient circuit by using the tube to drop 25 volts AC for the motor winding. The crystal cartridge could deliver at least 0.5 volt AC into the grid of the 25L6. As I recall, these phonographs could play very loud. Of course, the tracking force was in the order of 5 grams or more. Ron’
“Of course Ron meant that the motor drops the other 90 some odd volts leaving 25 for the 25L6 filament in series. (Which AFAIK is _not_ the same as a 6L6 with a different filament voltage.) –Steve”