67.5v DC power supply??

[Sammas]

Hello brain trust!

I got my hands on a little EMI L2B portable field recorder from the 1950's that i would like to get up and running. It is all valve, 1/4" running at 7.5" per second. It is battery powered, using 8 'D' size cells plus a big old Eveready 457/467 67.5v battery.

One lot powers the transport, the other powers the valve goodies inside... but the bad news is, $80 worth of batteries only lasts an 1.5 hours or so... perhaps a bit longer with you rewind via the hand crank.

Any suggestions on powering this little thing via a DC power supply? I have attached a schematic.

 

[RuudNL]

As far as I can see the machine uses 4 batteries: 3V (filaments), 6V (motor) and two 67,5 batteries connected in series (BY2 and BY3) for the anode voltage of 135 V.
The 3V and 6V should be no problem; a transformer, rectifier an buffer elco followed by an voltage regulator will do the job.
First you should get an idea of the current and select the transformer and regulator accordingly.
I suppose the HT will not draw too much current, since there is no output stage delivering any power.
So a transformer, rectifier and C-R-C filter may be adequate. The voltage is not very critical, since the battery voltage would not be very stable either.

 

[PRR]

That's a RadioMuseum schematic. At sign-up, RadioMuseum members promise not to distribute RM images. The downloader name is water-marked on the image. I would prefer you take it down.

The 135V demand: V3 and V4 may be pulling 6mA each. V7 probably 1mA. The other four can't be 100uA each. So 13mA total. This would be a moderate load on a 15-stack of 9V batteries. Find a couple bargain-packs of 9V batts; even at the price, this has to be cheaper in short-run.

The filaments are 3V @ 0.050A and 1.4V @ 0.050A. The wiring is a maze but I figure about 0.250 Amps @ 3V. This is entirely within reason for two D-cells.

The motor is totally unknown. Since it is made for D-cells, start with that. Make a sandwich of copper, cardboard, copper, slip it in the end contact, measure the motor current.

If you use it as a tape deck you are unlikely to use it many hours (tape is obsolete). Batteries will buy your fun, and cheaper than nose-candy or sports-cars (perhaps cheaper than the tape you eat). If you use it as a funky mike amp, you don't need the motor power, and again batteries are not a deal-breaker. If you wind up using it in a 24/7 radio operation, you will find a way to wall-power it, without hum/buzz.