This is a weird niche project that i've been thinking about for a while. I have a portable record player that works great for multiple speeds, and i've used in in the yard several times to listen to records, but it's kind of a drag to also string out a power cord. 

I also have a wind-up 78 player that works great, but it uses steel needles, which only works with acoustic 78s, those needles are too rough on the later electric recordings. 

The solution: a hybrid, using a spring-powered motor to spin the record and a small electronic amp that can be powered by a battery. Not as convenient as a fully electric rig, but hopefully able to play music for a good amount of time on a battery charge, or until i'm tired of winding up the spring.

The starting point: a (probably 1930s) Phonola portable that i found at an estate sale for $20.

It's complete and the motor probably needs a good cleaning, but it works well enough for some testing and not too nice or rare to modify a bit. Most components are riveted on, which is a hassle, but the dremel can grind them a way pretty quickly.

Next i trolled ebay until i found a tonearm that would be easy to mount and has cartriges available. This one was taken off of a Technics turntable, it's not super fancy but has a nice gimbal mount and i found a cheap 78-specific cartridge that fit the P-mount. Also the straight tube was easy to remove and shorten to fit.

I removed 3", which was probably a little too much, but it works. I made a mount for it to get it in the ballpark of the right height with a record in place.

It would track better if the head weren't angled, but it's going to be wired for mono, so i'm not worried about perfect separation or fidelity. I'll make another mount that's nicer and moves it about 1/4" out so this could also work for 12" disks. 

I'm using amp boards found on Amazon, the output wasn't rated but they take 5-24 volts, which is a handy range for battery power. I ended up needing two boards in series to get enough signal boost, the volume was too low with just one. 

This is my testing setup:

Power is from a DC power supply, and output is going to a guitar cabinet. I also tested a small 4" speaker, which worked, but i probably want something with a wider range. This setup sounded really good, clean signal and good volume range. Everything from 6-24 volts seemed to work equally well as far as the sound.

Lots of work yet to do, but happy that the concept works. For next steps, I'm going to try another preamp board that provides some tone control to compensate for the pre-RIAA sound curve. I also want to see what speaker options i can fit in the case. It needs a proper tonearm mount and plate to mount the volume knob, battery and charging port.