"hatbox" 78 rpm record player
 

Here is an unusual looking 78 rpm record player from probably the late '40's that looks like a hatbox when closed up. I've looked this thing over and can't find any hint as to who made it. At some point, someone replaced the filter capacitors in the amp; but, I plan to give the whole thing a going over. Unfortunately, this is one of those models without a preamp tube; so, I may have to add an extra preamp stage for use with a modern lower output cartridge. The original cartridge is missing; so, I'll probably replace it with either an 89T powerpoint or a Pfanstiehl P51-3.

http://i538.photobucket.com/albums/f...ps283be7d6.jpg


http://i538.photobucket.com/albums/f...ps38035943.jpg

http://i538.photobucket.com/albums/f...psfe54f87f.jpg

That is cool!

I like it.

Thank you for the information and pictures.

Yup....it used one of those huge Astatic crystal carts with metal needles...or if you were fancy sapphire.

According to the date on the 35Y4, mid-1947.
A real novel approach, using the case top, as the turntable. It looks like it was made by a very small concern, as they used machine screws and nuts, to mount the tube sockets and other components.
Hang on to it! Probably VERY RARE!

Wow, radiotvnut sure has a knack for finding the coolest phonos.

What are the tubes in that thing? What does the circuit look like?

Would it be easily possible to replace the rectifier with a
silicon diode and use the tube socket for a preamp tube?

The tubes look like a 35Y4 and a 50A5.


Best to strip the original circuit and move the 50A5 tube to the 35Y4 socket and wire the 50A5 socket for a 14B6 triode preamp tube. Then use a silicon rectifier and replace the voltage dropping resistor with a 420 ohm, 10 watt resistor.

I wonder if there are any loctal rectifier/output combo tube types? There is an octal type 117L7 IIRC that is a power rectifier/output pentode. Something like that would allow a preamp without the dead giveaway of a circuit change that a modern diode would be.

An idea I had is to use a combination triode output tube like a 6bm8, or higher voltage variant of that, with a socket adapter in place of the current output tube.

I was originally thinking of the 70L7 rectifier/output tube and a medium or hi-mu triode. I referred to the 14B6, as it's a loctal based tube.
IIRC, the 70L7 requires a different output transformer, as it's a higher impedence plate load.

I was wrong about the 70L7 plate load. the tube manual shows 2K ohm.
Looks like a good tube for the purpose. :thmbsp:

How about a single FET preamp stage powered by the cathode bias voltage of the output tube? (FET to maintain high input impedance) if you bypass the cathode with a big enough capacitor should be able to get about 8V of pretty clean DC, which would nicely power a single transistor preamp and draw so little current it wouldn't affect the output stage.

Attached image is similar to what I have in mind, not mine, found online, etc, but should be pennies to assemble and do the job nicely without cutting up existing. http://www.till.com/articles/GuitarP...ges/preamp.gif Note: may want to put a bit more filtering on that power supply voltage, maybe a C-R-C filter with say 1000uF - 500 ohms - 1000uf just to keep things super quiet

Thanks for posting that. I'd like to give it a try and see how it works.

On many of these simple circuit players, the motor for the turntable is in series with the tube filaments, and acts as a dropping resistor so the whole filament circuit could be run from 117v.

The majority of the single tube models of the '50's and '60's are that way. The motor is usually 90V and the tube filament is usually 25V; which, adds up to 115V. On models such as this that I've added a preamp tube to, I use a 6AV6 (it's filament has the same current rating as the 25L6 and bumps the total of the series string up to 121V). With today's higher line voltages, it will still work fine this way and even if the line voltage is a little low, it will still work; but, may take a little while longer to warm up.

When solid state models came along, there was often a secondary winding on the motor in order to provide low voltage for powering the amp.