I have a turntable that is a fixed 78rpm speed. Its a Zenith Cobramatic. I was wondering if there is any preferred method to try to slow the speed down to 33&1/3 rpm so I can play my LP's on it.
My methods that I thought of are:

-changing motor for one that I can adjust speed of under the chassis

-finding the gear/chain that drives the wheel and adjusting that somehow

-I heard that zenith made a "topper" that you put on your turntable and it somehow slowed it to 33&1/3. Used bearings or something? I only found 1 sentence from some internet forum about it.

Any suggestions on where to start would be great. I have no real idea on how to proceed with this, or if there is a preferred method?

(Since the zenith model has cartridges, I can change that out to put a needle that works with LP's. It has a 12" setting for the arm, so no problem on using the automatic changer. Just the speed I need worked out.)

Why not just aquire a phonograph designed to play 33's?

I have one that does... but its solid state. I want to use this one for it cause it uses tubes.

I just would like advice on a modification. Not advice on a new unit. : )


Also: Would putting a dimmer in line with the motor be bad/not work? I assume that it woudn't work...

You assume correctly. "Dimming" motors simply starves them of torque. Speed becomes highly erratic.

You could lathe the motor turret to 33. That's about your only speed option.

I'd be highly circumspect of that arm suspension and the underlying mechanism being 'really' compatible with microgroove vinyl.

Why not simply run the leads from the 33-1/3 player's tonearm to the input of the tube amp in your 78 set?
You could use dual RCA jack cables between RCA plugs on each set.

Back in the day there was a requirement to adapt existing expensive consoles to enable them to play new LPs. I don't recall hearing of any practical way to modify an existing changer. Repair technicians had a healthy business swapping out the old 78-only changers for new 3-speed changers.

Maybe you could find a Cobramatic 2-speed changer from the 1948 or 49 model year and install it in your player. It was neat -- had two separate Cobra tone arms.

-David

There was some sort of geared adaptor that sat on the turntable, and was the size of a turntable, that reduced the speed down to 33 rpm.
If I remember correctly, it was like a turntable that sat on the players original turntable, and the record sat on top of this adaptor. I think it might have had a second tonearm attached for playing microgroove records, but Im not sure.
I've only ever seen one once about 5 yrs ago on a now non-existant phono forum when it was for sale on ebay, so no doubt they're a rare item. I cant remember who made it, but it may well have been Zenith.
I guess it was a similar idea as the adaptor that turned your record player into a wire recorder.

Apart from that, all I can say to yafan is ARE YOU MAD?
Why would you destroy what appears to be a nice original Cobramatic just so you can play ABBA or the Beatles through a tube amp?
I mean it's your player & you can paint it green & set it on fire if you like, but it just seems a shame to me.

Couldn't you remove the original turntable and make a plith that sits in the cabinet, and get a small 3 speed turntable like a Garrard Model T, and use it?
At least you wouldn't be making any permanent alterations, and you could drop the original TT back in at anytime in the future if you decided to sell it, or picked up a nice original 3/4 speed machine with a tube amp.

I've not seen one of those adaptors, but then I really pay very little attention to post-war stuff.

RCA Victor offered a replacement turntable with a planetary reduction gear built in to allow the
1931 vintage 33 1/3 RPM (standard groove) "Program Transcription" discs to be played on any Victor Electrola. Some time ago I saw one of these
on an Electrola Hyperion, about the earliest such machine that one could find. So much for Reed and Welch's assertion that RCA Victor never offered a cheap adaptor suitable for use on earlier machines.

I would want the geared adapter above all else, or schematics to one so I can make it myself from scratch. I am looking for a fix that does the minimum amount of change to the unit and if possible make it so that I can take it out/off and have the unit original again.

I've been thinking about a topper mechanism that has a bearing and rubber wheels that would slow the topper somehow while leaving the original stuff alone...

If you had the time, the equipment, and the skill; I suppose this record changer could be slowed down to play LP's. However, there are many nice tube type multi-speed record players that can be bought and restored for a lot less than what it would cost to convert this record changer. Most of the value for this particular model is in the 78 rpm cobra record changer and if it were modified or replaced with something else, it would be worth very little.

Find a Motorola, RCA, Magnavox, Zenith, Philco, etc. hi-fi/stereo console from the '50's-early '60's, restore it, and I think you will be very pleased with the results.

You know, I now dimly recall seeing a Zenith 33 adaptor, but as I recall it ha a separate tone arm for the LP records. Having worked on the 78 only Cobra-Matic I recall that the tone arm is heavy and has more than a little drag, and would be very hard on an LP.

Besides, what ever is there on LP records that is worth listening to, save for the odd re-issue?

These changers do a nice job playing a '40s vintage 78. The tone arm tracks heavy. It has a special mount, socketed, moving vane cartridge with a 3-mil sapphire stylus. 2-mil all speed and 1-mil mono Lp microgroove replacements are available but be prepared to pay up to $40 and they can have age related issues. If the motor shaft was turned down small enough to play 33 1/3 rpm records and the tone arm was lightened so that it doesn’t slice the record to ribbons, you still couldn't play a stereo Lp.

Zenith micro adapter could only play 7-inch records.




This '54 All Speed Cobramatic with neon backlit stroboscope uses a ceramic cartridge. It tracs at about 8-grams and it's still a little hard on the records.

Doug, evert time you post that snazzy Zenith tabletop player I get all excited.
But ya know I'd mod the arm for a stereo cartridge and lighten it up.
I'd have that bitch tracking at 4 grams in no time.

He just posts that to get us excited, building up the desire until the day he decides to sell it. Tricky devil!

You guys convinced me to not alter the phonograph. I'll probably look for one that plays LP's in the future and fix that up.

Maybe you can cut a deal with William and replace your changer with the multi-speed Cobra-matic that he has for sale in the Classifieds.

viewtopic.php?f=15&t=193345

Dave