1956 Zenith Cobra-Matic Stroboscope Changer Transition

[Hi-Fi-Mogul]

Bill: Thanks for the support, but read on ha ha !

Chris: The noise level of this vertical idler is as much
as a regular idler wheel in a V-M.

The speed per the strobe is not overly stable.

I may or may not do the adjustment that might make
it better.

Overall, these Cobramatics I now find are over engineered to do
some simple cycling functions.


One last fly in the ointment.

I installed a new cartridge, and it is working intermittently
and sometimes distorted.

I put the old cart in, and it plays OK.

I determined the metal bar contacts on the new
cart are not as thick as the old ones.

I had already cleaned the contacts in the cart's mount.

I tweaked a piece of aluminum foil b/t the cart and mount
and the cart worked fine.

But, the foil is not a permanent fix at all.

I looked at the donor Cobra tonearm which actually has
1/2 inch mount posts.

I found an EV-26 stereo cart that I will test today.

So, if that all works out, I have to once again remove the
old arm, run new wiring, and install replacement arm/cartridge.

I will add these Cobramatics to my "won't do" list.

[William]

I'm sorry, Mr. Mogul, that this one has been such a pain, but what else to you have to do and just think of the learning experience you are getting.

Bill

[Hi-Fi-Mogul]

Tested the EV-26, two stereo leads and common
ground all good.

Removed old tonearm, ran 3 tonearm wires through
changer wiring channels using guide wire.

Ran wires into replacement tonearm. Soldered both stereo leads
and common ground onto audio plug to amp. (Stereo to mono amp)

Attached wire clips to EV-26, then attached cart to tonearm.

Cussed while I tried to re-attach tonearm to its swivel mount.

Cart output excellent playing Roy Orbison.

Need to tweak end of record tonearm pickup position.

Picking up on second to last song.

I wish I could just leave it on the bench, working...ha ha !!!

[William]

Good work, and it will be just fine. Famous last words, right!

Bill

[Hi-Fi-Mogul]

Good work, and it will be just fine. Famous last words, right!
Bill

Well Bill, you hit it. One last problem, again ! Ha !

I replaced the record support arm as getting ready for final
test with a record on the spindle.

Ready, set, no go.

The record won't drop. Spindle workings are moving, but
something's awry there.

I actually have an early 1950's Cobra radio/phono table top set.

I looked at its spindle, and noticed it moved in ways this one
does not.

I'm hoping that tomorrow I will discover it just needs more
cleaning.

At the worst, the owner can manually place a record on the
platter, and initiate the play sequence.

Man, this is turning into a hi-fi repair saga.

[electra225]

That's what we are here for. Thanks for sharing, Mr. Mogul.....

[Hi-Fi-Mogul]

I am done with this changer.

I got the inside spindle piece set in the right
vertical orientation.

It was dropping records, then it would not.

Then it stalled a bit, and dropped the record late
onto the tonearm and busted the stylus.

The owner will have to manually place a record over
the spindle onto the platter and then engage the
auto play.

I have tried everything on that spindle, so
my final diagnosis is that the inside piece is worn
out just enough to not seat the record properly.

Yeah, I learned a lot about these, but I'm not
going to take on another.

l am ready to get this all back in the cabinet and outta here !

[William]

And here I was going to see if you wanted to work on 6 more of them. There is a record shop in a neighboring town that has 6 vintage Zenith console all with the changer you were working on. He thinks they are something special and every one of them needs a complete overhaul both changer and electronics. He also has a Pilot console that he wants two grand for. It needs 3 of everything including the cabinet. On the plus side, he probably has over 10,000 records to sell, and most are reasonable priced.

Bill

[electra225]

Great job, Mr. Mogul. I haven't commented on your project much, because I didn't have anything beneficial to add. I appreciate your taking the time to document the project and share it with the forum. I have six Collaro changers and a pickup load of VM's that need to be gone thru. The only one I have that works right is the one in the little Magnavox record player I did the Tolex on. Bill went thru that changer before I got it. That thing changes 45's all day long. Perfect every time.

[Hi-Fi-Mogul]

Bill, that's pretty humorous about those "gold plated" Cobras !
It is nice that the records' prices are reasonable.

Greg,
You helped me with the transformer/electromagnetic
trouble-shoot, remember ?

And if shipping were cheap, I'd be happy to get at least
several of your Collaros and V-Ms working again.

[Hi-Fi-Mogul]

The AC power wires on the female plug all broke off
just now.

I guess I'm glad it happened while the Zenith is still here.

It is a pain trying to push the wire retainer plugs through
the plastic plug holes.

The wires were really eaten up with that green goo.

[Hi-Fi-Mogul]

I was able to push out the power plug connectors,
from the rear of the plug.

They are held in with tabs that can be bent out from
the metal connector's body.

There was a lot of green crud in all of the holes of
the plastic plug that made pushing the connectors
difficult.

I cut three 12 inch lengths of 20 g stranded wire to
solder onto the metal connector pins.

I tinned a small area of the bare wires right where
the wiring insulation starts, so it
would serve as a stable anchor for bending the
end of the wires through the connector's eye hole
and onto the connector arm.

The wires now go through the plastic connector's
holes easily.
I'll bend out the tabs on the connector pins and
carefully push the pins into the plastic connector body.

Then put a piece of shrink wrap over the wires, solder them
onto the original power wires, and shrink wrap the solder joints.

[William]

Looks good Mr. Mogul and I will keep my fingers crossed that this is the last thing you will deal with.

Bill

[Hi-Fi-Mogul]

Thanks Bill.

I didn't like the feel of the plug.
After attaching it to the pin plug,
I glued it in place.
I soldered blade connectors to the
new wire extensions and the old wires.

Electrical tape over the blade connectors and
Ms. Zenith has gone back to her home.

[William]

Congrats, and enjoy that pizza and beer.

Bill

[JoshDenty]

Hey! Sorry to revive a dead thread. I'm looking for some information on the tone arm on the unit you all were discussing. It's extremely unique and I happen to be working with the same one.

I've got a Zenith Cobramatic with the same stroboscope turntable in this thread that I'm gathering parts for. A previous owner seems to have replaced the original cartridge with a modern Tetrad style. It works, but I've decided to try and return it to a factory original style. Problem is, the conversion also means that it no longer has the original switch or connector to hold the appropriate cobra cartridge.

Hi-Fi-Mogul - is there any chance you're still in contact with the owner of the turntable you were discussing here, or do you have any photos of the switch and mounting hardware for the cartridge? I'm trying to get my hands on some reference images and measurements so I can reproduce the part for my unit.

Any help is appreciated. Thanks!

[TC Chris]

Did that use a standard crystal or ceramic cartridge, or Zenith's "Radionic" system? In the latter, the cartridge had a moving vane that modulated an RF signal, then was demodulated by the "preamplifier." I have a 1948 Wurlitzer 1100 that uses a Cobra arm (prominently labeled) and the Radionic system. I have assumed that it allowed a lower moving mass and higher compliance for lower record wear and longer stylus life, which would be useful in jukebox service.

Chris Campbell

[JoshDenty]

I'm not sure. I keep seeing the radionic/ceramic switchover date as 1954, but my unit clearly has a 1953 build date on it and doesn't seem to have the extra oscillator tube needed to drive a radionic cartridge. It's not been modified either, save for the mounting hardware, the tube layout sticker is still on there and it matches a standard 3 tube amp most of these types of units have. I suppose it must be ceramic.

The good news - I've managed to source a parts turntable that has all the missing parts I need, including the cartridge. I'm not going to delude myself into thinking it's still good, but with a physical reference I can at least work something out to get my unit going in its original configuration.

Given that I've got a full turntable and all I need to pull is the tone arm - to my knowledge, anyway - that means I've got a complete mechanism worth of spare parts, if anyone needs anything. Also happy to provide reference photos to build reproductions now or in the future. Once I get my unit going I should be able to part out the rest if someone needs something to get theirs going.

[JoshDenty]

Just wanted to pose an updated, since Hi-Fi-Mogul had asked for references and whatnot. I'm still tearing into the parts table to get the tonearm off, but I have learned that the correct cartridge for this model is a Pfanstiehl 992, which is still readily available from VM Audio Enthusiasts. I paid around $22 for the variant with a diamond LP needle and sapphire 78 needle. I guess it's the radionic cartridges that are hard to find.

I am sacrificing stereo compliance to use this cartridge, but given the unusual variant I'm working with I'm ok with that. Once I get my unit working I'll check to see if this thing can handle stereo at all.

[William]

Thanks for the update, Josh. If you can get a stereo cartridge to fit in that tone arm it will probably play stereo records. Tone arm weight might be an issue, I am not sure how that would be adjusted on your changer.

Bill