Zenith Cobra record player

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Zenith Cobra record player

Post by Wildcat445 on Sun May 10, 2015 10:13 pm

A friend of mine brought over an old Zenith radio/ record player for me "to take a look at."  I looked at it.  It has a Radionic cartridge.  Nothing worked.  The radio made noise from the speaker, but that was it.  No output from the cartridge.  Goody.  The turntable does not  turn.  The motor is seized tight.  

Further tinkering revealed that the radio will somewhat work, bringing in a couple stations weakly.  No hum, though.  I decided to clean the controls to see if that would make any difference.  After I cleaned the radio-phono switch, and if I held it in just the right spot, I could get output from the cartridge.  My next step is to recap the chassis, check resistors, check the tubes and thoroughly service the changer.  And investigate the function switch more thoroughly.  This is my first foray into the world of Zenith Radionic players, so here we go.  I believe this to be a model J-661R.  This is subject to revision later.  I'd be happy to take some pictures if anyone is interested.

WC


Last edited by Wildcat445 on Tue May 12, 2015 4:50 pm; edited 1 time in total

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Re: Zenith Cobra record player

Post by Bill Cahill on Sun May 10, 2015 11:22 pm

What is a radionics???

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Re: Zenith Cobra record player

Post by Wildcat445 on Sun May 10, 2015 11:52 pm

That is a cartridge that develops an RF signal and send it to an amplifier that turns the RF signal into an audio one. Not that I'm an expert, you understand, but that is how it has been explained to me. All I know is that you don't troubleshoot them by putting your finger on the cartridge wires and listening for a hum. It's almost as silly a setup as the Philco Beam of Light system from the 1940's. If I can get this one working, I will have learned something. Tony V. is the Zenith expert, so perhaps he can bail me out here if I've explained something wrong. I have no idea what I'm doing, I'll just admit that from jump street. From what I've seen thus far, they are not horribly complicated. But I don't have it back with its owner yet. I know, I know, I don't work on other people's stuff. When am I ever gonna learn?

WC

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Re: Zenith Cobra record player

Post by Tony V on Mon May 11, 2015 12:46 am

Your right on WC about the cartridge. They almost never fail so your plan about recapping the chassis first also checking the osc. tube is right on par with what I would do. It sounds like you might have to do some more cleaning on the switch also. I'm no expert but I do have several of these under my belt already. Pictures would be appreciated also.
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Re: Zenith Cobra record player

Post by Bill Cahill on Mon May 11, 2015 9:47 am

Nrever heard it called that name before. We just knew them as the models with phono oscillator. They work pretty good, but, are tricky, and, may need readjustment after rebuilding.
Last one I had was twenty five years ago.

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Re: Zenith Cobra record player

Post by Wildcat445 on Mon May 11, 2015 9:52 am

Thanks, Tony. I can't get back to it for a couple days (mowing) but I may be on the right track. That thread I told you about is where I read a comment about Radionic cartridges being pretty reliable. I was just gomming around when I decided to clean the controls. Are the power switches on the changers generally reliable? The motor has an issue, but I need to make sure I have power as well. This player is in fairly nice condition. I will try to get some pictures.

WC

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Re: Zenith Cobra record player

Post by Wildcat445 on Tue May 12, 2015 4:58 pm

I got in some tinkering time this afternoon, so I thought I'd share what I found. I have taken some photos and will share those as soon as I can get them onto my computer and then here.

The chassis has some black beauties in it, so I will CAREFULLY remove those for the guitar amp guys to use. The turntable motor was stuck, so I removed it, took it all apart and got it turning again. A generous drink of turbine oil should take care of that. The motor mounts were still in good shape and pliable. The drive system is different than what is typically seen. The motor shaft turns a wheel about three inches in diameter, which in turn drives another little wheel at right angles of the first one. That little wheel contacts the underside of the platter, causing the platter to rotate. To change speeds, the little wheel changes its travel on the big wheel and the platter. This causes the change in speeds. Rather ingenious. Terribly simple if everything is in good condition and free of oil and dirt. I believe the reject mechanism to be stuck somehow. Something turns really hard and the tone arm cycles again and again. I'm going to have to dig deeper to get this back in shape. There is a wire on the motor that is flapping in the breeze and will need put back where it belongs.

WC

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Re: Zenith Cobra record player

Post by Wildcat445 on Tue May 12, 2015 6:11 pm

The model number MIGHT be H-661-R.  I can't find a "J" in Riders, so we'll call it an "H" for right now.  I can't read the number on the back and the one on the chassis is smudged.  So I'm guessing, not that it really matters.  The chassis layout and tube complement matches the "H".

I have this player playing.  I still have a hum, so I need to finish the caps and change out the filter caps.  The tubes are all okay.  The 35W4 and the 50C5 are GE's with the other four being original Zenith.  I have Zenith tubes to replace the GE's so I'll do that.  This is actually a pretty good record player, with tons of volume and a pretty good tone for having basically a table radio chassis.  I finally got the function switch clean enough for it to work dependably.  I will also admit to adding a spritz of WD-40 to the switch.  The same for the other controls and the tuning cap.  A good recap and resistor check should put this little set back in the pink.

Incidentally, for those of you who may not have seen one of these turntables work, the drive system in this thing is not only unique, but also ingenious.  You can essentially adjust the speed if the record runs too fast or too slow.  There are no "clicks" on the speed control, but a continuous sliding control.  I'm impressed.  This turntable has a General Industries two-pole motor.  The upper bearing on this motor was the problem.  At first blush, the turntable looks rather puny.  It is actually pretty well built.  The rubber is still soft and pliable, odd for a 60+ year old record player.  I can't find evidence that it has been messed with much.  

I don't typically go out of my way to acquire anything made by Zenith, but I may have to have one of these Cobra Radionic record players. This thing sounds almost as good as one with a GE Variable-reluctance cartridge. I'd probably look for a console so I'd get a better chassis and larger speaker, but I would not turn down one like this.

WC

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Re: Zenith Cobra record player

Post by 75X11 on Tue May 12, 2015 7:07 pm

Wish you could put up a pic or two for posterity. And to see what it looks like. Very Happy
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Re: Zenith Cobra record player

Post by Tony V on Tue May 12, 2015 8:52 pm

WC...now you see why I like them. They're easy to work on and the sound isn't too shabby.
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Re: Zenith Cobra record player

Post by Wildcat445 on Wed May 13, 2015 1:05 am

They look really complicated when you first see one.  They are actually simplicity personified.  Just a motor driving a big wheel, it turns a little wheel, and it turns the platter.  With an infinite speed control.  I'm not sure I'm a fan of the "floating" tone arm, but it seems to work okay.  I would be more comfortable with a tone arm rest of some kind.  The sound was what impressed me.  With a 50C5 output tube and a 5" speaker, I expected it to sound like a clock radio.  The sound belies the electronics certainly.  75, I have some pictures taken.  I want to take better, more focused picture of the drive system.  I'll get them on here ASAP, promise.  

Tony, had I not read a comment you made on "that other forum" about one of these, I would not have tackled this one.  I really want to thank you for your help.  I definitely learned something. And I see why you like them. There are lots of the console versions floating around this area, usually for cheap. Like a 12H-090 and those models. I personally do not care for the styling of them, but I'll bet the sound is impressive if it is anything like this one.

WC

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Re: Zenith Cobra record player

Post by Wildcat445 on Wed May 13, 2015 4:23 pm

Some pictures of this little player.  First, the victim as it appeared on my bench.



The bottom side.  I don't see any evidence that there was ever a cover on the bottom.  It sure needs one.



The "business end" the turntable.  The tone arm just flops in the breeze, but it seems to work just fine.



Notice the little white button to the extreme right edge of the turntable.  That button operates a solenoid-operated reject mechanism.  Really slick and VERY cool!  This picture is of the chassis.  Your basic AA5 radio chassis with a 12J5 oscillator hanging off the rear edge of the chassis.  Not a lot of R&D put into the conversion.



The front side of the chassis.  That little speaker sure works hard and puts out a surprisingly pleasant sound.



The motor on the turntable.  This is while I am taking it out to get it running again.  As they say in the tractor hobby, it was "light stuck."



The motor mounts were in great shape for being 60+ years old as far as I know.



These two wheels are driven by the shaft on the motor.  This drive is an infinitely variable speed setup.  This device definitely cures the age-old problem of older record players having incorrect speed.



This shows how the little wheel drives the platter.  I was impressed with how this worked.  Extremely simple.



Finally, playing a record. A Patti Page record, "Would I Love You."



WC



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Re: Zenith Cobra record player

Post by Bill Cahill on Wed May 13, 2015 4:35 pm

I used to have that model. That's a replacement changer. The one mine had was 78 rpm only. It's from the fourties. But, they're not overly valuable, so, as long as it's not hacked up, the mid 50's four speed changer is fine.

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Re: Zenith Cobra record player

Post by 75X11 on Wed May 13, 2015 4:55 pm

Very nice pics! They always make good references.
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Re: Zenith Cobra record player

Post by Wildcat445 on Wed May 13, 2015 5:15 pm

I'm not certain of the age of this record player. The service schematic was dated 1954. The changer in this player appears to be original. With the exception of a couple tubes, everything else looks like it was never messed with. It works well, my friend is delighted, I learned something and had a ball going thru it. It was a win-win all the way around. Thanks, 75. Very Happy

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Re: Zenith Cobra record player

Post by Bill Cahill on Wed May 13, 2015 5:42 pm

Service schematics wre often printed several years later. Yes, they are a good sounding set.

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Re: Zenith Cobra record player

Post by Tony V on Wed May 13, 2015 8:16 pm

I also have that model and that IS the original changer for it. It was my grandfathers and know it was never doctored with. Early 50's sounds correct for this model. I'm glad you had fun with it WC and it looks like you got a nice example to be your first Zenith Cobra-matic to work on.
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Re: Zenith Cobra record player

Post by 75X11 on Wed May 13, 2015 8:25 pm

I was wondering, looking at the settings on it, do any of you have any of the 16 rpm mobile microgroove records ?
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Re: Zenith Cobra record player

Post by Tony V on Wed May 13, 2015 8:34 pm

I have a few but they don't play well on the cobra because of the size of the stylus tip on the needle. Tip sizes for the cobra were 1 mil for 33's and 45's...2 mil universal for all speeds (but this one didn't work well either) and a 3 mil for 78's. The 16rpm records had a smaller groove than 1 mil more like a .7 mil like you find in stereo records so any of the stylus' mentioned above would have been too fat to track on a 16rpm record. They will play with a 1 mil but tend to skip and distort.
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Re: Zenith Cobra record player

Post by 75X11 on Wed May 13, 2015 8:59 pm

I had heard they were quite fine even by LP standards. It's a wonder to me they could make them work.
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Re: Zenith Cobra record player

Post by Wildcat445 on Thu May 14, 2015 1:04 am

There are Zenith consoles with Cobra-matic changers in them in every antique store from here to Milwaukee and more advertised on Craigslist.  I have been avoiding them because I personally find them ugly, and I had heard "stories" about the Cobra-matic changer with the Radionic cartridge and how difficult they are to work on.  No that the myths have been disproven, I may try to find a nice one and go thru it.  Those changers are really slick.  And the electric reject solenoid is over the top.  Not something you would expect on a small record player with an AA5 chassis.  The credit on this one belongs to Tony.  Had I not read his comments, I may not have attempted this one.  I had a ball, so thank you Tony!  Very Happy

I know what I was forgetting. Can the needle be changed or do I have to replace the cartridge when the time comes? From what I can see and hear, it seems fine for now.

WC

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Re: Zenith Cobra record player

Post by Bill Cahill on Thu May 14, 2015 10:01 am

The entire cartridge has to be changed. They sometimes show up on ebay.

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Re: Zenith Cobra record player

Post by Bill Cahill on Thu May 14, 2015 10:03 am

Green is 78. Red is the other two speeds. If it is a white turnover, that has both needles. Stereo Needle guy should have them.

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Re: Zenith Cobra record player

Post by Wildcat445 on Thu May 14, 2015 10:24 am

Thanks, Bill. I think this one has the red cartridge.

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Re: Zenith Cobra record player

Post by Tony V on Thu May 14, 2015 2:36 pm

Red (3mil) is for 78rpm....Red/green (2mil) is all speeds but not recommended as its stylus is too fat for 33 and 45's and too thin for 78's...Green (1mil) is for 33 and 45 mono recorded records. The white needle goes in the later cobra-matic's with the rocker switch built into the head to select. The ones like you have, you switch the whole cartridge/needle assembly as they're all in one.
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