Unique Transitional Radio

[Ed_Chambley]

Just thought I would share a restoration I recently completed.  This is a 1949 Zenith Dual Cobramatic.  I got this for free and it lived outside for a couple of months, so I had to replace the top laminate.  Since I did not have any of the parts that deteriorate, I changed a coupled of things.  First, it had a grid bias 6K6 which is now a K bias 6V6.  Used a Hepner Alnico from a Hammond Tone Cab and gave it a better OT to attain a better frequency response.  It has a crossover and an additional ribbon tweeter.

Added Bluetooth receiver running off a regulated 5V from the Rectifier and completely reworked all the finish.

I hope you guys like it.  This was right at the changeover from Mono 78 rpm to stereo LP and has FM and of course AM. Now everything works and it will put out a very nice clean 5 watts.

[Ed_Chambley]

Another

[Ed_Chambley]

More

[Ed_Chambley]

Again

[Ed_Chambley]

Really?

[Ed_Chambley]

I know you are bored by now, so this is the last of many I have.  I always forget to take the gut shot of the inside, but rest assured it is no longer a rats nest and doesn't use the chassis as part of the heaters anymore.

This is very unusual for me as I really only collect original radio, but this one is sort of rare and to me is historically significant being the cornerstone of the beginning of the changes in music listening.  Plus having the Dual arms on the same side is very different.  Usually the dealer add the green arm, the 78 to the back.

[Ed_Chambley]

Well one more so you will know what I mean by the green arm.

[Ritchie200]

Too Cool!  Old and new, that is fantastic.  Had you not given it a home it would probably be in pieces in some land fill.

Well done, young man!
Jim

[shooter]

Very Nice!

I will be looking into Bluetooth for my current KT88 PA, any insight would be welcome!

[PRR]

> a 1949 ... right at the changeover from Mono 78 rpm to stereo LP and has FM

LP, not "stereo LP" which was another 8-10 years up the road.

Changeover was slow. 1952, 78 was still half the total sales, and a larger proportion of Elvis' early sales.

The FM is super-deluxe for the time, a time of chaos because the FCC changed the frequency band from what had been assigned.

[Ed_Chambley]

> a 1949 ... right at the changeover from Mono 78 rpm to stereo LP and has FM

LP, not "stereo LP" which was another 8-10 years up the road.

Changeover was slow. 1952, 78 was still half the total sales, and a larger proportion of Elvis' early sales.

The FM is super-deluxe for the time, a time of chaos because the FCC changed the frequency band from what had been assigned.

OOPS, you are so correct.  I did not mean stereo, however I do have a quadraphonic system and 2 whole albums recorded in quadraphonic.

[Ed_Chambley]

Very Nice!

I will be looking into Bluetooth for my current KT88 PA, any insight would be welcome!

Easy.  I simply purchased a bluetooth receiver module of $6 on amazon.  The kind that plugs into a aux jack in a car.  Took that thing apart as they have regulators inside and used some stranded 24 to connect to the rectifier wires from the PT.

You will have to keep it in connection mode, but it works great.  To keep in connection mode, I removed the button switch and added a jumper.  I have a schematic to make one and they are also all over the web.  The total parts from Mouser to make one was $19 and I still had to pay shipping and put it together.

Just make sure the BT receiver you buy shows the power cord.  If the cord is only a usb cable then it will be a regulated receiver.  Sometimes cheap and ready beats DIY.  You can ignore the buttons that are up and down.

[Ed_Chambley]

Too Cool!  Old and new, that is fantastic.  Had you not given it a home it would probably be in pieces in some land fill.

Well done, young man!
Jim

Thanks Jimbob!  You are correct, I got it because the guy who had it was too lazy to tote it off.  I actually saw it on the edge of his front porch sitting where rain would hit the top.  He was outside and I stopped and asked if I could look at it and he said only if I took it.

Neat thing is all the knobs were there and the doors were closed which saved the chassis and turntable.  I am really into Tombstone radios mainly with a couple of Giants.  I say a couple.  One day I will quit buying the darn things, but I love them for some silly reason.

[Ed_Chambley]

BTW, if you notice the plug that goes to the turntable is not plugged in.  On the other end of these things is a receptacle for the turntable which has an exterior ground connected to a shielded cable which should, I said should make a ground.  If you ever mess with any of these things, DO NOT plug the thing in unless you have insured continuity from the pin at the amp and the shield wire.  Most, everyone I have ever worked on no longer have a proper ground and the turntable WILL shock you.

I did not complete it before the photos, but what I do is add an 16 awg stranded from the ground pin back to the female connector and solder it to the outside replacing the shielded ground wire and then use automotive loom to wrap it together.

Want to know how I found out?

2 hands, one on each side of the album or LP.  Placed record on turntable and rested left hand on unpainted speed switch and right hand lifted the arm and ring finger decided to wrap itself around the stand for the tone arm.  I say wrapped because electricity tends to do that.

It is ONLY wall voltage, right?  Well I let her go and it was not that bad really, not as bad as when I caught a bassman chassis from  hitting the floor.  Problem here was it was on and my left thumb was right on top of the rectifier tube.  Just a reaction.  After this little experiment I upped my safety game a LOT.

Now I refuse to work on an open chassis without an amp stand clamped to my work table and the amp bolted to the stand.  May be overkill, but I do not think so anymore.

[shooter]

May be overkill, but I do not think so anymore.

way better than justkill

thanks for the BT tips

[DummyLoad]

nice restoration ed. beautiful work.


--pete

[Ed_Chambley]

nice restoration ed. beautiful work.


--pete

Thanks Pete.