ZENITH C-519 clock radio (American set) - UK Vintage Radio Repair and Restoration Discussion Forum

stephanie · 31st Oct 2005, 7:09 pm

Wow. Seems like I'm just cranking these ******* out recently.

Note: Picture is "borrowed".

http://radioatticarchives.com/images...-519_Shinn.jpg

This one was a project I was fighting with for the better part of a year.

This Zenith dates from around 1963 and uses a conventional American 5-tube series-string circuit (12AV6 detector, 12BA6 IF amp, 50C5 audio out, 35W4 rectifier, 12BE6 converter). It runs off 120 volts AC only, however because of the clock motor. If this motor were taken out of the equation, the radio would be perfectly happy on 120 volts DC.

I picked it up for a tenner (American dollars) at a swap meet back in 2003 and sat around until earlier this year when I finally got to it.

When obtained, the set was faintly picking up some stations. The volume control was frozen in place and the tuning mechanism also suffered from crusty grease.

There were two wax paper capacitors to be replaced under the chassis plus the mains filter.

A bit of contact cleaner and a drop of lightweight sewing-machine oil unstuck the volume pot and while messing around under the chassis, I also managed to break the already rotten tuning drive string.

This was replaced with "fly fishing line backing", which is a thin, extra strong woven nylon cord and has provided good results. Not bad for my first time around, I'd say.

Now the radio picked up all local stations but after about 5 or 6 hours of continous operation, a loud crackle appeared all across the dial. No amount of tapping or moving of controls seemed to fix this.

Was it a broken solder joint or a short? Nope, everything seemed fine.

Turns out it was caused by the silver-mica capacitors in the IF transformers going bad. The capacitor in these things consist of essentially a mica disk that is partially spray silvered on both sides (to make up the "plates" of the capacitor). Contact "fingers" inside the base of the transformer contact the silvered surfaces.

The edges of the disk, however are not silvered, in order to not let the two "plates" touch each other and short out. With age, the silver somehow made its way to the edge, tarnished and was shorting out intermittently.

Replacement of this capacitor is the only solution. For that you have to disconnect all the leads going to the transformer and then un-mounting the device from the chassis.

In this case, the thing was held to the chassis by a bolt and nut. Removing the nut allowed me to lift the transformer out.

Make sure you pay attentino to the mounting marks of the device, since it only will go in one way. In this case, there was a little arrow marking direction.

Next you have to prize off the aluminium shield that encloses the innards.

Then you remove the coil from its mount and disconnect the leads. Do this carefully since the wires are thinner than human hair, it seems. Make note of which is the primary and which is the secondary and which is the top part of the coil.

Now was the fun part. Getting into the capacitor assembly. Luckily in this case, all I had to do was undo a second nut that held two phenolic wafers in place, forming a sandwich with the mica disk in place.

Removing the nut allowed the mica disk to slip out. Trim the tabs on the contact "fingers" so that they don't touch each other and re-do the "sandwich".

I then used teeny-tiny mica capacitors (100 picofarads at 300 volts) and mounted them to the same terminal points that were used for attaching the transformer coil wires. Keep the leads as short as possible.

Reattach the coil, paying attention to the proper connections, replace the shield and then place the assembly back on the chassis. Mind the original orientation of the device. Bolt firmly in place, but don't overtighten the nut, obviously.

Reconnect leads in the appropriate places and then it's time to test.

You will have to align the radio again. I did a quick and dirty alignment of the tuning condenser but didn't do the IF adjustments. It's still tracking quite well, although I will have to gather up the courage to apply an alignment tool to the transformer cores so I can finish this properly.

The radio now works properly.

FrankB · 12th Nov 2005, 12:12 am

The problem with silver migration is quite prevelant in the old sets.

If you havent checked into the archives at Antique Radio Forum , I suggest you might find more info on this problem.

There have been some rather lengthy discussions on this and the same solution as you performed.

Nice looking Zenith too.

If the clock motor stars getting noisy or gums up there are a couple of easy fixes for that.

howard · 13th Nov 2005, 2:43 pm

Hello Stephanie,

Gosh, you certainly know your way around old valve radios ! Thats a nice old clock radio and good to see it working again

Howard

PS: And an interesting, but maybe at times troubled, journal webpage too

Mike Phelan · 14th Nov 2005, 8:52 am

Quote:

Originally Posted by FrankB

If the clock motor stars getting noisy or gums up there are a couple of easy fixes for that.

One of these is never to go anywhere near it with WD40 or any other solvent!

Another is not to use any old oil or grease. Give me a shout is you want more info on this, Stephanie.
If you want to run a 110v clock motor, do as Goblin did in later clocks - put a 12k 2w resistor in series with it.

Station X · 14th Nov 2005, 11:17 am

Quote:

If you want to run a 110v clock motor, do as Goblin did in later clocks - put a 12k 2w resistor in series with it.

Won't the clock in this radio be designed to work on a 60 Hz supply?

Graham.

Mike Phelan · 14th Nov 2005, 11:39 am

Quote:

Originally Posted by G4ILN

Won't the clock in this radio be designed to work on a 60 Hz supply?

Graham.

Quite right, Graham. What I omitted to say (common first thing in the morning!) , and what Goblin did (and Zenith may do) is to swap one of the wheels from (IIRC) 35 to 42 teeth.

Some clocks like Ferranti had a rotor that had about 30 teeth and a C-shaped stator and just changed the rotor and stator to ine with more teeth.

Probably be easier that doing a power oscillator with q***tz movement.

OTOH, you could just leave it running slow! Don't tell my wife, though. She is sometimes not too enamoured with my clock menagerie not all keeping perfect time!

mikelect · 14th Nov 2005, 11:57 am

Quote:

Originally Posted by Mike Phelan

Quite right, Graham. What I omitted to say (common first thing in the morning!) , and what Goblin did (and Zenith may do) is to swap one of the wheels from (IIRC) 35 to 42 teeth.

Some clocks like Ferranti had a rotor that had about 30 teeth and a C-shaped stator and just changed the rotor and stator to ine with more teeth.

Probably be easier that doing a power oscillator with q***tz movement.

OTOH, you could just leave it running slow! Don't tell my wife, though. She is sometimes not too enamoured with my clock menagerie not all keeping perfect time!

This is all immaterial Stephanie is in New York anyway

and I'd guess they'd have a 110v 60 Hz supply to hand

Mike

Mike Phelan · 14th Nov 2005, 12:09 pm

Quote:

Originally Posted by mikelect

This is all immaterial Stephanie is in New York anyway

and I'd guess they'd have a 110v 60 Hz supply to hand

Mike

So she is! I suppose it was more of a generic question.
Think I'll go back to bed, Mike.

Saves dripping all over the keyboard

stephanie · 14th Nov 2005, 4:34 pm

Correct. I live in New York.

Our local voltage is about 118 volts, at 60 Hertz.

Thanks for the offer on the clock maintenace tips, though. I'm sure those things apply universally.

31st Oct 2005, 7:09 pm	#1
stephanie Retired Dormant Member Join Date: Jul 2005 Location: New Bern, North Carolina, USA Posts: 346	ZENITH C-519 clock radio (American set) Wow. Seems like I'm just cranking these ******* out recently. Note: Picture is "borrowed". http://radioatticarchives.com/images...-519_Shinn.jpg This one was a project I was fighting with for the better part of a year. This Zenith dates from around 1963 and uses a conventional American 5-tube series-string circuit (12AV6 detector, 12BA6 IF amp, 50C5 audio out, 35W4 rectifier, 12BE6 converter). It runs off 120 volts AC only, however because of the clock motor. If this motor were taken out of the equation, the radio would be perfectly happy on 120 volts DC. I picked it up for a tenner (American dollars) at a swap meet back in 2003 and sat around until earlier this year when I finally got to it. When obtained, the set was faintly picking up some stations. The volume control was frozen in place and the tuning mechanism also suffered from crusty grease. There were two wax paper capacitors to be replaced under the chassis plus the mains filter. A bit of contact cleaner and a drop of lightweight sewing-machine oil unstuck the volume pot and while messing around under the chassis, I also managed to break the already rotten tuning drive string. This was replaced with "fly fishing line backing", which is a thin, extra strong woven nylon cord and has provided good results. Not bad for my first time around, I'd say. Now the radio picked up all local stations but after about 5 or 6 hours of continous operation, a loud crackle appeared all across the dial. No amount of tapping or moving of controls seemed to fix this. Was it a broken solder joint or a short? Nope, everything seemed fine. Turns out it was caused by the silver-mica capacitors in the IF transformers going bad. The capacitor in these things consist of essentially a mica disk that is partially spray silvered on both sides (to make up the "plates" of the capacitor). Contact "fingers" inside the base of the transformer contact the silvered surfaces. The edges of the disk, however are not silvered, in order to not let the two "plates" touch each other and short out. With age, the silver somehow made its way to the edge, tarnished and was shorting out intermittently. Replacement of this capacitor is the only solution. For that you have to disconnect all the leads going to the transformer and then un-mounting the device from the chassis. In this case, the thing was held to the chassis by a bolt and nut. Removing the nut allowed me to lift the transformer out. Make sure you pay attentino to the mounting marks of the device, since it only will go in one way. In this case, there was a little arrow marking direction. Next you have to prize off the aluminium shield that encloses the innards. Then you remove the coil from its mount and disconnect the leads. Do this carefully since the wires are thinner than human hair, it seems. Make note of which is the primary and which is the secondary and which is the top part of the coil. Now was the fun part. Getting into the capacitor assembly. Luckily in this case, all I had to do was undo a second nut that held two phenolic wafers in place, forming a sandwich with the mica disk in place. Removing the nut allowed the mica disk to slip out. Trim the tabs on the contact "fingers" so that they don't touch each other and re-do the "sandwich". I then used teeny-tiny mica capacitors (100 picofarads at 300 volts) and mounted them to the same terminal points that were used for attaching the transformer coil wires. Keep the leads as short as possible. Reattach the coil, paying attention to the proper connections, replace the shield and then place the assembly back on the chassis. Mind the original orientation of the device. Bolt firmly in place, but don't overtighten the nut, obviously. Reconnect leads in the appropriate places and then it's time to test. You will have to align the radio again. I did a quick and dirty alignment of the tuning condenser but didn't do the IF adjustments. It's still tracking quite well, although I will have to gather up the courage to apply an alignment tool to the transformer cores so I can finish this properly. The radio now works properly. Last edited by mikelect; 31st Oct 2005 at 8:20 pm. Reason: vernacular

12th Nov 2005, 12:12 am	#2
FrankB Heptode Join Date: Oct 2005 Location: Olympia, Washington, USA. Posts: 664	Re: ZENITH C-519 clock radio (American set) The problem with silver migration is quite prevelant in the old sets. If you havent checked into the archives at Antique Radio Forum , I suggest you might find more info on this problem. There have been some rather lengthy discussions on this and the same solution as you performed. Nice looking Zenith too. If the clock motor stars getting noisy or gums up there are a couple of easy fixes for that.

13th Nov 2005, 2:43 pm	#3
howard Nonode Join Date: May 2005 Location: Godalming, Surrey, UK. Posts: 2,593	Re: ZENITH C-519 clock radio (American set) Hello Stephanie, Gosh, you certainly know your way around old valve radios ! Thats a nice old clock radio and good to see it working again Howard PS: And an interesting, but maybe at times troubled, journal webpage too Last edited by howard; 13th Nov 2005 at 2:58 pm.

14th Nov 2005, 4:34 pm	#9
stephanie Retired Dormant Member Join Date: Jul 2005 Location: New Bern, North Carolina, USA Posts: 346	Re: ZENITH C-519 clock radio (American set) Correct. I live in New York. Our local voltage is about 118 volts, at 60 Hertz. Thanks for the offer on the clock maintenace tips, though. I'm sure those things apply universally.