Zenith Radio 50A1 Ballast Tube Solid State Replacement.

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Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Rudy Transfeld on Sun Mar 11, 2018 1:22 am

I've had two Zenith radios sitting for nearly 2 years with each a blown 50A1. Done a lot of research and found a solid state replacement available or build one yourself which I did this weekend with great results. If anyone is interested in a stage by stage description with photos as well as a copy of how it was done, I would be only too happy to share it with you.
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Rudy

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by jukeboxman on Sun Mar 11, 2018 7:47 pm

WELCOME to TRF--very nice thank you

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Rudy Transfeld on Mon Mar 12, 2018 6:15 am

Hi Gary,
Not sure if you want me to send them or just congratulating me for offering. There are 7 photos which are used in my description, just read all about uploading photos, is that  too many.
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Rudy

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Chas on Thu Mar 15, 2018 12:06 am

I don't think that is too many photos to tell the story...

Schematic, parts list and how you coped with a button base to plug into the 9-pin wafer socket would be interesting... Many have gotten creative cutting up a glass 9-pin tube for a base...

I suppose that covering the socket and hard wiring the regulator would work too.

I have "converted" two of my T.O's less the 50A1. I used a resistor value that also compensated for the silicon diode replaced selenium rectifier at 125 volts input. I made a removable cover for the 9-pin socket. There is at least one model T,O. that does not use the 50A1 in my collection. That was my inspiration to simply leave it out...

YMMV

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Rudy Transfeld on Fri Mar 16, 2018 2:26 am

Hi Chas,
First of all I was lucky enough to have a 9 pin male socket, I found them in my socket box.
The schematic was downloaded from " Antique Radio Forums" a couple of years ago, it is no longer visible there. The T/O you could be referring to is a model H500. I have one of them as well as 2 x A600, one is 115 volt and the other has a 240-115 volt module.
I bought 5 x IXCP10M45S from e-bay a year or so ago and it wasn't until now that I had the courage to tackle both 600s. One had a blown 50A1 with unknown problems  and the other  distorted sound.
The recommended value of resistors are 33 ohm and 600 ohm, I used 2 x 1.2k in parallel.I tried to make the bundle as snug as possible by using a long heat sink.
When I completed one I tentatively wound up the variac, until it reached full mains voltage, no smoke no bangs which was a relief. B+ was 105v and filaments was 9.1v. Then spent many hours fixing the original problems.To cut a long story short, the distortion was caused by an O/C C41D, and other had issues with a faulty 1L6-1U5-1U4 & 3V4 apart from high valued resistors
Just for the exercise, I cut the base of a tube using a Dremel  with diamond disc, nearly all came off neatly except for the last bit.There is no way in the world that the pins can be soldered, I cleaned them until they were shining, used liquid flux and it did not even tin up. I then used the glass and squeezed a spare board into the glass, super glued it and it was done. I should have cleaned the glass interior and marked the 50A1 on the heat sink. Not sure if you know the trick of using super glue, have some sodium bicarbonate of soda( baking powder) ready and sprinkle the wet super glue with it, it will harden instantly.
I now have two working Zenith T/O.
Regards
Rudy
PS My son suggested the link for the photos.

https://imgur.com/a/qH5AZ

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Chas on Fri Mar 16, 2018 12:55 pm

Rudy,

I took the time to upload your images of the 50A1 Solid-State.

Well done!

Thanks!

Chas













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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Chas on Fri Mar 16, 2018 1:05 pm

Rudy,

I use a plumbers liquid flux, on steel, nichrome and some stainless steels. Used very sparingly, it evaporates under heat and allows for use of common solder for connections.
Works well on most stranded wire that has become oxidized from rubber insulation, sweating chassis rivet connections that are oxidized and other stubborn connections.
Be aware that it is hard on iron plated soldering iron tips and accelerates dissolution of copper tips.

YMMV

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by terrydec on Sat Mar 17, 2018 1:50 am

Super Cool!

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Bill Cahill on Sat Mar 17, 2018 10:15 am

Thanks for showing the wonderful work done. Would you be willing to fabricate two for me? I need one for an RCA, and, the other for an H500 Zenith. Both of my 50A1's are blown. In fact, one is missing.
Bill

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Rudy Transfeld on Sun Mar 18, 2018 1:01 am

Hi Bill, I don't mind doing it, the only problem is that I have one 9 pin male socket left which I was going to use making a 1L6 solid state tube.
There is a company in California that sell vintage parts, I noticed the same 9 pin male socket in their picture, if you can buy a few of them I'd be happy to make them at cost price +postage.
http://www.ultraelectronicactive.com/elx/Vintage-Cables+Connectors.html

Rudy

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Rudy Transfeld on Sun Mar 18, 2018 2:02 am

Hi Bill,
I just bought 4 x sockets from e-bay, they are a socket adapter but I'm pretty sure I can work with it. Item number is 122921329727.
I spent quite a bit of time searching for the type I have and gave up, hence the above.
I'll make them and get a price to post them to the US, then let you know the total cost, it will be heaps cheaper than the one on e-bay.
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Rudy

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Chas on Sun Mar 18, 2018 11:47 am

Rudy,

Heads up, you will need a 7-pin B7G male plug for developing a replacement for a 1L6.

The bases commonly referred to as "miniature" are the 7-pin B7G type, (or "small-button" or "heptal") and the slightly later 9-pin B9A (Noval).

YMMV

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Rudy Transfeld on Sun Mar 18, 2018 6:56 pm

You're right of course, how dumb of me, must be the heat getting to me.
Having trouble sourcing the recommended JFETs & Cmos ECG312-ECG222, at a reasonable price.
Rudy

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Chas on Sun Mar 18, 2018 9:42 pm

Rudy, Et Al,

I save antique radio data bits to the hard drive. I have a system of directories, it ain't perfect but I found this in a couple of minutes.

Hope it helps all:

Text extract from ARF member letter to Amperite, its not dated so I don't know if it is stale, file says, Mon 02 Nov 2009: The ARF article: Mar 14 2007 at http://antiqueradios.com/forums/viewtopic.php?t=68641&start=20

Moose wrote:Hello Moose,

Following are the specifications for the two ballast regulator tubes you are inquiring about:

D5TF30:
glass envelope size - T- 6 1/2
heater coil voltage range: 30 to 60 Volts
regulating current: .048 to .055 Amperes

50A1
glass envelope size - T- 6 1/2
heater coil voltage range: 30 to 65 Volts
regulating current: .05 to .058 Amperes

Pin connections should be identical.
In my opinion, ballast regulators are interchangeable-

Let me know if you need any additional information.

Frank M. Kretkowski
Technical Support
Amperite Co.
North Bergen, NJ
800-752-2329

And for the 1L6: An old jpg, again, the archive date is Sun 17 Apr 2011:



Um, I suspect that the RF/OSC alignment would have to be touched up on all bands...

Re-using a glass envelope is tricky, for the 50A1 poor heat dissipation. There are such products as phenolic tube and thin wall aluminum tube lined with fish paper then covered with thin heat shrink, extend the aluminum to increase the dissipation the shrink removes and conceal the bent over tab that mounts the regulator...

Is that aluminium Smile

The should be Australian sources like Mc-Master Carr in U.S. Suppling everything to anybody...

You may have to make changes in choices for active components for the 1L6, Consider an all SMD construction and a PC board.

If your bench is equipped to service SMD with an old toaster oven your in the production biz.

Find-A-Tube.com is currently pricing the 50A1 at...$29 new, $15 used... 1L6 $29 new, $18 used.

Good Luck!

BTW it's 30 deg F, still some 4" of gravelly snow on the ground. It should all go in the next 10 days with the coming rain...

Chas


Last edited by Chas on Sun Mar 18, 2018 9:45 pm; edited 1 time in total (Reason for editing : Added paragraph...)
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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Rudy Transfeld on Mon Mar 19, 2018 3:03 am

Hi Chas,
Thanks for the info. perhaps Bill should consider a used 50A1, the cost postage from here to the US is the expensive part.
I have worked on SMD, can't say a like it much, in fact only last week I tackled our faulty Panasonic Plasma with lots of shorting SMD components on the SN board, all I've got to do is source them from all over as Panasonic along with Sony are not very helpful if you're not a service agent. I'll put the 1L6 project on hold as I have quite a few jobs on the go at the moment and am prioritizing doing the important ones first.
My solid state 50A1 is running surprisingly cool, after about an hour I was able the touch the heat sink without getting burnt, it's not in a glass envelope, I only did one to see if it could be done.
Just checked your weather and it's  a bit too cold for us. Temperature in Brisbane today is 31c /88 f quite a warm day for autumn / fall, particularly when the humidity was quite high as well. Living in the sub-tropic has its advantages but the older we get the more we don't like the heat. Our house is fully air conditioned which makes it easier to live with.
There's a show on TV called House Hunters which we watch nightly and it give us a good idea of what it's like to live in the US. Your houses are very cheap, price wise, compared to ours, some are beautiful mansion which would sell for 4 times the price over here.
Anyway, I've had a long day today, so I'll sign off.
Regards
Rudy

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Bill Cahill on Mon Mar 19, 2018 11:05 am

I'll also hold off. Looks like buying used ones is the best thing to do. Thanks, guys.
Bill Cahill

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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by easyrider8 on Tue May 08, 2018 2:12 am

If you are not going to a country where they have large fluctuations in voltage, replacing the 50A1 with a 1300 ohm 10 watt resistor works fine.

Dave
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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

Post by Chas on Tue May 08, 2018 9:54 am

Zenith built a T.O. without the ballast. FWIK there was never a tube burnout issue in it.

None the less, there are bias networks of resistors around the filaments, in any T.O. These low ohm resistors tend to drift. Checking and replacing these resistors will help in correcting bias and tube filament voltage.

YMMV
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Re: Zenith Radio 50A1 Ballast Tube Solid State Replacement.

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