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 Post subject: Ballast Tube Question
PostPosted: Feb Sat 09, 2019 8:02 pm 
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Joined: May Thu 12, 2016 4:36 am
Posts: 61
Location: Niagara Falls, Canada
Hi:
Recently picked up a Air King Model 257 all tubes checked out okay except ballast tube originally came with a M49HG however it was substituted out with a universal 23-55-F that has no reading across pins 2-3 was wondering if anybody had any experience taking one of these apart before I make a attempt at it. I'm thinking I might be able to repair it.
Thanks
Sidevalvebob


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 Post subject: Re: Ballast Tube Question
PostPosted: Feb Sat 09, 2019 11:47 pm 
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Joined: Feb Mon 21, 2011 4:19 pm
Posts: 177
Location: San Marcos, CA 92069
Your tube line up is 68V at 0.3amps. The ballast tube is dropping 52V for a 120V line voltage. You could replace the ballast tube with an 8uf 250vac rated capacitor. An 8uf capacitor will drop about 60VAC at 0.3ma, providing 60VAC for the tube heaters. That is slightly lower than the 68V they are rated for, but it won't harm them. Using an AC capacitor will eliminate the heat of the ballast tube.

If you do this, disconnect pin 3 so the ballast tube is no longer in the circuit. Otherwise if some plugs in a good ballast in the future, one or more tubes will burn out in a short time.

Use something like this https://www.amazon.com/PODOY-CBB61-Ceiling-Capacitor-250VAC/dp/B0143VJN40


Last edited by nash on Feb Sun 10, 2019 12:19 am, edited 2 times in total.

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 Post subject: Re: Ballast Tube Question
PostPosted: Feb Sun 10, 2019 12:16 am 
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Joined: Feb Sat 06, 2016 1:47 am
Posts: 2769
Location: La Mesa Califonia
You can keep the radio wired as is. Use the shell of the ballast tube and base. Here's a how to from my pal Jeff at the Antique Radio Store. About half way down the page. For dial light use #44 bulb with 47 Ohm resistor across the bulb in series with the heater string.

http://www.oldradiosrus.com/build.html

Capacitor to use.

https://www.digikey.com/product-detail/ ... ND/4694508


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 Post subject: Re: Ballast Tube Question
PostPosted: Feb Sun 10, 2019 9:24 pm 
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Joined: May Thu 12, 2016 4:36 am
Posts: 61
Location: Niagara Falls, Canada
Thank you nash and thunderbird281 for your advice and recommendations late last night was able to remove top cover off the ballast tube. Interesting how they made these, the mica board acts as a insulator as well as a thermal conductor. I included two pictures, first picture shows resistance wire comming off pin 2 it's separated at the board terminal and broken near the top of the insulating board. Picture two shows the resistance wire coming from pin 3 and where the wire has separated. Not sure if this can be repaired if not will follow your recommendations. will get the resistors and capacitor on the next order I put in.


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 Post subject: Re: Ballast Tube Question
PostPosted: Feb Sun 10, 2019 11:00 pm 
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Location: La Mesa Califonia
Not fixabe. Can't solder wire. Also all the wire is fatigued .


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 Post subject: Re: Ballast Tube Question
PostPosted: Feb Tue 12, 2019 12:50 am 
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Location: In the village, 19115
thunderbird281 wrote:
Not fixabe. Can't solder wire. Also all the wire is fatigued .


Also the wire gets hot, solder will melt. :shock:

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I like things that light up, tubes, bulbs, LEDs, whatever, and things that make noise.


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 Post subject: Re: Ballast Tube Question
PostPosted: Feb Tue 12, 2019 3:56 am 
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Joined: Sep Tue 30, 2014 6:08 am
Posts: 3776
Location: The Old Dominion VA 23518
FYI, American Radio History has the two Ballast Tube manuals:

Reference:

https://www.americanradiohistory.com/Ar ... ok-opt.pdf

and substitution:

https://www.americanradiohistory.com/Ar ... de-opt.pdf

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"Capacitor Cosmetologist since 1979"
USN Retired 1984-2006 (Avionics/Cal)


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 Post subject: Re: Ballast Tube Question
PostPosted: Feb Tue 12, 2019 2:30 pm 
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Joined: May Thu 12, 2016 4:36 am
Posts: 61
Location: Niagara Falls, Canada
Thank you thunderbird281, Number 6, Findm-Keepm for all your help, these ballast tubes remind me of a mini toaster lol. I've added the ballast tube files to my collection and now have a list of substitute tubes. Got my fingers crossed there is a hamfest in Burlington Ontario Canada this weekend hopefully I will come across another tube or the resistors and capacitor I need for the conversion. Even if I find another tube I will do the conversion on my old tube regardless.

Thanks Again
Sidevalvebob


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 Post subject: Re: Ballast Tube Question
PostPosted: Feb Tue 12, 2019 3:46 pm 
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Joined: Jul Mon 26, 2010 8:30 pm
Posts: 24991
Location: Annapolis, MD
nash wrote:
Your tube line up is 68V at 0.3amps. The ballast tube is dropping 52V for a 120V line voltage. You could replace the ballast tube with an 8uf 250vac rated capacitor. An 8uf capacitor will drop about 60VAC at 0.3ma, providing 60VAC for the tube heaters. l]

A nitpick here, if I may. The capacitor voltage is out of phase with the resistive load of the filaments, so the two add as vectors:

Vc = cap voltage
Vr = voltage

Supply = 120 = square root ( Vc^2 + Vr^2)

OR
Vc = square root (120^2 - Vr^2)

<<same formula to get Vr, when you know Vc---just swap the two>>

The drop on the capacitor:
Xc = 0.159 / (f*C) = 0.159 / 480E-6 = 331 ohms

at 0.3mA, that gives us ~ 100 volts on the cap, so the load voltage will be square root( 120^2 - 100^2 ) = ~66 volts

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"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Ballast Tube Question
PostPosted: Feb Wed 13, 2019 9:39 pm 
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Joined: May Thu 12, 2016 4:36 am
Posts: 61
Location: Niagara Falls, Canada
Thank You pixellany for your input the information is very much appreciated.

Sidevalvebob


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