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 Post subject: Ballast tube/pilot light issue in Majestic model 50
PostPosted: Feb Fri 09, 2018 3:30 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1886
Location: Mesa, AZ, USA
I am working on a majestic model 50. Riders 8-1

The tube lineup is 25Z5, 43, 6D6, 6C6 and a ballast tube
The schematic does not give a number for the ballast, it just lists it as part number 16032.
A K49B ballast tube is in the set.
I got the radio working, although not well. The pilot light does not light.
Looking at the underside of the ballast tube socket, there is a 2K resistor between pins 7 and 8. These are the pins the pilot light wiring attaches to.

I measure several megaohms betwen pins 7 and 8 on the ballast tube. I opened it to see if the resistance wire was broken between the two pins, but it looks ok.

The 2K resistor is not in the schematics, although it looks factory original and untampered with. Somebody stick it in to pick up the slack for a gimpy ballast tube?


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 Post subject: Re: Ballast tube/pilot light issue in Majestic model 50
PostPosted: Feb Fri 09, 2018 4:03 pm 
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Joined: Nov Tue 08, 2016 5:59 pm
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Without a schematic I'm just spit-balling here, but I recently read an article written by Sylvania (from 1943) that suggested servicemen place a resistor in line with the pilot light to act as a drain should the bulb burn out. The intent was to protect the tube from full voltage should the bulb fail as a short.

Just a little food for thought.

Cheers,
Cliff


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 Post subject: Re: Ballast tube/pilot light issue in Majestic model 50
PostPosted: Feb Fri 09, 2018 5:36 pm 
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ASUMike wrote:
The schematic does not give a number for the ballast, it just lists it as part number 16032.
A K49B ballast tube is in the set.
Hi Mike,

The K49B is NOT the correct ballast.
The Ballast Tube Handbook shows the proper one as a K60C.

The K60 drops 60 volts versus 49 volts for the K49 (both at 300ma).
With today's higher line voltage, an even higher voltage (number > 60) might be desirable.

Additionally, your 49B has the wrong base (the B suffix should be a C). The suffix defines the ballast connections. The B suffix supports one panel lamp; the C suffix supports two.

ASUMike wrote:
I measure several megaohms betwen pins 7 and 8 on the ballast tube. I opened it to see if the resistance wire was broken between the two pins, but it looks ok.

The pilot lamp section of the ballast resistance is open. That could be due to a break in the actual element, or it could be a bad solder joint. In any case, it really is open.

The K prefix (K60C) means it expects 6.3v 150ma pilot lamps. Your C ballast expects two in series, so a drop of 12.6v. The 84 ohm (hot) ballast resistance would drop 12.6v @ 150ma since the total current through the ballast is 300ma.

The Rider page shows a #44 pilot lamp (6.3v 250ma), which does not match the ballast tube.

You might successfully sub an 1891 bulb (14v 230ma) with the C ballast.

Measure the voltage (AC) between pins 7 and 8. That will give us a starting point.
I'm guessing your tubes are running with reduced filament voltage.

- Leigh

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 Post subject: Re: Ballast tube/pilot light issue in Majestic model 50
PostPosted: Feb Fri 09, 2018 10:07 pm 
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First your schematic. http://www.nostalgiaair.org/pagesbymodel/508/M0010508.pdf

Next click this link will show you a couple different methods to solve your ballast issue with a lot less heat problems.
http://www.vintage-radio.com/repair-restore-information/valve_dropper-calcs.html

You can read all about it or just run down to the bottom of the page and download the zipped up file and get a nice
spreadsheet where you insert your information for your radio and it tells you what parts to use. So download
Droper Calculations Spreadsheet (ZIP file - file size 6k) and install it into your computer. In this case put in the following information. Supply voltage 125 volts and 60 cycles next your filament string.. include the bulb. 25 + 25 + 6.3 + 6.3 + 6.3bulb = 69 volts and insert 0.3 amps same as 300 mA. Insert 0 for surge limit drop and the calculator says that a 7.63 Mfd capacitor will replace your ballast. You will need a resistor in parallel with your #44 bulb as it draws 250 mA so you need a resistor to handle the other 50 mA. And presto no more ballast tube no more super heater from the ballast tube and your getting the correct voltage to the tube filaments.

the spread sheet also shows you the diode plus resistor method as well. But that method will also need an additional Zener diode in parallel with the dial lamp bulb to keep it from blowing at turn on of the radio.

As to the radio it is only a 4 tube radio including rectifier tube so don't expect too much from the actual 3 tube radio.

John k9uwa

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 Post subject: Re: Ballast tube/pilot light issue in Majestic model 50
PostPosted: Feb Sat 10, 2018 5:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1886
Location: Mesa, AZ, USA
First of all, thank you for all the really quality replies and advice. Before I discovered this forum I can honestly say I would not have understood any of the replies, but now I do, so the forum helps :-)

I managed to fix the K49B ballast tube. Got 28ish ohms between pins 7 and 8 now. Popped it in and the pilot light works. The radio works much better than before too.
For those that are curious, I measure about 3V between pins 7 and 8 for the pilot lamp, and 55V across the other section.

I think the K49B must be the intended ballast for this set. The rider's schematic mentions that pins 3 to 7 of the ballast should be about 50 volts, and that the set takes a #44 pilot light. The schematic also shows a single lamp.

Leigh is undoubtedly right that a ballast that drops about 10 or more additional volts would be a better choice.
However since the radio is crap, and I am unlikely to ever use it once it is repaired, it gets to stay the way it is :-)

I did try the capacitor calculation thing for a set with a resistor line cord once. I had put a power resistor in the set to replace the line cord but that thing got hotter than hell. The chassis was really cramped and it seemed not a good idea. As I recall the capacitor needs to be bipolar and rated at some reasonable voltage. I had trouble finding a suitable part and gave up.


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 Post subject: Re: Ballast tube/pilot light issue in Majestic model 50
PostPosted: Feb Sat 10, 2018 5:19 pm 
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Joined: Jul Mon 26, 2010 8:30 pm
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Location: Annapolis, MD
k9uwa wrote:

As to the radio it is only a 4 tube radio including rectifier tube so don't expect too much from the actual 3 tube radio.

John k9uwa

Indeed!!
I think this tube lineup is the original econobox AC-DC design. Performance is "highly adequate" on strong local stations, which is all many people needed.

has someone already mentioned using a capacitor to drop some or all of the filament voltage?

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


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 Post subject: Re: Ballast tube/pilot light issue in Majestic model 50
PostPosted: Feb Sat 10, 2018 5:45 pm 
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Joined: Feb Sat 06, 2016 1:47 am
Posts: 2145
Location: Santee Calif. 92071
You can use this AC capacitor in series with the filament string. The #44 dial light is also in series with filament string and use a 47 ohm 1 watt resistor across the dial light. This all makes a slow warm up start with no heat runs cool.

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


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