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Unknown Radio with JFD Ballast

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Forum » Valves / tubes - Semiconductors » Other valves/tubes » Unknown Radio with JFD Ballast
           
Kerry McCowen
 
 
USA  Articles: 3
Schem.:
Pict.: 3
19.Jul.20 19:46
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I have, what I would call an American 4 + a ballast tube (no transformer) that I cannot identify. Never the less without a schematic I have replaced the capacitors - nothing else. After cap replacement, radio tuned in one broadcast station weakly, which I assumed was due to a poor loop antenna. Soon though the 25z5 tube burned out. At this point I'm assuming JFD the ballast tube is bad. The ballast has only 3 pins in use, 3,7 and 8. It does test 25 ohms on 8, 60 ohms on 7 and 188 ohms on 3.  Tubes are 25z5 Rectifier, 6K7 Amplifier, 6F5 high mu Triode, 25L6 Beam Pentode Power output. I need help to answer the following:

1. The Ballast Tube needs to be ID'd so I can order another. I have a copy of the JFD manual 1947, but I find no matching Ballast with 5 pins cut. 

3. It would be nice to know what radio it is and to have a schmatic if someone has one, by using Radio Nostalgia, the only radio that comes up using the above tubes in a Trav-ler 420A, but the schematic doesn't fit what I have. 

4. If someone can answer why only 3 pins are in use but 5 pins are connected to various components, 255z5 tube, volume potentiometer, power switch, #46 bulb. I can be more specific if needed.  

Any help would be appreciated. Pictures attached. More can be uploaded if needed. 

N0KAM - Kerry



 

Attachments:

Gidi Verheijen
Gidi Verheijen
Officer
NL  Articles: 204
Schem.: 1880
Pict.: 2360
20.Jul.20 03:09
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Hello Kerry,

There are several USA models with the tube set 6K7, 6F5, 25L6 and 25Z5. However, most models are not equipped with a ballast tube, but with a resistor in the line cord (e.g. Autocrat 104, Warwick 401 and 402, Gamble 401). Some Spiegel and Detrola models have the same tube set.

There are at least two models with the tube set 6K7G, 6F5G, 25L6G and 25Z5 plus ballast tube L55B: Trav-Ler 420A (already identified by you) and Trav-Ler 420S.

Ballast tube L55B has connections to pins 3, 7 and 8. Pin 3 and 7 are connected to the outer ends of a resistor and pin 8 to a tap. The other pins are not connected, so they may be used as soldering supports.

      

            Ballast tube L55B

 

Gidi Verheijen

 

 

Daniel Consales
Daniel Consales
 
D  Articles: 175
Schem.: 289
Pict.: 184
20.Jul.20 11:04
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Hello Mr. McCowen,

you didn't mention your mains voltage. Considering the tubes and the resistor value of the ballast this set is designed for 115/117 volts mains.

D. Consales

Kerry McCowen
 
 
USA  Articles: 3
Schem.:
Pict.: 3
20.Jul.20 15:16
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Gidi 

Thanks for the reply. After reading you post I performed another search this time including radios listed with five tubes instead of just 4 - many entries show the ballast as a tube. This gave me many more hits and the L55B came up often. While I still did not find an exact match, there are many schematics that will help. The use of some blank socket pins for soldering posts is correct, I apologize for missing that. I now have many more schematics printed out to pour over.

Kerry

 

 

 

 

Kerry McCowen
 
 
USA  Articles: 3
Schem.:
Pict.: 3
20.Jul.20 15:20
Reply  |  You aren't logged in. (Guest)   5

Daniel,

Yes you are correct, it is designed for 115/117 mains. Plus I have identified the correct plug position so the chassis does not become "hot". Thank you for your reply.

Kerry

  
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