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crosley: Ch= 7H3 (7 H 3); 72LB Lowboy

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » crosley: Ch= 7H3 (7 H 3); 72LB Lowboy
           
Dave Turner
 
 
USA  Articles: 52
Schem.: 8
Pict.: 17
02.Apr.09 19:05
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I've been "studying" this old chassis for a while.
I put it on my dim bulb tester with a 60w bulb and the bulb does not dim, and none of the tubes light up.  However, two tubes, (69 and 70 on the schematic) a 6D6 and a 6B7, have broken cap connections.  I've ordered two new tubes to replace but don't have them yet.
Meanwhile, since this is a 75W or 100W power requirement, I exchanged the bulb for a 250W, (didn't have a 75 or 100), turned it on and the 250 bulb is very dim and the chassis started to smell and I could hear it "cooking". Transformer was getting warm.
 
Did I burn it up?
 
I'd really like to get this old radio running, but fear a new transformer will be pretty costly, and have no idea where to search for one.  The whole radio is probably worth a hundred bucks.
 
Hope you can give me some ideas.
Dave
Mario Bermejo
Mario Bermejo
 
RA  Articles: 237
Schem.: 211
Pict.: 78
02.Apr.09 20:45
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Hi Dave, if you use a series light bulb the voltage applied to the transformer will be substantially lower and therefore you cannot expect the tubes to light up. If the transformer is bad, it probably was that way before you started your tests. You need to make sure there are no shorts on the transformer secondary (80 tube, electrolitics, etc) before applying any power. The smell can come from a number of different parts, did you visually inspect the chassis?

Since you did not get full bright in your dimm bulb we can safely assume the transformer's primary is not shorted. The very dimm glow on the 250W bulb, on the other hand, indicates the primary winding is not open.

To properly finish testing the transformer, remove the 80 tube and connect to the mains. If you want to be 100% sure then disconnect all secondary windings as well. You should measure high tension, 5V for the 80's filament and 6,3v at the other filament winding.

Good luck.

This article was edited 02.Apr.09 20:52 by Mario Bermejo .

Dave Turner
 
 
USA  Articles: 52
Schem.: 8
Pict.: 17
02.Apr.09 22:20
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Thanks Mario,   If you bear with me, I'll ask some more questions. You stated:

>> did you visually inspect the chassis? 

Yes, I looked it over carefully, and I did find one wire leading to tube 80 that looked as if the insulation was burned off, but not burned through, in a section about 1/2" long or less.

>>Since you did not get full bright in your dimm bulb we can safely assume the transformer's primary is not shorted. The very dimm glow on the 250W bulb, on the other hand, indicates the primary winding is not open. 

ie: shorted out?

 >>To properly finish testing the transformer, remove the 80 tube and connect to the mains.  

Not sure what "connect to the mains" means

Sorry for my ignorance, but I'm trying.

Thanks, Dave

 
 

Mario Bermejo
Mario Bermejo
 
RA  Articles: 237
Schem.: 211
Pict.: 78
02.Apr.09 23:15

Count of Thanks: 1
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No problem at all Dave, can you post a picture of the underside of the chassis showing the transformer connections? This way we can figure it out together.

Mario

 

Dave Turner
 
 
USA  Articles: 52
Schem.: 8
Pict.: 17
18.Apr.09 15:32
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Getting back to this old 7H3, I did confirm that the transformer is 'gone'!  Also, the speaker coil has mega resistance.  I understand this is a vital part of the circuitry on this chassis.  sounds like I have major problems.  I'm about ready to put this one on the shelf or pass it one to someone who is capable of repairing it.  I really hate to do that, it's a nice looking dial with the 82:1 ratio 'fishing rod' tuning dial.

Anyway, I'm going to try to post the requested pictures here, in hopes that the generous wisdom of this list has some beneficial guidance for me.

 

 

Attachments:

Dave Turner
 
 
USA  Articles: 52
Schem.: 8
Pict.: 17
18.Apr.09 16:48

Count of Thanks: 1
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Will attempt to load some better pictures regarding my last message, on The poor old Crosley.

Dave

Attachments:

  
rmXorg