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Antique Radio Technical Forum
Majestic Model 70B

Posted by Terry on 11/17/2005 20:44

:Hello all. Let me know if I missed something, but so far, since I read through all of this thread, I have seen no mention of removing and testing filter condensers. Again, perhaps I missed something. Why not remove all of the condenser leads from the power supply and then test resistances. Check condensers individually for shorts and leakage (acceptable condensers have NO leakage, NOT EVEN IN THE MILLIONS OF OHMS).
:

Thomas,

I removed all the wires and checked the condensors. I have readings, but how do iIknow what they should be?

I also checked the resistors and found the 4180 ohm to be 7.26K ohm. I replaced it with a series set up and now have 4.3K ohms. The other two were right 1.048K and 17.4K ohms

Terry
:With all condensers removed, you should be able to check all of the resistors without removing them, save those which connect from the resistor bank to B-. As I said before, it is very rare that resistors decrease in value. These decreases in value lead me to believe that condensers are shorted and are causing these low values. Resistance checks, when dealing with old condensers, which more likely than not are leaky, cannot be accurately made until all condensers are removed. It is very bad practice to turn on an old radio and make voltage checks without first checking the components. It is extremely bad practice to assume that all of the condensers in such an old radio are still good. All of the condensers and resistors should be checked individually, one at a time, by removing them from the circuit. Only after all bad components have been replaced should the radio be fired up. Until then you are only asking for trouble if you try to find the problem by using voltage checks. You may damage the power supply further. The only voltage checks that should ever be made on a radio prior to examining components as stated exactly above, are AC voltage checks. These are made with all tubes removed. Voltage is tested at the rectifier plate pins, filament pins, and at all other tube filament pins. Only after all components have been tested and bad ones replaced, should DC voltage checks be made after carefully powering up the radio for the first time with all tubes in place. As I said before, firing up a radio in unknown electrical condition puts terrible stress on parts when some are malfunctioning and you don't know which ones are malfunctioning.
:
:Also, unless the wiring is all rubber and is falling apart, you don't usually need to replace all of it. From my experience, some Majestics use rubber wiring even at this early time (rubber wire is often dried up and terrible to work with), but otherwise cloth wire is often encountered. Cloth wire doesn't usually fall apart unless the radio has been baked in an attic, soaked in water, or invaded by mice.
:
:Thomas



Majestic Model 70B 
Terry 11/03/2005 20:06 
Norm Leal 11/04/2005 08:51 
Radiodoc 11/04/2005 09:12 
Radiodoc 11/04/2005 13:07 
Terry 11/05/2005 15:25 
Radiodoc 11/05/2005 20:40 
Terry 11/06/2005 20:54 
Radiodoc 11/07/2005 10:42 
Terry 11/07/2005 19:48 
Radiodoc 11/07/2005 21:43 
Terry 11/08/2005 20:57 
Radiodoc 11/09/2005 10:23 
Terry 11/09/2005 20:07 
Terry 11/09/2005 21:16 
Radiodoc 11/10/2005 08:58 
Terry 11/10/2005 21:11 
Radiodoc 11/11/2005 14:11 
Terry 11/11/2005 20:50 
Radiodoc 11/11/2005 22:22 
Thomas Dermody 11/12/2005 01:52 
Terry 11/12/2005 19:34 
Radiodoc 11/14/2005 10:07 
Terry 11/14/2005 19:31 
Radiodoc 11/14/2005 22:26 
Terry 11/15/2005 19:23 
Radiodoc 11/15/2005 20:22 
Terry 11/16/2005 08:02 
Radiodoc 11/16/2005 08:43 
Terry 11/16/2005 13:13 
Radiodoc 11/16/2005 15:09 
Terry 11/16/2005 20:40 
Radiodoc 11/17/2005 09:05 
Thomas Dermody 11/17/2005 17:09 
Terry 11/17/2005 20:44 
Thomas Dermody 11/18/2005 00:32 
Thomas Dermody 11/18/2005 02:43 
Thomas Dermody 11/18/2005 12:19 
Terry 11/30/2005 20:09 
Thomas Dermody 11/30/2005 23:38 

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