[Boatanchors] [Hammarlund] Comet Pro Trasformer Went South(Part 2)

[Richard Knoppow]

----- Original Message ----- 
From: "Joe Connor" <joeconnor53 at yahoo.com>
To: "Joe Connor" <joeconnor53 at yahoo.com>; 
<boatanchors at mailman.qth.net>; <hammarlund at mailman.qth.net>
Sent: Sunday, July 14, 2013 9:34 PM
Subject: Re: [Hammarlund] [Boatanchors] Comet Pro Trasformer 
Went South(Part 2)


Thanks for all the advice. I've run all the tests that you 
suggested and it appears that the power transformer is 
shorted.

I just want to rule out a problem with the 2.5V filament 
chain. The 2.5V filament secondary is center-tapped. The 
center-tap goes through a 450-ohm resistor to ground 
(bypassed by an 8 mfd cap).With the center tap disconnected, 
the resistance from the center tap to each 2.5V filament pin 
is less than 1 ohm. The resistance from the disconnected 
center tap to ground is 1.5 ohms. Thus, when the center-tap 
is connected, it is as if the 450-ohm resistor isn't even 
there. With the center tap disconnected, each filament pin 
reads 1.5 ohms to ground. Is that another problem?

To avoid confusion, the schematic can be found here 
http://www.nostalgiaair.org/PagesByModel/994/M0008994.pdf at 
Hammarlund 3-2.

Thanks.


     You can eliminate the receiver circuits by 
disconnecting the transformer and running the receiver from 
an external supply.  That way you can tell if something in 
the receiver is shorted or if the transformer had a fault. 
Its possible there was moisture in the transformer which 
caused it to arc and short.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com