[GreenKeys] Hi Temps. in the Bell System 28

[Larry Tighe]

Mystery solved....
The capacitor on the ferro resonant power supply's 48 VDC source was bad. 
In only about 3 minutes it became dangerously hot to the touch.  The metal 
can had apparently ruptured years ago.

The supply output would start at 51 VDC and over a few minutes dropped to 
about 21 VDC.  That was the cap heating up.  This in turn raised the temp on 
the cabinet to extremely high levels.  I suspect the telco never realized 
this and put a fan into the side of the cabinet on the KSR level...the 
electronics in the base run cool.

The bad cap. was under the LESU and not at all obvious.  I built a new 48 V 
PS on the old chassis and all is cool and dependable now.

lar
www.antiquetelephone.com