[cparsons2391]

Hey everyone!

I have been working on a Philco 51 chassis. When I received the chassis it had a Bakelite block with what appeared to be a line to ground cap on the primary of the power transformer. The block was missing the side with the numbers on it so I had no idea what the part number was.

I replaced all other caps and bypassed the Bakelite block with the line to ground cap and everything worked great! I figured the line to ground caps were in there for a reason so I rebuilt the Bakelite block with a .0047uF safety cap and wired in the Bakelite block to one side of the primary of the power transformer.

The problem is when I bypassed the line to ground cap there was no voltage on the chassis and now with the line to ground cap I do have voltage on the chassis.

Here is link to the 51 schematic: http://philcoradio.com/tech/images/51.jpg

As you can see there is no line to ground cap on the primary of the transformer. So I am no sure if it is needed at all.

Thanks,
Cody 8)  

[Steve Davis]

Cody, if only one side of the transformer primary has a line capacitor, the voltage from the chassis to ground will read either zero or line voltage, depending on which way the plug is inserted in the receptacle. If you add a capacitor to the other side of the transformer primary, the chassis voltage to ground will read one half the line voltage no mater which way the plug is turned. Either way the current available is very low and there is no danger.

Steve

[Steve Davis]

I should add, safety cap should be used in this application. The reason is, the failure mode of an ordinary capacitor is a short, where a safety cap will fail open.

Steve

[cparsons2391]

Thanks for the  replies, Steve. Interesting Info!  I did use a safety cap. I actually ordered a large stash of safety caps simply for this purpose.