Er, Elton:
Looking at the schematic of a Philco mod. 650, I see that this is a transformer operated radio, and I am sure all those ground symbols go to the chassis. There is a filter cap across the AC leads, which seems to be an .015 on each side of the AC to chassis, but a 10 uFd doesn't sound right in the slightest. Let's be really clear on this, 10 uFd and 120 Volts AC sounds like a recipe for a big bang.
Lewis
:::Hi all, I am in process of recapping this set, Reading the schematic I know this has a floating ground, which is grounded thru a 10mf cap. looking at the set I see the teminal of the 10mf is grounded. So the replacement cap the positive goes to ground? just want confirmation or am I reading this wrong?
:::Thanks
:::Elton
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::
::Er, Elton:
::Looking at the schematic of a Philco mod. 650, I see that this is a transformer operated radio, and I am sure all those ground symbols go to the chassis. There is a filter cap across the AC leads, which seems to be an .015 on each side of the AC to chassis, but a 10 uFd doesn't sound right in the slightest. Let's be really clear on this, 10 uFd and 120 Volts AC sounds like a recipe for a big bang.
::Lewis
::
:Lewis I understand the ground is chassis,I am talking about the secondary side, number 77 on the schematic that the ct of the secondary is connected to is a 10uf is it not? The can is isolated from the chassis but the 10uf teminal is grounded to the chassis. Hence my question the positive goes to the chassis?
:Thanks
:Elton
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::The center tap is the most negative point in the power supply. Capacitor 77 negative end goes to this center tap. The positive end of 77 goes to chassis ground.
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:Thanks just wanted to be sure of the correct polarity.
:Now I see that cap 71 is a 1,2,and 3 uf electrolytic, are these availible? or do I need to sub a more modern electrolytic in its place?
:Thanks
:Elton
:
Elton;
Hookay, I am with you now. The cap you are talking about is the filter for the grid bias for the output stage. Things were done this way in the old days, later they accomplished the same thing by putting a resistor in the cathode of the stage. You threw me by saying "floating ground", which in the AA5 radio means no connection directly to the chassis, but RF and AF are "grounded" through a capacitor and resistor, usually of values that the line frequency will ignore. In the case of your cap in question, the negative side is grounded to chassis, as stated above. I tend to like the newer caps, they are smaller and better than older ones. The guts of an old cap can be removed and newer, smaller, and better ones placed in the original housing, if you want the thing to look original. It's pretty easy to do, and looks good.
Lewis
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You could probably use 4 MFD @ 450 Volts for all three #71 caps if you have them in your stock. If you have to order them then do as previously recommended.
Check your chassis to see if you have the #71A 8 MFD capacitor installed near the 71? If it is there change it also.
Mitch
Mitch
Mitch
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