[Boatanchors] antique Philco AM/SW table radio

[Dick KF4NS]

I hope this is not off topic. I have this Philco 42-322 which is a 6 
tube ac/dc superhet using 7 volt loctals and a 35Z3 rect/50L6 audio 
amp. I did not start learning radio until about 1950 so this one has 
me befuddled. I have been able to figure out most of the theory like 
the use of the series string filaments with the large dropping 
resistor, but I am really confused by the speaker arrangement. The 
winding attached to the back of the speaker is shown on the schematic 
as a "field coil" which is in the B+ line directly off of the cathode 
of the rectifier. Also, the load resistance for the 50L6 is stated as 
around 2K but the output xfmr has a stated 240 ohm primary and a "less 
than .1 ohm" secondary. Then the schematic shows 2 series coils also 
in the secondary with one marked as .5 ohm. This is all very 
confusing.

I have replaced all the caps except the micas which tested great. I 
used orange drops except for the electrolytics for  which I used the 
Xicons from Mouser. Many of the wires had the old rubber insulation 
which had dried and cracked so I replaced the real bad ones with new 
stuff. All of the resistors tested at least or better than 10% to my 
amazement. Both IF xmfrs had totally rotted leads which were all 
replaced.

I know that I should normally replace the line cord with a 3-wire but 
am not sure if that is a good idea because I am not clear on the ac/dc 
theory. Looking at the schematic I do not see any circuit grounds 
other than the antenna xfmr, several bypass capacitors and the cores 
of the output xfmr and field coil.

I am adding a 50 ohm ICL (inrush current limiter) but cannot decide 
whether to use a polarized plug and insert the ICL into the hot lead 
or doesn't it matter? I am also adding a fuse to the ac input to 
protect the tubes, etc. in the series string in case one of the 
filaments goes open. The specs say it uses 30W so at 117V input that 
means a fast-blo of about 1/4 to 1/3A fuse. I guess I need to leave 
some slack there so the 1/3A would most likely be appropriate.

Another thing I noticed is the use of a choke to ground from the 
common cathode supply bypass capacitor. I removed the few windings of 
insulated wire from the original paper capacitor which was also rubber 
insulated wire and replaced it with a .1uh 600V choke from Mouser when 
I put the orange drop replacement in there. Is that to reduce hum in 
the audio?

Sorry for the long-winded disertation. Any help/advice will be greatly 
appreciated.
Thanks and 73, Dick KF4NS
St Petersburg, FL 33714 USA
Keep The Glow!