The PHILCO Phorum
Strange antena terminal function - Printable Version

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Strange antena terminal function - Todd - 03-07-2013

I recaped and repaired a Philco 38-10. It works fine, except for a non-functioning short wave antena screw terminal. When I hook the 20 ft. antena wire to this terminal, it does no good. However, I get short wave reception when I hook to the AM terminal! The AM terminal also works for the AM band. Everything is conected under the chassis.
For what it's worth, I replaced the 70k ohm resistor with a 39k ohm one, as I understand Philco did after production was underway. (Philco used a 40k ohm resistor, but at 20% tolorance, I see no real difference.) The Rider publication mentions no other accompaning changes. This resistor is part of the short wave receaving circuit, but I can't see how that could cause the disfunction I am experiencing.
If a little solder got down the capacitor terminal when I attached the aforementioned resistor, could that cause such a problem? I presently have no way of testing capacidence. Now that I've got myself thinking about it, I could check that terminal for an open or a ground, but I will wait to hear what the Phorum has to say about this before proceeding further, as it is now fully assembled.

RE: Strange antena terminal function - Ron Ramirez - 03-07-2013

The same antenna terminal is used for AM and SW.

(getting out binder with 38-10 Service Bulletin to confirm) Yup...as with most 1938 Philco models, there are three screw terminals in back: RED, BLK and GND. BLK is connected to chassis ground as is GND. The RED terminal is used as the antenna if you are using a conventional longwire; if you were using a dipole such as Philco's High Efficiency Aerial which was available when the set was new, the red lead of the dipole lead-in connected to the RED terminal and the black lead to the BLK terminal.

It's resistor (11) that was changed from 70K to 40K. Yeah, 39K should be fine as a replacement.

RE: Strange antena terminal function - Todd - 03-08-2013

Checked the scematic last night when I got home. I don't have a computor there. You are 100% correct. I don't know how I missed that. I guess that's why you're "Mr. Philco".

RE: Strange antena terminal function - Ron Ramirez - 03-08-2013

Well, anyone can make a mistake, which definitely includes me. It's too bad all of the problems that crop up when fixing radios are not this easy to solve.