Antennae not making a big difference. Why? - Printable Version
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+--- Thread: Antennae not making a big difference. Why? (/showthread.php?tid=5743)
Antennae not making a big difference. Why? - TheGorper - 01-11-2013
On a Philco model 91 type 126:
The antennae being connected or not connected doesn't seem to make a huge difference in receiption, but placing my hand over the coils on the set in and around the detector tube and coil does.
I have a 25' wire running out a window and across my deck outside.
I also have a low hum that is always there and sounds like a 60 Hertz low hum. AC? How much hum is normal for these sets? I will try to record and post the record as an attachment here.
Notes:
1) I have moved the set to an area of the house with low interference from other sources and tested this with a modern AM radio.
2) Have replaced the 10K ohm resistor 21 with a 7.5K ohm and baked my coil per Ron's recommendations (see my other post in Electronic Restoration. This has fixed the problem with the set cutting out and ceasing to work at the ends of the broadcast dial. It now works all across the dial.
Thanks for all the help from everyone so far. The set now picks up most stations in the area well and many clear channels from far away at night.
WCBS at 880 in New York for example. I am in North Carolina.
RE: Antennae not making a big difference. Why? - TA Forbes - 01-11-2013
Problem sounds like it's in the antenna/RF section of the set.
RE: Antennae not making a big difference. Why? - Ron Ramirez - 01-11-2013
+1 what Tom (TA) said. I would look in the antenna and RF sections first. Most likely, a defective coil. Philco sets of this time period are notoriously bad for having coil troubles.
RE: Antennae not making a big difference. Why? - Phlogiston - 01-11-2013
Open antenna coil - easy test - use your VOM, check from the antenna term to the chassis ground. It should be a few ohms.
RE: Antennae not making a big difference. Why? - TheGorper - 01-17-2013
The Antennae coil on this 91 (part #2), appears to have a magnetic wire wound around the outside of the form and a little small coil that the antennae connects to (25 ohm) that appears to be wound inside a small disk at the top of the coil assembly. This 25 ohm coil appears to be wound with a cloth covered wire with three tiny strands inside.
Am I right that the 25 ohm coil is just sitting at the top of this assembly? Or is the magentic wire wound over the cloth covered wire, with the wire terminating in that disk at the top?
Anyway, I found that one of the very fine cloth covered wires had been clipped by a mouse inside the coil, where it ran down the inside of the coil down to the lug. I was able to tin the three ends of the cloth covered wiring and solder on a fine piece of enamel coated magnetic wire and reconnect it to the lug again.
The coil looks brand new with no green discoloration at all, so for now I am going to try this out and see how it goes. Unless you guys tell me I am crazy to be doing this. I can pull and rewind the coil in necessary.
I have an open winding in my Detector Transformer (part #12) on the 4.5 ohm side of the transformer that I still need to address.