Emerson question - Printable Version
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Emerson question - Phil27 - 09-06-2024
http://www.nostalgiaair.org/PagesByModel/795/M0004795.pdf
I am working on an Emerson 131am and was wondering why someone has attached a wire to the 6A7 tube grid cap. It appears to act as the antennae. There is no external antenna connection on the radio.
The radio works but needs an alignment because it picks up the same station in more than one spot on the dial. I’m new to this hobby and am not sure whether to leave it or where it should go if I have to relocate it.
All advice is always appreciated.
RE: Emerson question - morzh - 09-06-2024
It is possible that the antenna coil is open.
It is also a known effect that the cap of the pentagrid, if touched, will act as an antenna. Which is still not a cure for open RF coil.
RE: Emerson question - RodB - 09-07-2024
Mike is right. The only parts between the grid cap and the antenna are the band switch and the antenna coil. One or both could be open, preventing signals from getting to the 6A7 grid. If the coils are good then maybe the switch needs some Deoxit.
RE: Emerson question - MrFixr55 - 09-07-2024
If the antenna coil is open, this may also be the reason for the ability to pick up the same station on 2 different points on the dial, especially if the wire antenna directly on the tube cap is used and the secondary of the antenna coil or the band switch (located on the rear apron of the chassis) is also open.
Please note that the antenna connects to the primary of the antenna coil through a capacitor and there is no ground connection as is traditionally found on sets that do not have an internal loop antenna. This is because this is a "hot chassis" transformerless set. Usually on later AC-DC sets, the chassis was connected to the power line, heater string "A" return and B- through a cap or cap and resistor. However, on this set, the chassis is directly connected to power.
Worse yet, the power switch is between the chassis and one leg of the power line, making the chassis, control shafts and any screws protruding from the bottom of the cabinet electrically "HOT" if this leg is connected to the hot leg of power and the switch is on or if this leg is connected to neutral and the power switch is off, making the chassis hot through the heater string which is a very low resistance when the heaters are cold. This makes for the strong possibility of a dangerous or fatal shock! (At our age, the tickers are not as strong as when we were stupid kids.) I strongly suggest using a polarized plug on this set and rewire the set so that the switch is on the hot side and the chassis is directly connected to neutral. This may or may not increase the hum level depending on how well the switch and volume control are shielded, but it WILL make the set safer.