Zenith 9S262 antenna issue - Printable Version
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Zenith 9S262 antenna issue - NostalgiaRadioTime - 01-30-2021
Totally recapped the chassis, replaced the out of tolerance resistors, with all strong tested tubes and the radio plays but with low sensitivity. No change in volume or signal strength by touching the antenna terminal, and only very slight eye tube movement (yes, the 1 meg resistor was changed). The RF coil was replaced as one section was open.
Here's what I've found:
No change in signal strength moving from the local to distant position on the off/on control (but did verify the switch itself is working and grounds out on the distant position).
The entire chassis is very sensitive...if I touch the chassis, the volume drops some.
The 6K7 RF tube is not conducting. I get zero volts on the plate (pin 3). 92 volts on pin 4
Antenna primary measures 22.4 ohms across the ANT to GND terminals. I get two ohm readings across the terminals of the ANT coil, but measuring across it I get 1.5 meg ohms which seems suspect.
I get 262 volts on the plate of the 6L7 & 94 volts on pin 4
If I connect my external antenna to the grid cap of the 6L7, bypassing the 6K7 RF tube the radio plays normally on all bands with strong sensitivity. Eye tube functions as it should but still no change in signal strength from local to distant position. The chassis also is no longer sensitive and volume doesn't drop if I touch it.
If I connect my external antenna directly to the plate pin of the 6K7 RF tube the radio also plays strong and the same as it did by connecting the antenna to the grid cap of the 6L7 tube. Again, the eye tube works as it should but no change in signal strength from local to distant. The chassis also is no longer sensitive and volume doesn't drop if I touch it.
It seems to point to an open section of the ANT coil but if anyone could give me any other possible causes to the zero plate voltage on the 6K7 RF tube and the lack of response from the ANT terminal please let me know.
Thanks. Here are the schematic pages for reference:
RE: Zenith 9S262 antenna issue - morzh - 01-30-2021
I had the same problem.
My RF transformer that goes to the plate of 6K7 RF was open.
RE: Zenith 9S262 antenna issue - NostalgiaRadioTime - 01-30-2021
Are you calling the detector coil or #2 on the schematic the RF transformer? That wouk would make sense because the primary side of the detector coil goes right to the plate of the 6K7 RF tube. Did you rewind your coil?
RE: Zenith 9S262 antenna issue - morzh - 01-30-2021
Yes #2 coil Yes I rewound it; I thionk it was 2 or 3 turns for the primary.
See if the plate voltage is there on that tube first.
The radio worked fine and tuned, but then I realized the Local/Far switch did not have any effect. Then I touched the antenna - no effect.
The rewinding was easy - took me less than 1/2 hour with the desoldering, extraction and the rewinding.
RE: Zenith 9S262 antenna issue - NostalgiaRadioTime - 01-30-2021
You didn't happen to save your notes for the coil? I'm getting more open readings across the terminals on that coil than I am actual values.
RE: Zenith 9S262 antenna issue - morzh - 01-30-2021
No. I don't even think I ever took the notes. There was an open primary of 2 or 3 turns, nothing really to write about.
But do make sure you have opens first. A good indication of the open primary obviously is the plate voltage. See if it is in range.