01-30-2021, 07:11 PM
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:
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:
Greg V.
West Bend, WI
Member WARCI.org
