20-12-2023, 10:52 AM
(This post was last modified: 20-12-2023, 10:53 AM by Mike Watterson.)
Note that even a 10:1 scope probe can detune even AM IFTs, never mind 10.7 MHz.
The 75V changed to 95V on g2 with resistor change suggests the EF41s are OK.
Best idea is to unplug ECC85 and use 10pF and 100k in series to ECC85 mixer/osc section anode and measure ratio detector volts on the cap there as you slowly sweep from 10.1 to 11.3 MHz (or wider) and plot graph. Either by hand or entering into spreadsheet. Use as low a drive level as will give a reading at 10.1 MHz.
If the cores are so stiff then it's unlikely they have drifted or been twiddled. At least it goes, so you don't want to damage a core. Sometimes I'll let the cores soak in WD40, but that only much helps with hard wax.
The 75V changed to 95V on g2 with resistor change suggests the EF41s are OK.
Best idea is to unplug ECC85 and use 10pF and 100k in series to ECC85 mixer/osc section anode and measure ratio detector volts on the cap there as you slowly sweep from 10.1 to 11.3 MHz (or wider) and plot graph. Either by hand or entering into spreadsheet. Use as low a drive level as will give a reading at 10.1 MHz.
If the cores are so stiff then it's unlikely they have drifted or been twiddled. At least it goes, so you don't want to damage a core. Sometimes I'll let the cores soak in WD40, but that only much helps with hard wax.
