Does anyone else have a slow drift problem with their Hull Hartley? I was looking at mine and spotted something I wanted to check into.
These two resistors are in the circuit to provide a ground point for cathode keying, but there is an alternative. I have a center tapped 7.5 V filament supply. I can remove those two 40 ohm resistors and just key the filament transformer center tap. The heat source will be removed so my Hartley should now stay on frequency better.
*** clock ticks while solder smoke rises ****
I did before and after standby drift measurements. After tuning on the rig I checked the transmit frequency every 30 seconds for 15 minutes. Key down was only long enough every 30 seconds to get a transmit frequency readout. I had no load connected and the plate current was about 18mA with 300 volts B+.
Was is worth it?
*** Now drums rollllll ***
On 80 meters I found that the original Hull design drifted about 2KHz from a cold start while the modified version drifted about 500Hz. That's good but both took about 15 minutes to settle down. With both versions I still have to be careful about jumping on the air right after power on. I saw no significant change on 40.
But two parts were eliminated along with some amount of power on drift, both good things.
If I were starting out now building my Hull Hartley and I had a center tapped filament transformer I'd make this change. If I already had my Hull Hartley up and running, I'd probably let it be.