Motorola VT-71 (TS4H)

[fox_rivers]

Originally Posted by polyphase

I'm delighted you chose to use the cap balast I described back in Nov 2010 for your project. They are still working great for me.

For best results, it may be necessary to tweak the 30ohm resistor lower to get correct filament voltages. This is due to normal tolerances of the caps.

This is easily done at the socket, by connecting a 2w resistor of between 100 and 300 across pins 1 and 6. You can always change out the ballast R later with the newly established value.

Note: To get stable filament voltage measurements, you need to wait at LEAST 5 minuets from a cold start.

I really liked the idea of the soft start as well as it looking original. I appreciate the tip and the build design.