Moto VT71: a better ballast?

[bandersen]

Any update on the better ballast project ?

[Big Dave]

We sold a prototype to a VT71 restoration client. So far, it works as designed. I will build new ballasts as we get orders. I'm not sure about pricing at this point. Email John for more information.

[compucat]

Originally Posted by Big Dave

We sold a prototype to a VT71 restoration client. So far, it works as designed. I will build new ballasts as we get orders. I'm not sure about pricing at this point. Email John for more information.

Please keep us posted on this. My Motorola 9VT1 is in daily service and a ballast replacement with cool running components is desired. I hope to do more Motorola electrostatic set restorations in the future and it would be good to know I can get ballasts.

[polyphase]

I looked at the schematic for the 9VT1, and saw that the ballast is 17A485459, same as the later VT71. All you need to do is replace the pair of 105ohm filament resistors with 10uf caps as specified in post #1 to get cool.

[Meaderon]

What voltage should the capacitors be?

[Electronic M]

Originally Posted by Meaderon

What voltage should the capacitors be?

At least 250VAC on the filament dropping caps in the ballast to be safe. The DC voltage rating should be at least 1.414 times the AC rating.

[dieseljeep]

Originally Posted by Electronic M

At least 250VAC on the filament dropping caps in the ballast to be safe. The DC voltage rating should be at least 1.414 times the AC rating.

I lean toward using cap droppers. The surge limiting of using cap droppers is a bonus.