Using 140 volts makes a huge difference in performance. However you
will probably need to retune the primary frequency lower if you use 140 volts
due to the greater spark loading. Otherwise you won't get the full
advantage. I wouldn't worry about the MOT secondary, I've never seen
one fail. You should be able to get 22" with no trouble.
John
-----Original Message-----
From: Steve White <steve.white1@xxxxxxxxx>
To: Tesla Coil List <tesla@xxxxxxxxxx>
Sent: Tue, Jan 30, 2018 8:28 am
Subject: [TCML] VTTC MOT input voltage
I recently finished my 883A VTTC. With 120 volts as input to the MOT, I am getting 17" sparks with staccato drive. The coil is based on Steve Ward's schematic. Although I am satisfied with the performance I am wondering if I can get a little more. Steve Ward reports 22" sparks. The tuning on my coil is perfect, at least to 1/2 turn accuracy on the primary. The resonant frequency is 361 Khz. Construction quality is high with short lead lengths in the primary circuit. One difference that I did see between mine and Steve Ward's is that I am only using 120 volts as input to the MOT from the variac while Steve Ward seems to be using 140 volts. I could change my variac taps to get 140 volts instead of 120 volts but I am concerned with over-stressing the MOT secondary.
My question is this. Will 140 volts as input to the MOT make a significant difference in spark length? Will 140 volts over-stress the MOT secondary?
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