Having recently completed my 833A VTTC based on Steve Ward's schematic, I am getting 19" sparks with staccato which is satisfactory but I think there should be a little more. I have a very large MOT now installed. I see very little difference in spark length when going from 120 volts to 140 volts on the variac. The tuning is within 1/2 turn accuracy on the primary so I know that is not the problem. The resonant frequency is 361 Khz. Connections are short and thick. What I suspect is that my MOT is saturating above about 120 volts.
The MOT that I am currently using is quite large and is probably from a 1100 watt microwave oven. I have another MOT which has 50% more iron in its core that shouldn't saturate as easily. It also appears to have more windings on the primary and secondary. It is from a very old Amana Radarange circa 1975. I would like to try this MOT out which leads me to my questions. Does anyone have any information on this MOT? Here is what I know about it:
* Dimensions are 145 x 108 x 72 mm
* The are a total of 7 terminals: 2 are for the filament, 2 are for 120 volt power, and 3 are on the HV side
* There appear to be no shunts
* The core is not connected to the HV secondary
* It is made by Advance, the model is AC-180, the catalog number is 09-123-18
My question concerns how to connect the 3 HV terminals. 2 of the HV terminals are spade lugs only 1/2 inch apart. The 3rd terminal is a wire coming right out of the secondary. When I measure the resistance between the 2 spade lugs, I get about 3 ohms. The resistance between the wire coming coming from the secondary and either of the 2 spade lugs is about 67 ohms which seems correct for a HV secondary. I thought that the 3 terminals must be for a center-tapped secondary but the ohmmeter readings say no because of the very low 3 ohm resistance between the 2 spade lugs. It almost seems as if the 2 spade lugs are connected but I would think the resistance between them would be essentially zero and not 3 ohms. I think the 2 HV leads to use are the wire coming from the secondary and one of the spade lugs. I don't know what the other spade lug is for. I assume that since the core isn't connected to the secondary that I must ground the core and one end of the HV output myself.
So, in summary, here are my questions:
* How do I use the 3 terminals connected to the HV secondary?
* Has anyone ever seen a MOT without shunts? Maybe they did things differently back in 1975 when cost wasn't as much of an issue.
* Does anyone have any data on this MOT?
I have searched extensively on the internet for info about this MOT but I can't find anything. Any information about this mystery MOT would be appreciated.
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