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Will Vincent st-70 upgrade

I just purchased a used beautiful Will Vincent upgraded st-70 power amp. This is my first tube power amp so I am somewhat of a novice when it comes to these units. On the top of the amp between the power supply transformer and output transformer there is a toggle switch. What does this toggle switch do? I don't want to mess with it not knowing its function.
ces4x4
newbee
4,793 posts
 
If you only have one set of outputs that switch could, alternatively to Marakenetz's comments, change the output impedance from 8 to 4 ohms ala some Cary amps. Just a WAG though. Maybe another owner will actually know.
exocet954
98 posts
 
Ces4x4,

The toggle switch is for hum control. Try in one or the other mode for least hum...I own a Vincent ST70 amp as well.
ces4x4 OP
16 posts
 
Thanks exocet954, I talked to the previous owner and he confirmed its a ground disconnect. Just out of curiousity, have you done any tube swapping? I'm currently using the kt77's and 7199's and what I think is a gz34 as it has no markings. I have a set of el34's but have not tried them. Also, what do you have the bias set at if I may ask? Thanks
rrog
1,958 posts
 
Hum control. I never would have guessed, but why do you need hum control and how does it work?
marakanetz's avatar
marakanetz
5,473 posts
 
Hah, it's simply disconnects ground if there's a ground loop similar to cheater plug.
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