Re: 4-125A, vacuum tube do's and donts

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 4/13/02 10:44:40 PM Eastern Daylight Time, tesla-at-pupman-dot-com
writes:

Matt,

It's a good idea to use a variac to supply the input power while you're tuning
things up.  If you're using a single MOT for plate and filament votlage, then
this concept won't work though.  You could use a separate filament transformer
to power the filament during coil development work, then go to the MOT
filament supply when the coil is finished and portable, and eliminate
the variac at that point.  Regarding rewiring the filament winding, I usually
just add more turns to the existing winding if there's room, rather than
removing the original winding.  Doesn't matter how you do it though, but
I'm lazy...

To measure the filament voltage without the plate voltage on the plate, 
simply disconnect the HV wire from the MOT.  

To switch the HV, you may be able to use a homemade switch of 
some sort.  The switch can be thrown by pulling a long insulated 
lever or handle.  Be sure a suitable material is used for the handle
so you don't get electrocuted.  There's an element of danger to this
if it's not done correctly of course.  There are HV relays available
too which may do the job, and are safer. 

Cheers,
John

>
> Well the plate will handle 125watts.So thats not much current -at-3000volts.Like
>
> 41ma maybe.So i dont want to let this MOT rip and then the tube melts down.I 
> managed to remove the old 3.18volt filament winding and replace with a 5volt 
> winding.PAIN IN BUTT but done.Havent tested it yet.Im just afraid of letting 
> full MOT power loose.I guess I need to get over it soonin order to measure 
> some filament voltage.Any way to switch on the plate voltage AFTER the 
> filament has warmed up?Keep in mind it will be at least 3kv to switch.Righ 
> tnow im going to just get 2 MOTs and use one for a plate source an dthe other
>
> for filament.Its just goin gto be HEAVY!!!!!I want to carry this thing around
>
> for demos.I also plan to COMPLETELY enclose the MOT's cuz I dont want to 
> die:-((((.Also, where do I get a 3kOhm 100W resistor????
>
> Matt
>
>