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

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Fucian-at-aol-dot-com>
> 
> In a message dated 4/13/02 9:16:00 PM Eastern Daylight Time, tesla-at-pupman-dot-com
> writes:
> 
> << Depends on the other circuit details.
> 
>     And there is the matter of how much current the
> 
>     filament/cathode combo can supply and the separate
>     matter of how much power the plate will handle.
> 
>     BEST
>     dwp >>
> Well the plate will handle 125watts.So thats not much current -at-3000volts.Like
> 41ma maybe.

	Thats a nominal power DISSIPATION of 125 watts, not a maximum power
input which can be several times larger.  It's easy to get efficiencies
of better than 70% in properly designed power oscillators, and 80% is
doable.  For a plate dissipation of 125 watts 70% would correspond to an
input power of around 400 watts and an output of around 300 watts. The
real clue to whether you are running too much input is the temperature
of the plate.  I've never seen a 4-125A running at high power, so don't
know the plate color at nominal dissipation but would imagine it's
probably red to orange.   Running more power (hotter plate) for shorter
periods is almost certainly safe, as some of the fellows will probably
point out.

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

Ed