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

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

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

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 125 watts.  So thats not much

>current -at-3000volts.  Like 41ma maybe.  So i don't want to

>let this MOT rip and then the tube melts down.


	Power tubes, especially, may have the ability to
	deliver more current from the cathode/filament than
	can be handled by the plate continuously (TV Set
	Horizontal output tubes were noted for this:
	lose the grid drive, the tube goes to 'full on'
	and dies, quickly.)  I'm not familiar enough with
	the 4-125 to know what the risks are, there.

>I managed to remove the old 3.18volt filament winding and 

> replace with a 5volt winding. PAIN IN BUTT but done.

>Haven't tested it yet.  I'm just afraid of letting full MOT

>power loose.  I guess I need to get over it soon in order to

>measure some filament voltage.


	One might measure the filament voltage with HV not
	hooked up yet...  Can't think why that would be
	a problem.

> Any way to switch on the plate voltage AFTER the filament

>has warmed up?


	As a one-time, operation, cf above.  For routine
	operation this IS done in Really High Power work,
	usually using a separate transformer for the plate (B+)
	supply, switched on the line side...

> Keep in mind it will be at least 3kv to switch.


	Admirable attention to detail.  cf above for one time
	start up tests.  One might put in a _long_ fusible link
	of light wire, (so it blows open if something is wrong:
	leaving enough gap to interrupt the 3KV).  Should be
	protected/boxed in, so the fuse wire frags do not
	create problems.  (yes: It shouldn't blow.  But If It
	Does ....)  No guarantees.

>Right now i'm going to just get 2 MOTs and use one for a plate

>source and the other for filament.


	OK:
	Switch the _primary_ side of the one supplying plate
	power: 110V at whatever A.

>It's just going to be HEAVY!!!!!  I want to carry this thing

>around for demos.  I also plan to COMPLETELY enclose the MOT's

>cuz I don't want to die:-((((.



>Also, where do I get a 3kOhm 100W resistor????


	That may take some finding...