[AMPS] 3cx800

[David B. Ritchie]

FYI --
My friends who work for Eimac and design their tubes have repeatedly told 
me that they are serious about their filament voltage specs and that if 
you are high or low, it will reduce cathode life, particularly on tubes 
such as the 3CX-type tubes (like 8877s, 3CX800s, 8874s, 8875s, etc.).  
They even told me that there was some sort of derating of life time curve 
that they had come up with calibrated in .1 volt steps.  If I were you, 
I'd make an effort to be exactly on the dime with filament voltage 
measured at the tube -- its really not that hard to do.

Have fun
Dave N7UE



On Sun, 13 Apr 1997, Robert wrote:

> Update on 3cx800 project (into mla2500).
> Tested a RS 12.6vac 3amp transformer for filament supply.
> Ran 14.5 vac unloaded.  Ran 13.05 vac into two 3cx800's
> That's close enough to the 13.5 spec (for me).  A ham that 
> regularly changes the Aplpha 8874's out to 3cx800's told me 
> about this.  ( He was a 4 - but can't recall that call)
> 
> Made the new air box and tested it with 3cx800's in place.
> The tube height is only abt half way up the muffin fan which
> is the top of the box.  It is a SMALL duct on the top half 
> of the fan into the box!  (any ideas?????)
> Air flow is there, about what a muffin can put up.
> (less air, less power).  I did go through the Rotron Fan 
> catalog and it appears for 120vac fans that model MX2A3 puts up
> the most.  It is on the bench for the next test.
> Another fan will have to be added to cool the rest of the box.
> 
> 1.  I wonder why I couldn't take the 3cx800(s) to a shop and 
> cut horizonal slots (like 8875) and run without a box????
> Certainly not going to use the full 800 watts/tube.  
> I understand the MLA2500 HV PS is about a 800watt rating 
> key down??
> 
> I would like to not use the RS transformer as it must be outboard
> mounted.  If I could find a good regulator for 13 to 13.5 VDC/3amps, could
> take the existing filament taps into a doubler and play the game that way.
> Haven't changed the timer- will manually let the tubes warm 3 minutes
> for the RF test.   Will handle those type changes afterRF test.
> -- 
> 73 Robert  W5AJ  w5robert@blkbox.com   
> 
> --
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David B. Ritchie, Esq.
D'Alessandro & Ritchie, P.C. -- Intellectual Property Lawyers
3521 E. Yorkshire Road, Pasadena, CA  91107-5432
818-683-8800 (TEL)   818-683-8900 (FAX)   dbr@alumni.caltech.edu


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