[Amps] 3CX800 filament voltage

[sccook1 at cox.net]

Stick a small variac on the primary and be done with it.

-S


---- Gudguyham at aol.com wrote: 
> The 3CX800 and 3CPX800 both use an odd ball filament voltage, 13.5  volts.  
> With 1.5 amps.  If you try to find a filament transformer with  that voltage, 
> it is not that easy.  If you do, it will probably be a lot of  money.  I had 
> this problem myself and wanted to find an easy solution to  it.  Many of the 
> seasoned amp builders know this, but some of the newer amp  aficionados may not.  
> A little lesson is in order here.  Filament  transformers like most low 
> voltage transformers used for AC use, have  ratings.  For example you'll see sales 
> of 12.6 volt transformers in many  current ratings, like, 1,2, 3, 4, 5 amps 
> etc amps. There is a good reason for  this.  If you take any of these 
> transformers and measure the NO LOAD  voltage, it will be somewhat higher than 12.6 
> volts. once you load it down with  its rated current rating, the voltage will then 
> be 12.6 volts.  Back to the  3CX800 filament voltage, I once bought  3 4 and 
> 5 amp 12.6 vac  transformers, I set up a test jig with a 3CX800 and tried each 
> transformer until  I found one that gave me "about" 13.5 v when connected to 
> the filament.  As  I recall the 4 amp 12.6 v transformer got me right into the 
> safe zone of  filament voltage for the tube.  A transformer of this type is 
> less than  $10.00.
> On another note, a filament transformer for a pair of 3-500z tubes is 5  
> volts@ 30 amps and a filament transformer for one 8877 is 5 volts @ 10  amps.  If 
> you tried to use a 30A 5V transformer for a pair of 3-500's on a  single 8877, 
> the filament voltage would be way too high.
> You must consider the current rating as well as the voltage  rating.
> **************Who's never won?  Biggest Grammy Award surprises of all time on 
> AOL Music. 
> (http://music.aol.com/grammys/pictures/never-won-a-grammy?ncid=emlcntusmusi00000003)
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps