[Amps] Switching PS for filaments?

[TexasRF at aol.com]

It may be 1 in 1000 but if you are the 1 you might well think the number is  
1 in 1. After loosing the filament in a couple of 8877s and a TH347 over the  
years, I have become one of the fanatics!
 
I assume that by the time the ramped filament voltage in a 4-1000 reaches  
rated value that the cathode is ready to go. Certainly by the time you get the  
standby/operate switch flipped it is ready.
 
If we are talking about an 8877 then by all means we better be giving it  
proper warm up time but a 4-1000 or TH347? I see no cathode temperature issue  
there.
 
73,
Gerald K5GW
 
 
 
In a message dated 2/18/2007 9:33:27 A.M. Central Standard Time,  
w8ji at w8ji.com writes:


>  One problem that can arise is if the psu doesn't like 
> providing the  excess amps when you first switch because 
> the filament is cold. I got  a 5v 15A one for my 4CX1000 
> (yet to be built) amp: it won't start  with a cold 
> filament. It's possible some constructive step start or  
> voltage ramping is needed.

While being fanatical about  filament voltage in an effort to 
prevent the 1 in 1000 tube filament  failure, the same 
attitude should compel users to add length to the warm  up 
time. After all, the cathode will heat slower and won't ramp 
up in  temperature as fast.

I wonder how many people deep into the quest for  perfection 
think of that?

73 Tom  


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