[Amps] Indirectly heated cathodes

[Jim Thomson]

Date: Sun, 4 Apr 2010 00:41:01 +0200
From: "DF3KV" <df3kv at t-online.de>
Subject: Re: [Amps] Indirectly heated cathodes

For the YL105x family of tubes the manufacture suggests to heat it
permanently at 3.5V.
The nominal heater voltage is 3.8V.
The heater voltage of the 4CX10000D in the Racal amps in stand by is heated
at 6.9V.

73
Peter

##  You can  operate a 4CX-10,000D @ 6.375 vac  on  TX, never mind standby.
The  procedure  we use on the  3x3  and YU-148  tubes, also directly heated,
is to pulse tune em, then  reduce the fil V, till power output  JUST  starts to drop
off by a few watts, then INCREASE fil V  by  .1 vac.    IE:  find the.. 'knee'. 
Eimac told me a few yrs back, that you can easily operate a 4x5  at  85% or less
of rated  fil V.  However, you don't want to go much more than a 15%  fil redux,
whether it's  normal operate TX mode.... or   standby.. 'dark heat mode' . 
I use a sola constant voltage xfmr [1% reg]  to  run the variac.. that in turn
feeds the fil xfmr pri.      




One of the big disadvantages of the indirectly heated cathode is it's
warm-up time. has anyone experimented with using a lower "keep
alive" voltage to allow faster warm-up when full voltage is applied?
I remember the old TV sets where a diode was in series with the
filament supply and was shorted out when the set was turned on.
Is there an easy way to determine when the cathode is up to temp?

73, Roger

##  dunno abt   Indirectly  heated tubes.  I don't think you can drop the V  very much ['dark heat'] 
I believe, even if that's  done... you still  have to wait XXX  minutes, which might be slightly less than
the  normal 3 mins.   I believe there is a very  narrow window  for  fil v on INdirectly heated tubes. 
Too low, and you contaminate the fil.   Although the  YC-156  has a 6 min warm up, Eimac tell's
me to use 8 mins. 

later... Jim   VE7RF