[AMPS] Re:Question: input Z on class AB gnd grid pair 4-400 ??

[Steve Bookout]

Rich said regarding 4-400's:

>tuneup would, of course, be nutz.  // .  The SB-220 clearly has The 
>cooling system that produced the lowest envelope temperature.  
>
>good luck.  
>
>-  Rich..., 805.386.3734, www.vcnet.com/measures.  

For that tube, I don't think the SB-220 method is ideal at all.  It is my
understanding that due to the physical difference of the tube having the
ring with the holes in it, at the bottom of the tube, blowing air ACROSS
the tube just won't get it.
With ceramic sockets, in order to cool the tube pins as they should be you
need to blow a bit of air thru the holes in the bottom of the sockets and
up and out thru the metal ring.  I don't think axial air flow is going to
do it unless it's a lot of air, then it's loud.  Otherwise, I agree. 

I have an amp built years ago where I use a very small squirrel cage blower
to push some air up thru this path.  I don't use chimneys and use muffin
fans to cool the envelope of the tube.  A relay puts them in series with
12v during stand by and gives each a full 12 v in xmit, so it's not so noisy.

Just my .02 worth.

73 de Steve, NR4M

---------------------------------------------
Steve Bookout, NR4M (ex NJ4F)
Rapidan Data Systems

'DX4WIN...The way logging programs should be!'
Free demo at http://www.erols.com/pvander

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