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

[Larry Molitor]

At 01:39 PM 1/13/00 -0500, Steve Bookout wrote:

>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. 

Steve,

That's just what I thought some years ago. since I saw so many cross-cooled
amps being built, I decided to de-bunk that idea myself. I built a
mono-band amp with a pair of 4-400A's. Put the sockets on a little raised
plate with about 3/4 inch clearance between it and the chassis. Mounted the
muffin fan about 4 inches away from the tubes.

The amp runs 1500 out all day, every day, CW, RTTY contests, even (ugh)
SSB. Tune ups are done full power locked key. The tubes seems to be fine.
The pins have not unsoldered, the socket springs have not turned to mush,
still full output. This particular experiment has only been running for
about 13 years, so I guess the tubes could still fail!

I am not saying this is a better way, just that it appears to be a viable
alternative even for 4-400 type tubes.

73,

Larry - W7IUV


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