Well, it does blow some air on the socket but not up thru the socket to the
seals.
In some 4-400A tubes the pins are connected by smaller conductors from the
socket and
do not themselves conduct a lot of heat. That is why the sockets and tubes
have holes
in them and the shields as well. The air is supposed to blow up thru the
holes and hit the
seals and then out the sides holes in the metal shield.
The 3-500z tube do not have the metal shield and the side flow does hit
the seals and
along with the pin cooling they stay cool enough.
You may get by anyway with the 4-400As because they will be running at
lower power and
they are running in either CW or SSB modes. But if you were running full
bore RTTY you
may have a problem.
The tubes were designed to run with the plates red 24/7 and which is
unlikely in
a SB220. This is why I was wondering if someone had some real experience.
A very interesting seal cooling mechanism is the one that was used in
the EIMAC
1000T. The tube was the same size as a 450TH but lots more power. They
provided small
metal tubes that carried low pressure air straight to the seals on the base
and the grid.
I guess they were intended to be used as a upgrade for 450T transmitters
using same sockets
and physical size.
73
Bill wa4lav
At 04:32 PM 12/6/2011 -0500, Carl wrote:
>The SB-220 cools the filament pins.
>
>Carl
>KM1H
>
>
>----- Original Message -----
>From: "Bill Fuqua" <wlfuqu00@uky.edu>
>To: "John King" <k5pgw@yahoo.com>; <amps@contesting.com>
>Sent: Tuesday, December 06, 2011 9:15 AM
>Subject: Re: [Amps] Replacing 3-500Z tubes with 4-400A tubes
>
>
> > One possible issue with the 4-400A is that it has a metal shield around
> > the glass seals on the base.
> > The cross flow cooling used in some amplifiers does not work well and an
> > additional fan
> > may be need to cool the seals.
> > Maybe someone can comment on this that have had personal experience
> > making the conversion.
> > 73
> > Bill wa4lav
> >
> >
> >
> > At 04:20 PM 12/4/2011 -0500, John King wrote:
> >>I have several very good 4-400 A tubes and have replaced a pair of bad
> >>3-500Z tubes with a pair of 4-400A tubes in a Heath SB 220 amp.
> >>
> >>I have noticed much lower resting current being drawn when keyed up. I
> >>have noticed about 200 watts less power output with 100 watts drive. The
> >>4-400A tubes are as new.
> >>
> >>I made no changes to bias or other parameter adjustment. I would
> >>appreciate the benefit of your knowledge and experience regarding the tube
> >>substitution. Thanks and 73, John, K5PGW
> >>_______________________________________________
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> >>Amps@contesting.com
> >>http://lists.contesting.com/mailman/listinfo/amps
> >
> > _______________________________________________
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> >
> >
> > -----
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