[Amps] Replacing 3-500Z tubes with 4-400A tubes

Wed Dec 7 06:34:25 PST 2011

   1500T is the only one I am missing in my collection.
I think if you really push the 4-400A to its dissipation limits
it could be a problem. Back then the max power output at best
in a continuous mode was 750 watts. And that was operating
class C in FSK or FM.
    Running full 1500 Watts continuous output today, not
likely with a SB220 running 4-400As it may be a different issue.
     I don't see much use for chimneys on these tubes as long as you
keep air flowing across the plate cap.  I found it always interesting
that the with the chimneys the fins are in the wrong direction.
They should be more like the 833 terminals for best cooling.
    By the way the, Thunderbolt, Desk KW and Invader did have
pressurized boxes to provide air flow thru the sockets, unless you
left of the chassis plate that had the air inlet hole for the fan.
Does not require a lot since you are not
trying to dissipate a kW or more as you would have to with an external
anode tube.
73
Bill wa4lav


At 09:09 PM 12/6/2011 -0500, you wrote:
>Pin cooling worked just fine on the Johnson KW using a little fan similar to
>the SB-200. No chimneys either, just a big fan blowing air on the glass..
>
>They did it again in the Invader 2000 and again in the T-Bolt.
>
>I have a Communications Concepts 46MHz amp with 4-400's that I converted to
>6M 25 years ago, same setup. Sold it to a local and its still running the
>same used tubes.
>
>Obviously Eimac gave the procedure their blessing.
>
>Im familiar with the 1000T, a surplus amp used a pair of them to modulate a
>pair of 1500T's at the NAS Olathe club station, K0NAB, in the 60's. It was
>interesting to watch the automatic start up procedure with relays and timers
>clacking away;  the HV PS was from a huge MG set. It was driven by a
>modified BC-610 when the QRM got rough (-;
>
>Carl
>KM1H
>
>
>
>
>
>----- Original Message -----
>From: "Bill Fuqua" <wlfuqu00 at uky.edu>
>To: "Carl" <km1h at jeremy.mv.com>; "John King" <k5pgw at yahoo.com>;
><amps at contesting.com>
>Sent: Tuesday, December 06, 2011 4:52 PM
>Subject: Re: [Amps] Replacing 3-500Z tubes with 4-400A tubes
>
>
> > 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 at uky.edu>
> >>To: "John King" <k5pgw at yahoo.com>; <amps at 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 at contesting.com
> >> >>http://lists.contesting.com/mailman/listinfo/amps
> >> >
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