At 10:20 PM 10/5/99 -0400, Bill Fuqua wrote:
> This has a muffin fan. But I guess he did not run it
>at higer powers. Glowing plates. The main problem being the
>heat conduction thru the plate lead to the seal. I'm concerned about
>cracking the seal. However, I'd like more input about this.
>I wonder if any readers have cracked anode seals on 4-400's or
>4-1000's and what they believe led to the failure.
> I have heard of holes sucked in the side of some glass tubes.
>This had to be done by radiant heat like a hot spot on the
>anode.
Sounds to me like you already made up your mind that it's no good. Why did
you buy it? Why did you ask if it was OK if you already believed it was not.
It also sounds to me like you have never run a pair of 4-400's in your life
or even have been in the same room as an operating pair. And yet you argue
the answers you just asked for.
>From the RCA tube manual for 4-xxx series tubes: "Plate shows an orange-red
color when operated at maximum CCS ratings". When operated in my functional
amp of 30 some odd years they don't even do that much with about 600 watts
peak dissapation in SSB and CW service. They do get a bit blushy when run
full bore during RTTY contest. This amp has a little 3 inch muffin fan
under the chassis producing a gentle breeze thru the sockets with Colman
lantern chimneys. My "new" 4-400 amp has the tubes mounted above chassis
with standoffs on the sockets and a 5 inch muffin fan blowing sideways.
Can't see any difference in anode color between amps when run at same power.
I broke a seal once. One 4-400 developed an intermittant grid-cathode
short. Whacking the plate cap with the plastic handle of a large
screwdriver would fix it for a while. One nite the short reappeared while I
was chasing something rare on 80. I got a little heavy handed after the
sixth or so whack and knocked the top off the tube. Only seal failure I've
ever seen.
Those pretty little finned plate caps are about useless for heat transfer
purposes. If they were glass-beaded they would be a bit better.
Glass-beaded and painted radiator flat black would make them almost wothr
the effort. The lead from the anode through the glass is not copper, I
doubt it transfers heat very well. The dissapation is from radiation, not
conduction through the plate cap. The anode needs to turn a little red for
it to getter the gas anyway.
Clandestine operations with an acytlene torch produce interesting
conversation pieces and dandy old wives tales. Try as hard as I could with
several different tubes, I could never get one to suck in from excess
dissapation. I believe it takes a concentrated electron beam to cause such
a thing. I'm guessing at that, I will bow to experts in that field as
required.
>You did not comment on the panel mounted variable. The problem
>with this is that the RF current flowing thru the PI input capacitor
>flows thru the front panel making for an excellent antenna for
>all the harmonics that the capacitor should be filtering out.
I refer back to my comment about the case being good enough if it keeps you
from being electrocuted. If that panel (and the cap) is not properly
"grounded" to the rest of the business, you will get knocked on your ass
the first time you try to tune it (or at least burn the ends of your
fingers). If you don't, it's good enough. Harmonics should be the least of
your worries with this kind of slipshod construction. Now please
understand, I would never recommend that type of construction. I think
anyone who would build like that is a jerk. But that won't keep it from
working.
Sounds like you need to dump that thing and get an ALPHA or HENRY, they are
both pretty and use lots of screws.
73,
Larry - W7IUV
w7iuv@arrl.net
http://www.axtek.com/w7iuv
Amp pix at http://207.108.137.61
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