[AMPS] The things you see Homebrew Amplifiers
kc4slk
kc4slk@csrlink.net
Thu, 7 Oct 1999 20:37:26 -0400
Sorry guys, but I couldn't pass this opportunity to interject here:
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.
I have a few QST's from 1954 with an Eimac advertisement on the page (the
pages were smaller then). They were demonstrating the advantages of
ceramic/glass power grid tubes (ie. 4cx150 ect) vs. glass envelope triodes
(ie. 250TH etc). The picture shows the 250TL in a lump of molten glass in an
oven while the newer style still retains it shape. I wish I had that picture
as a poster. But it was an advertisement for Eimac.
Cheers,
Mike
W3SLK
-----Original Message-----
From: Larry Molitor <w7iuv@axtek.com>
To: Bill Fuqua <wlfuqu00@pop.uky.edu>
Cc: amps@contesting.com <amps@contesting.com>
Date: Thursday, October 07, 1999 7:58 AM
Subject: Re: [AMPS] The things you see Homebrew Amplifiers
>
>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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