On Sat, 20 Mar 1999 00:25:04 +0000 "Ian White, G3SEK"
<G3SEK@ifwtech.demon.co.uk> writes:
>
>Richard W. Ehrhorn wrote:
>
>>Eimac engineers referred to the cause of the flashovers as
>"barnacles," but
>>your description is much more descriptive.
>
>I've heard of both gas inclusions and surface imperfections that
>might
>be the same as Eimac's 'barnacles'.
>
>>These flashovers usually
>>occurred very early in tube life - more often than not during factory
>
>>checkout of the amplifiers - and were self-clearing after two or
>three
>>flashes. We also experienced frequent new-tubes-in standby flashovers
>in
>>early 8877s and 8874s through the late 70's, but in the last 15 years
>or so
>>they seem much less common.
>>
>Whatever the cause, improvements such as pure, gas-free metals and
>better processing can certainly help.
>
>
>>Proper fault current limiting
>>resistors tame the phenomenon to the point that many times the plate
>
>>overcurrent relay or breaker doesn't even trip.
>
>I think that's the main point: don't worry too much about the reason
>why, but do expect that it will happen, and protect accordingly.
AMEN !
On a voltage rating note:
I recently had a long chat with K1FO of both amp and antenna fame and
found out something interesting.
He is using 3CPX800A7's in his 1500W + 70cm and 2M amp products. Come to
find out the pulse version is not the same as the regular type.
According to Steve the CPX has a more highly polished grid structure plus
there is an additional .070" added to the ceramic insulator between the
anode and grid ring.
Those additional features allow him to feel comfortable when running
2700V on 70cm.
Knowing how conservative Steve is I wonder how far the CPX can really be
safely pushed?? 3000V @ 800ma for 1500W per tube at HF maybe??
73 Carl KM1H
>
>73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> 'In Practice' columnist for RadCom (RSGB)
> http://www.ifwtech.demon.co.uk/g3sek
>
>--
>FAQ on WWW: http://www.contesting.com/ampfaq.html
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>Search: http://www.contesting.com/km9p/search.htm
>
>
___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|