Ian,
They are not coaxial based and have pins, I was typing from memory and they
are 4CX250BM. They go to an HF amplifier group made by Marconi (7amp groups
mean 280 of the tubes or 40 per amp group for a total of 7KW combined). I am
not the tech. on this system and the young guy who works on them who is pretty
much on par with an apliance operator practically works for me. They use tubes
for each band is the reason for so many. They also use the same tubes to drive
pairs of the finals. Thanks for the clarification.
I have often wondered why they use such a tiny tubes and have thought
possibly the 1200VDC plate potential allows them to work over a broader range
of frequencies without being tuned but that is a SWAG.
73,
Mike
----- Original Message ----
From: Ian White GM3SEK <gm3sek@ifwtech.co.uk>
To: amps@contesting.com
Sent: Wednesday, December 12, 2007 7:51:29 PM
Subject: Re: [Amps] 4CX250 MSDS SHEET
mike kendall wrote:
>Pete,
> The only tubes I have seen with pink ceramic is the russian ones that
>I've bought off of Ebay and from friends. I have to wonder if the
>russian ones have BeO?
>73,
>Mike
>
>
>
>----- Original Message ----
>From: Pete Smith <n4zr@contesting.com>
>To: mike kendall <ke6cvh@yahoo.com>
>Sent: Tuesday, December 11, 2007 10:04:21 PM
>Subject: Re: [Amps] 4CX250 MSDS SHEET
>
>Isn't BeO ceramic pink?
>
>73, Pete N4ZR
>
>At 05:26 AM 12/11/2007, you wrote:
>>Hello,
>> We have a piece of equipment at work with quite a few 4CX250M (Mobile
>> version that is more rugged than the 4CX250R) tubes in the equipment. I
>> was asked if the ceramic portion of the tube is berrylium oxide or if
>> there is any berrylium oxide in the tubes. I am fairly certain that is
>> the case but could not find any hard data on the internet to confirm so
>> am asking the group if that is the case.
>>73,
>>Mike
"Pink BeO ceramic" is an urban legend.
Right here in 1999, "John T. M. Lyles" wrote:
>
> Thanks for the statement below, to help clarify this topic on BeO.
> The pinkish ceramic on old RCA tubes was made by a company in
> Frenchtown (NJ, NY, PA?), so was called Frenchtown ceramic.
> Sometimes there is a purplish hue to it. Svetlana has some sort of
> similar material, from another source. Manganese is in it. And yes,
> it is not BeO. BeO is present in some conduction cooled connector
> blocks on power tubes, and on the undersides of many RF power
> transistors, between the device and the bottom flange. The white
> top cap is usually alumina ceramic.
>
> Eimac stayed away from using the pink ceramic for marketing reasons.
> Technically, Frenchtown ceramic made very good tubes, and many
> of our > 3MW triodes, Burle/RCA 7835, had pink. Nowadays they are
> all white.
>From http://www.svetlana.com/docs/tubeFAQ.html [CAPITALS added for
emphasis]:
"Q. Why is your ceramic pink?
A. Svetlana ceramic power tubes are manufactured with high-purity,
high-alumina ceramic with CHROMIUM and MANGANESE additives. The
combination of chromium and manganese with high alumina ceramic results
in a true chemical bond in the metal-to-ceramic brazing process. These
additives also give Svetlana ceramic tubes their distinctive appearance.
The stronger bond allows a higher processing temperature than typically
used by manufacturers in the West. A high-temperature bake-out process
drives gasses from the internal electrodes during vacuum processing.
Clean high-temperature processing means long operating life..."
Unfortunately the svetlana.com website is long gone, but I seem to
remember that the complete FAQ also mentioned beryllium more
specifically. There may be someone here who still has that complete
document.
Mike, your other post about shipboard amplifiers using very large
numbers of tubes raises doubts: did you really mean "4CX250M"? The 250M
is a coaxial-based tube, but there is also a 4CX250BM which has the
regular pin base.
The BM fits your description much better, because it was specifically
supplied for distributed amplifiers which use large numbers of tubes. I
just confirmed that my two Eimac BMs have white ceramic. Somewhere I
also have a pair of Svetlana BMs which are pink - but that's due to
chromium and manganese.
You don't say who made the tubes that you have, but if it's Eimac, you
should be able to get a definitive statement from their product support
team:
Tel: +1 (800) 414-8823
Email: powergrid@cpii.com
--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
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