[Amps] 4CX250 MSDS SHEET

Wed Dec 12 07:34:52 EST 2007

Years ago, I contacted CPI/Eimac about the possible use of BeO in 
ordinary power tubes, and got the answer that the external anode/air 
cooled types did not use BeO in their construction. The only current 
production tubes using BeO were the conduction cooled types. 

My specific request was about the P290A 5 kW pentode, but the answer 
from CPI covered all their small and medium size transmitting tubes. 

The amplifier group described here fits in to the Marconi H1000 
distributed amplifier, that could be found in some early frequency-
hoppers and countermeasures systems. Also, British coastal radio used 
such amplifiers in some MF telephony and radio-telex installations.

73/

Karl-Arne
SM0AOM

----Ursprungligt meddelande----
Från: ke6cvh at yahoo.com
Datum: 12-12-2007 13:15
Till: <amps at contesting.com>
Ärende: Re: [Amps] 4CX250 MSDS SHEET

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 at ifwtech.co.uk>
To: amps at 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 at contesting.com>
>To: mike kendall <ke6cvh at 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 at cpii.com

-- 

73 from Ian GM3SEK        'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
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