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From: dsi@unccvax.UUCP (Dataspan Inc)
Newsgroups: net.ham-radio
Subject: Re: Transmitting tube cost
Message-ID: <389@unccvax.unccvax.UUCP>
Date: Sat, 14-Dec-85 11:30:15 EST
Article-I.D.: unccvax.389
Posted: Sat Dec 14 11:30:15 1985
Date-Received: Mon, 16-Dec-85 03:55:40 EST
References: <683@brl-tgr.ARPA>
Organization: UNC-Charlotte
Lines: 56

> >Most of the ceramic metal tubes are more fragile, and much more
> >expensive (I think the 8875 is on the order of $250 each, and the 8877
> >is around $500!).  Paul Young, K1XM
> 
> Anybody have any data on just what makes these tubes cost so much? The

> [WRNO] explained the length of downtime to the fact that they
> couldn't afford to stock spare tubes at $10,000 each (!) and that was
> what failed, and they had to wait for replacements.
> 
> As for ham type transmitting tubes, what contributes to the cost?

     I can believe that WRNO's final amplifier(s) cost $10,000 or more.
They are probably water cooled Eimacs which aren't really made new, but
instead are remanufactured.  This is the case with most broadcasting tubes
in the nonexpendable class.

     I'm a broadcast engineer in my spare time, and have found that spares
are not unreasonable:

     4CX250F      $67.75 
     4-400C (Amperex)   $59.00
     833A         $65.00
     845          $85.00
     4CX5000      $375 rebuilt, $875 new from Varian/Eimac

     The problem that many hams face is not the cost of "real" RF tubes,
but the cost of some "typical" ham tubes used at HF.  Four 6JS6C/6KD6
horizontal sweep tubes can eat the best part of a $100 bill.  Not everyone
has the plate transformers lying around to operate a 4-400C or 4CX250,
nor the air system sockets and chimneys required. As for the cost of the
other ceramic-metal tubes cited, try CeCo or another broadcasting tube
vendor.

    Stay away, though, from the CeCo house brand tubes (although the 833's
I have in my BTA-1E modulator are still working) as they are usually made
in countries still using a lot of 'em.  I've heard horror stories about
the Chinese inability to perform a proper pin or terminal-to-glass seal.
The 807's (made in the USSR) I had almost took out my high voltage supply
in the RCA transmitter (because the modulator grids are direct coupled
and the tube was badly shorted out of the box).

    In two Collins 831F2 FM transmitters, the remanufactured tubes have
lasted longer, according to the chief engineer of WPEG Concord, NC... much
longer. However, there probably aren't a lot of hams using a 4CX5000 (or
whatever, I think the type number is wrong - you know, ceramic-metal, bigger
than a football).

    Spares aren't that hard to come by, but when you purchase them from
the local place which carries Sams' Photofacts and that ilk, you are going
to get royally reamed.  Your best bet is a broadcast supply house for 
"real" RF tubes (not sweep tubes, however).  I don't know where one would
get 6JS6C's anymore without parting with $25.

David Anthony
DataSpan, Inc.