Hi Bob and Chris,
Why not just stick an 8874 in it. It is electrically the same tube and plugs
in the socket. These are readily available from Eimac and Svetlana. Svetlana
is considerably cheaper from RF Parts. The Svetlana 8874s are in my Alpha 76
and have several hundred hours so far and are working out just fine.
Build some duct work around it and unbolt the heat sink and replace it with
a simple aluminum plate with a fan on the back.
This seems the obvious choice to me.
73 Steve wd0ct
----- Original Message -----
From: "Bob Marston" <k1ta@contesting.com>
To: <amps@contesting.com>
Cc: <gm3woj@talk21.com>
Sent: Tuesday, June 19, 2001 9:16 AM
Subject: [AMPS] Replacing 8873
>
> Hi Chris
>
> In the matter of locating a replacement 8873 for an SB-230 you are quite
> correct. As they have been out of production for a number of years your
> friend's chances are slim at best.
>
> If you want to change the type of tube that can be done but there isn't a
> Drop In replacement available. Based upon what is the most practical your
> friend has two choices.
>
> 1) Modify the amp for use of a 3CX-800A7/3CPX-800A7 This tube uses the
> same socket as the 8873 (SK-1900). As you stated this option will require
> some metal work relocating the socket and installing and cooling system.
> The 3CX-800 also uses a different filament voltage 13.5 volts. The big
> advantage to this tube is the increase in power dissipation to 800 watts.
> Plus the fact that this tube is readily available. The 3CPX-800A7 is
> manufactured on both sides of the Atlantic. Svetlana makes this tube also
> but I've heard reports that requires a little more umphhh to drive it.
>
> 2) The second option is to use the 8560AS. This tube is similar but not
> identical to the 4CX-250B. It is a conduction cooled tube so you can use
> the existing cooling system. It also has the a 6.3 volt filament like the
> 8873 so that doesn't need to be changed. As it is a tetrode you will have
> to make some changes there. I have seen some unorthodox circuits that
> drives the cathode, grounds the control grid and forward biases the screen
> grid. (Posted here on the Amps list some time ago) I have no idea how it
> performs.
>
> The 4CX-800A is also an option but requires substantially more work than
> the previos two.
>
> There are your choices Chris
>
> 73s
>
> Bob K1TA
>
>
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