>
>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
/\ However, with g-g config. and a transistor-output radio driving the
SB-230, a tuned input is sorely needed.
>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.
/\ No problema. Just put a small 6v xfmr. in series with the extant 6v
winding.
>The big
>advantage to this tube is the increase in power dissipation to 800 watts.
>Plus the fact that this tube is readily available.
/\ An even bigger advantage is the roughly double the peak cathode
current capability.
>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.
/\ Drive the 8560AS tetrode in grid-driven config and no tuned inputs
are needed. Screen voltage can be siphoned off of the 2kV supply with a
resistor and a zener string.
>...
cheers, Bob & Chris
- R. L. Measures, 805.386.3734, www.vcnet.com/measures.
end
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