"cpstelecom.co.uk" wrote in message
...
Hi,

I need a 8873 tube for my heathkit linear, none of the usual UK dealers
have
one in stock. I have found a few suggestions to mod the amp to a forced
air
cooled tube but I hate the sound of fans in the shack.
--

Steve H

Remove the spam to reply.


Steve -

The 8873 (the conduction version of the 8874 triode) is rare (no longer in
production) and usually premium dollar when they do appear. The only other
conduction (not forced air) tube that MAY be adopted to this design is one
of the 4CX250 family of tubes that are still in production

The 8560AS (or Eimac 4CS250R), Motorola used this tube in its Micor base
amplifiers for a number of years. The prices for surplus tubes are $75 to
$100. Photo of Motorola amp:
http://www.uslink.net/~jcomm/2Mamp.html

It is a tetrode, instead of the triode 8873 (Mullard YL-1321 may be
equivalent; I have seen Y799 and Y808 in UK to refer a similar tube)
http://www.cpii.com/eimac/catalog/80006.htm

There is also VERY GOOD news that Svetlana is making an 8560AS (so tube
supply and production is much better)
http://www.svetlana.com/docs/products/metal/8560AS.html

Index
http://www.g8wrb.org/

There has been a fair amount of discussion about conversions of the SB-230
amplifier (e.g. using Russian GI7b triode; standard 8874 conversion) - but
most of these have been extensive modifications for forced air. I do agree
with you that if you are going to convert this amplifier - stay true to the
quiet operation (no fan) desired by original design.

I would recommend a proper control board, such as Ian White's (G3SEK)
Tetrode Boards (2)
http://www.ifwtech.co.uk/g3sek/board.../tetrode-2.htm

Of course a 6 meter or 2 meter conversion could occur at the same time
http://www.geocities.com/PatBillDavis/Amplifiers.html

w9gb