Thats awful lot of work. And then hope the source of tubes doesnt dry up.
Ive done a swap by sawing off the side of an 8874 (dont laugh, they "were"
cheap) and TIG welding a heavy brass plate. I forget the dimensions but it
lined up with the 8873 insulator. Since both tubes are in the same family it
was plug and play. Any SB-230 will benefit from a little bit of air on the
heat sink. That amp was used on 6M for 15 years as a portable and in a
rover, rock solid 550-600W out and is probably still in use today.
Another possibility I thought of years ago was the 8072 tetrode. It is an
8122 without the radiator and they are dirt cheap as they were used in
thousands of Motorola VHF and VHF repeaters. It uses the same socket as the
8873. Construct a radiator out of a solid brass block to attach to the
insulator.
A screen supply would have to be added as well as bias and filament
(12.6-13.6V). The screen could be taken off the HV with a voltage divider,
SS regulator and fail safe protection. Not the best way of doing it
but......
Another possibility for the adventerous would we to use a grounded screen
"super cathode driven" circuit.
Either way would use the existing swamped input and you would have to
experiment to determine the drive required. About 40W grid driven as a
guesstimate based upon my experience with 8122's in the NCL-2000.
Carl
KM1H
----- Original Message -----
From: "Bob Miller" <wb6kwt@sbcglobal.net>
To: "Amps Reflector" <amps@contesting.com>
Sent: Friday, October 12, 2007 3:59 PM
Subject: Re: [Amps] SB-230 Amp Retrofit
> Harry,
>
> Check this site out, these fellows have a couple
> of other retrofits too.
>
> http://gi7b.com/sb230/index.html
>
> Bob
> wb6kwt
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
> Behalf Of Harry Brown
> Sent: Friday, October 12, 2007 10:55 AM
> To: Amps Reflector
> Subject: [Amps] SB-230 Amp Retrofit
>
>
> I got a SB-230 Amp at a local hamfest with a bad 8873.
>
> I'd like to replace the 8873 with something affordable. Can someone point
> me
> to a conversion article on the 230 that uses an air cooled tube?
>
> 73, Harry, W3IIT
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
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