Re: [Amps] Heath SB-230 conversion?

["David A. Pruett" <k8cc@comcast.net>]

As others have noted, the mechanical arrangement of the SB-230 with the 
original conduction-cooled 8873 makes fitting a more readily available 
axial-cooled external anode tube difficult.

In examining the SB-230 layout, it appears to me that borrowing a common 
trick from VHF amps might help; that is, forcing the air into the anode 
area and out through the cooling fins rather than trying to force air from 
below the chassis.  While I've not laid out the design on CADD to work out 
all the details, it would appear to me that once the heat sink is discarded 
and a metal panel substituted to close off the opening, a non-conductive 
enclosure could be built around the tube (which would protrude out the 
top).  Similar construction was used in the MLA-2500 conversion article on 
the Svetlana web site.

I have a friend who owns an SB-230 with a zorched 8873, and one these days 
I'll attempt some sort of the conversion.

Dave/K8CC


At 10:40 PM 9/17/03 -0400, George & Marijke Guerin wrote:
> Eric, et. al.,
>
> The same tube with forced air cooling is the 3CX400A7/8874.  It has same
> filament, heater, socket, plate cap, etc. as the 8873 used in the SB230
> amplifier.  If you can move the socket forward a little or bump out the back
> when removing the heat sink to have the cooling fins clear the back panel it
> will fit.  This tube has a diameter of 1.64 inches, same as the 8873, but
> without the flat spot.  See Eimac page:
> http://www.cpii.com/eimac/catalog/167923.htm
>
> Alternately if there is a little more room you could substitute a 3CX800A7
> tube which has twice the dissipation.  It requires more space, as it is 2.53
> inches diameter.  It uses a 13.5 volt filament, so another transformer will
> be needed.  I am told this tube runs well on 12.6 volts, so a common 6.3
> volt transformer in series with the existing 6.3 volt supply should work.
> See Eimac page: http://www.cpii.com/eimac/catalog/16964.htm
>
> The original tube (8873) and both of the above tubes use the SK-1900 socket.
> Roton makes a 22 cfm cooling fan that is about the right size, same as a
> muffin fan, but with a 2.1" x 0.94" air output port.  Model number BT2A1.
> It is listed in the All Electronics catalog:  www.allelectronics.com
> part # CF-119.
>
> Good luck,    George    K8GG
>
> ----- Original Message -----
> From: "Eric Lowell" <elowell@maine.rr.com>
> To: "Amps@Contesting. Com" <amps@contesting.com>
> Sent: Wednesday, September 17, 2003 7:38 AM
> Subject: [Amps] Heath SB-230 conversion?
>
>
> > Folks,
> >
> > Does the SB-230 lend itself to (relatively simple) conversion to a more
> > available tube?
> >
> > Thanks, Eric (W1EL)
> >
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> >
>
>
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