[Amps] matching network

[Roger D Johnson]

Ray Burke wrote:

> At one time, before the GPS satellites made them redundant, there was a
> string of Loran stations along the Atlantic coast of Canada.
>  
> The workhorse at these stations was a linear, using a pair of 4CX350's,
> built by Technical Material Corporation of Mamaroneck, NY and Ottawa,
> Canada.  The Loran is gone, but the linears are still around,
> beautifully-built units, good from 2-32mhz, ideal for ham use.
>  
> Well, not exactly.  These linears can be driven to full output with only
> a few watts of drive into the exciter stage (which uses a 6CL6 and a
> 6146).
>  
> So I removed the exciter stage, and converted the 4CX350's to grounded
> grid, reasoning that now the linear can be cathode-driven directly by my
> Yaesu FT-900, which has an automatic antenna tuner.
>  
> That's where I'm at, and my question for the experts is: what kind of
> matching network at the cathodes of the 4CX-350's is recommended??
>  
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> 
Hi Ray...

  I think you are going about it the hard way! As Rich said, these tubes
are designed for grid driven service. My recommendation would be to use
a passive grid configuration. This can be realized by using a 37.5 ohm
and a 15 ohm resistance in series from the input to ground with the tube
grids connected across the  15 ohm resistor. The driver sees the 52.5 ohm
combination for a good match and tapping the tube grids down on the
resistance allows them to see the proper voltage for full output.
Mouser has 53 watt Ohmite thick film power resistors in a TO-220
package. Two of the 588-TCH35P-75 in parallel for the 37.5 series
resistor and a 588-TCH35P-15 for the 15 ohm to ground should work
just fine.

73, Roger


-- 
Remember the USS Liberty (AGTR-5)
http://ussliberty.org/