[R-390] manual comparisons

[Bob Camp]

Hi

There's a long story about this. I forget the exact details and am to 
lazy to look it up.

Bottom line is that the 6C4W seems to work just fine. None of the field 
changes in the Y2K manual seem to directly impact the 6C4's so they 
didn't change the radio any to make them work.

Since the 6C4's are being used as a mixer the normal things you would 
do to make a "super tube" version (more gain, higher linearity) 
probably are not going to make a super mixer. The conversion gain with 
the 6C4W may be a bit lower than a 6C4. If so it's not enough to 
significantly impact the sensitivity of the radio. The one thing that 
would really be an issue would be if the 6C4W has worse overload 
performance. We check measure sensitivity all the time. We don't seem 
to do many overload (third order) tests.

	Take Care!

		Bob Camp
		KB8TQ

On Jan 2, 2005, at 8:04 PM, Scott Bauer wrote:

> I was reading my 1956 Army R390-A manual and is says not to substitute 
> type 6C4W for a 6C4. It is written that the differences in 
> characteristics are such that the type 6C4W will
> not operate properly in the receiver. OK...
>
> What changed between 1956 and 1970?
> My Navships 1970 manual lists the 6C4W as the tube to use.
>
> Scott W3CV
>
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