[Boatanchors] National VHF Receive Converters

[manualman at juno.com]

There were two versions of the 6 meter converter. There was the 4 tube
version, model NC-300C6, and there was the 2 tube version, model
NC-300C6A. I did not check the 2 meter and 220 MHz versions in each
manual to see if there were any differences in design or parts.
Obviously, alignment and parts list of both 6 meter versions are
different. The 4 tube 6 meter converter also has a National service
bulletin written against it.
Both manuals are listed on my site.

You asked:
> 1. Which version came first?
NC-300C6 

> 2. Which version has the best performance?
You would have to check the front end tube specs (transconductance, gain,
etc.). I bet the 6CB6 might have some higher gain and a lower noise
level.

>3.  Any clue why there was a change?
Probably main reason was cost reduction. With the 6 meter 4 tube version,
1/2 of the 6U8 wasn't even used. Change some tubes to reduce tube count
and drop a bunch of parts; alignment also gets easier.

Pete, wa2cwa
www.manualman.com

On Fri, 31 Jan 2020 10:57:45 -0600 Brian Harris via Boatanchors
<boatanchors at mailman.qth.net> writes:
> 
> I have some National VHF receive converters which have me puzzled. I 
> have two 2 meter versions (NC-300C2) and have no questions about 
> them. However, I have three 6 meter versions (NC-300C6) and two of 
> them have two tubes (6CB6/6U8) whereas a third one has four tubes 
> (6BZ7/6AK5/6AK5/6U8) just like the 2 meter versions.  A friend also 
> has one of the four tube 6 meter versions.  Information is available 
> for the two tube versions but not the four tube version. My 
> questions are: 
> 1. Which version came first?
> 2. Which version has the best performance?
> 3.  Any clue why there was a change?
> 
> Thanks for your time. 
> 
> Brian WA5UEK