[ARC5] Triode mixer mod

[Dennis Monticelli]

Ken,

I will check that out.  The plug-in feature is appealing.  No doubt some
tracking calib would be in order.   I have found that different 12K8's do
affect the tracking.

The improvement in MDS is about what I would expect going from a early
pentagrid to a modern set of triodes.

Dennis AE6C

On Fri, Oct 24, 2014 at 10:12 AM, Kenneth G. Gordon <
kgordon2006 at frontier.com> wrote:

> Gents:
>
> I have been in correspondence with a very competent ham in Europe who
> contacted me about a modification to the 12K8 mixer, which had been
> developed back in 1970 by someone in Missoula, Montana.
>
> This "mod" is a fairly simple, easily reversible, plug-in mod using a
> 12AT7 on
> an octal adapter. I have had it published on my website as a PDF for some
> time if anyone is interested. It is simply a dual-triode mixer/HFO, and
> not a
> "Pullen" mixer.
>
> Here are his results:
>
> "My unmodified BC-455 has got an MDS of -113 dBm whereas the one with
> the 12AT7 mixer modification has one of -121 dBm. Measured with R&S
> (Rhode and Schwartz) sig gen and HP true RMS voltmeter."
>
> This is a substantial difference.
>
> As he pointed out to me, this would not really make a noticeable
> difference in
> normal operation at frequencies below 10 MHz due to normal band noise,
> but it is certainly interesting, and IMHO, is applicable to other
> receivers which
> use very noisy mixers. The advantage in my opinion is that it is a
> "plug-in"
> mod.
>
> Ken W7EKB
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