[ARC5] Triode mixer mod

[Kenneth G. Gordon]

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