[Boatanchors] Pullen Mixer (nee: Anyone Noticed)

[Drew P.]

Carl wrote:

"The thought has crossed my mind as the 6BA7 is as bad in the NC-300 as in
the 75A4 and I changed both of those to 7360's in 65 and still use that
radio.

First step is to go thru it, recap and resistors plus xtal control the 2nd
mixer/osc. Get it back to spec and then play.

Ive never owned a 300, worked on many including recently, and did have a 303 for a few years in the 90's."


I've wondered why so many manufacturers of communication equipment stayed with pentagrid mixers rather than use a triode mixer such as the Pullen.  Orthodoxy? Perhaps most of the designers had previous experience in the consumer electronics market where, for the AM broadcast band at least, pentagrid converters were the norm?

I have an NC-300 and have noted that it is a less than stellar performer on 10, even after replacing out-of-spec parts and after careful alignment.
But, yes, an in-spec unit has to be the starting point for modifications.

Is the stock LC oscillator for the second mixer in the NC-300 a source of trouble?  I have not noted excessive drift in mine.

Drew