[R-390] R-390A s/n improvement 6HA5 mixer, 6GU5 RF amp

[Larry H]

Thanks Roy.  I certainly agree about hacking up a perfectly good (or not even a perfect one) to do this kind of thing.  I thought about it for 2 seconds, then threw that out the window.  That's why when I found the parts that I needed to make a plug in tube adapter, I chose this route.  My motivation is pretty basic - in my previous homes I could put up antennas that could pull in the weak stations quite well.  I'm not so lucky here.  But, this is a real step in the right direction - my reception is much better than it was last week.  It's almost great.
Regards, Larry

      From: Roy Morgan <k1lky68 at gmail.com>
 To: Jacques Fortin <jacques.f at videotron.ca> 
Cc: Larry H <dinlarh at att.net>; R-390 Forum <r-390 at mailman.qth.net>
 Sent: Wednesday, April 20, 2016 9:51 PM
 Subject: Re: [R-390] R-390A s/n improvement 6HA5 mixer, 6GU5 RF amp
   

On Apr 21, 2016, at 12:15 AM, Jacques Fortin <jacques.f at videotron.ca> wrote:

> Hi Larry,
> Thank you for having posted the results of your experiments.
> To my knowledge, this is the first time that someone tries to substitute the 6C4 mixer tubes of the R-390A for another type of triode.

Jacques and Larry,

There was a series of articles quite some years ago, I think in Hollow State News, about replaced tube types in the first RF stage and mixer stages of the R-390A.  In both places, the new tubes were of the frame grid types, which were not yet developed when the R-390A was designed.  I don’t remember if there were any measurements presented to quantify the increased performance, but I do remember claims of increased sensitivity or lower noise and increased dynamic range after the changes.

I also remember later articles with the opinion that the improvements did not warrant the work to implement them, especially considering the fine performance of the receiver as designed, and the rareness of conditions where the improvements would make any real difference in actual performance.

I’d be glad to hear if anyone has the references.  Unfortunately I don’t have access to the articles now.

Roy

Roy Morgan
k1lky68 at gmail.com
K1LKY Since 1958