[R-390] R-392 audio improvement=super, can R-390 audio be improved?

[Roy Morgan]

On Apr 4, 2015, at 11:33 AM, Frank Hughes <fsh396ss at gmail.com> wrote:

> … Is there any way to obtain a similar audio improvement for the R-390?

Yes, there are many ways.

There seem to be two methods to get *greatly* improved audio from the R-390A and one also applies to the R-390/URR (the “non-A”).

1) The Kleronomos Audio Mod:
This mod was published by Bill Kleronomos, KD0HG.  It involves rebuilding the entire audio section of the receiver with new audio tubes (6DJ8 and 6360) and output transformer.  The Line Audio output tube is changed to a 6AH6.  The whole thing was published in Electric Radio - see references list below.

A packet of information that details the modification was made available by Thomas Bowes, KK8M entitled 
"To: All R390A Audio Modification Requestees”.  It appears that Tom made this packet available for $3 for a time.

2) A no holes, no solder, no modification method is to couple the audio from the diode load terminal on the rear of the radio out to any suitable “hifi” amplifier and speaker.  A modest capacitor to block the diode load DC from the amplifier and a bit of shielded wire is all you need.  One Ham Radio magazine article (Nov, 1975, Collins R390A modifications) suggests .05 uF. You can just twist the wires together and never heat up a solder iron.   This bypasses all the R390 audio section and gives you as much power and fidelity as your external system has.  Volume control is at the external amplifier.

Other mods have been published.  Here are some:

1) Jan Skirrow's Tek Talk 4 “Improving the R-390A Audio Response””

http://www.skirrow.org/Boatanchors/TechTalk4.pdf

2) Here is a list of references I found posted to the R-390 list by Richared MC Clung:

________________
Date: Thu, 28 Apr 2005 19:41:14 -0700 (PDT)
From: "Richard M. MC Clung" <wa6knw at sbcglobal.net>
Subject: Re: [R-390] Re: kleronomos audio mod
To: R-390 LIST <r-390 at mailman.qth.net>

OK, here's some R-390A audio related ER articles.
ER 42  OCT 1992      Real Audio for the R-390A
ER 94  FEB 1997 PG34 Real Audio for the R-390A, Revisited
ER 181 JUN 2004 PG28 Simple audio for the R-390A
ER 181 JUN 2004 PG46 Audio Circuit Design in the 
                     R-390 Receiver Family 
ER 183 AUG 2004 PG7  Cheaper and Simplier Upgrades for the R-390A
ER 186 NOV 2004 PG30 AN Audio Filter Modification for the R-390A
RICH  WA6KNW

...
The issues were:  Real Audio for the R-390a  Oct 1992
			Real Audio for the R-390a Revisited Feb 1997
			Simple Audio for the R-390a  June 2004 
If you're going to do the Kleronomos mod, you should have both of the first
two articles.  The Simple Audio article stands alone.  

Dan
____________

3) Another post to the list tells of a simple change:

From: "Tony Casorso" <canthony15 at msn.com>
To: <R-390 at mailman.qth.net>
Date: Sat, 16 Feb 2008 19:45:25 -0700
Subject: [R-390] R-390a Audio Improvement

Hi everyone,

I just wanted to my experience with the R-390a audio out here for informational purposes. I was unhappy with the audio. I had made the audio deck cap changes that Chuck Rippel recommends to improve audio and I was still unhappy. Finally I removed the diode load link from the back of the set and connected my audio generator to the inbound side of the link. Monitoring the line out with my scope I saw that the low end rolled off about 3db between 600 and 700 Hz. This is way higher than the published audio curve. I checked all caps and resistors in the audio deck and everything was fine. Finally I decided to replace C549 at the limiter output in the IF deck with a .1uf  (it was .01). The audio improvement was dramatic. The .01 cap had already been replaced by me with a brand new mylar back when I got the receiver. The low end rolls off now between 100 and 200Hz.

Tony


4) The “Chuck Rippel” changes he suggests are to change some of the capacitors in the audio deck.    (Change C604 and C605 to 0.022 or larger.)



Roy

Roy Morgan
k1lky68 at gmail.com
K1LKY Since 1958