[R-390] Brought Home a R-390 Today (along With a Viking I)

[odyslim at comcast.net]

 To comment on Roy's very well written note. Sometimes the older R-390's
green gear is stored way down by the veeder root counter and was originally 
stored there. It stays in place and when needed, it is simply flipped
over. It is offset.

 Fans?  Yes! I picked up 10 micro fans 12 volt dc. I used a piece of
double sided tape to secure it. The difference is so great, one can 
actually hold a finger on the 6082's without a burn. I found my fans
on eBay. 10 for $10.00

 Good Read Roy!

Regards, Scott

----- Original Message -----
From: Roy Morgan <k1lky at earthlink.net>
To: Gary Harmon <gharmon at idworld.net>
Cc: R-390 <R-390 at mailman.qth.net>
Sent: Sat, 7 Nov 2009 04:08:45 +0000 (UTC)
Subject: Re: [R-390] Brought Home a R-390 Today (along With a Viking I)


On Nov 6, 2009, at 4:44 PM, Gary Harmon wrote:

> R-390/URR...
> Radio is blowing the 3/8 HV fuse. ...

Gary,

There are a couple of points in the radio that have not been mentioned  
so far:

- There are equalizing resistors in each of the cathodes of the 6082  
series regulator tubes (4) and in the cathodes of the rectifier tubes  
(4 more).  These are 47 ohm two watt carbon units and are most likely  
drifted high and differently in value now.  They are easy to measure  
with no module removal.  The ones at the 6082's can be measured from  
tube socket  pin to 180 volt test jack.  The ones in the power supply  
can be measured from the B+ filter cap (10 uF round paper/oil unit  
near front panel bottom) to rectifier tube socket pins. I suggest they  
all be replaced by 47 ohm square power resistors of 5 or 7 watt  
rating.  These cost little and will give peace of mind.  In either the  
rectifier or series regulator circuit, their job is to equalize tube  
cathode current.  If one or more are high, that tube section will  
"loaf" while others are working too hard.  Both of these tube types  
are expensive now.

Your radio has solid state diodes in there, and should also have a B+  
dropping resistor installed.  (Do I remember 220 ohms at 10 or 25  
watts?)

- The voltage regulator circuit includes a path to reduce AC hum in  
the B+: there is a capacitor from the regulated B+ point back to the  
grid of the DC amplifier tube, C608.  If this thing leaks, your  
regulated B+ will be thrown way off.    (C606 is screen bypass and  
needs to be good, also)  Also, there's a 1 K resistor (R625)  in the  
voltage divider in the DC amp that can be off in value and throw off  
the regulated B+ level.  (of course you need to find the short first)   
Note: the B+ regulator DC amplifier tube (6BH6) appears to be similar  
to a number of other tubes with the same pinout, but it's electrical  
characteristics are different.  So make sure the correct tube type is  
installed.

- Any misguided attempts to make the radio "hotter" by putting in a  
high gain tube in the first RF amp or IF amps should be reversed.

- If you have trouble with the calibrator, note that the crystal  
operates at one mc and the 100 kc multivibrator divides by 10 by being  
synchronized to that signal. It's possible for the multivibrator to  
divide by 9 or 11 instead, and give strange results as you try to  
calibrate the radio.

- PUT A FAN IN (or next to) YOUR RADIO.  I'll send to you separately  
the picture of a fan plate I made.  It lest  you attach a fan to the  
side of the radio next to the blistering hot 6082 tubes with existing  
screws.   A common PC power supply fan will make your whole radio run  
cooler, especially the voltage regulator section.

- The original power cord plug/socket has a ground pin and will easily  
accept a three wire grounded power cord.  DO put such a cord in  
there.  If that trips ground fault interruptors, don't be surprised  
and do NOT assume that the power line filter caps are defective.

-  If your radio has no "green gear" do not be alarmed.   You can live  
without it.

Roy



Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073
Home: 607-898-3607
Cell: 301-928-7794



______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html