[R-390] The R-390 and the 6AB4

[Charles A Taylor]

----- Original Message ----- 
From: "Tom Norris" <r390a at bellsouth.net>
To: <r-390 at mailman.qth.net>
Sent: Monday, October 30, 2006 5:33 PM
Subject: [R-390] The R-390 and the 6AB4


> Another slow Monday...
>
> So I was playing around with this one R-390/URR that was in the pile 
> that I hadn't gotten around to checking out - I did the usual quick 
> check of the IF followed by an RF check and noticed "this is a hot 
> receiver..."
>
> It was easily reading it's -7  volts with .1 microvolts in, in fact 
> I  had to use an attenuator.  With no signal in, it had no real 
> audio  noise nor diode load voltage out to speak of.  Pretty 
> sensitive  compared to the other radios that I've been slowly 
> getting around to  checking. (very slowly...)  Most have been lucky 
> to meet spec at  initial check out.
>
> This one doesn't, really.
>
> The gain was because the 6C4's were subbed with 6AB4's.  With the 
> 6C4's in place, the initial reading was about 10 microvolts for a -7 
> volt reading.  So far I've not been able to make it overload or see 
> any odd signals and there doesn't seem to be any unusual 
> distortion -  which I think I should be seeing considering the the 
> mixers stages  should have a nominal gain of 2 using a 6C4, best I 
> can tell.  (In  the R-390, the mixer gain is fixed vs the '390A)
> They're subs, and they work well in most apps, supposedly, look up 
> the specs - they work *really* well here, and for folks that don't 
> want to go digging into their radios it may be a solution.  They 
> made  no difference in the mixer and rf "alinement" by the way.
>
> I'll end up pulling the RF deck to clean the geartrain and replace 
> resistors,  tempting as it is to just leave it alone and just listen 
> to it - since it works.  But, it's not to spec and the  resistors 
> keep getting, ummmm more 'resistor'-y.  Many of the higher value 
> resistors in it's brother were 100% high.  This isn't a spring- 
> chicken R-390A we're talking about.
>
> Just thought it was an interesting checkout after I finally got 
> around to it.
>
> Anyone looking for these tubes on purpose can find them under the 
> number 6664 as well.
>
> 73
>
> Tom
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Tom,

Now THAT was an interesting story.

I can't use it, but it was interesting!

I've been into an R-390 (OK, OK. Just this once: R-390 NON A) and it's 
a witch's brew of gears and decks. Kinda like putting the engine of a 
car on a hinge, and ramping it up and down to change the acceleration!

Plus, it cost the Gum'mint a fair share of Fort Knox.

No thank you, sir!

73,

Charlie

Charles A Taylor, WD4INP
   Grifton, North Carolina