[ARC5] R-10 in the receivers.

[Mike Hanz]

I for one would be highly interested in reading your corrected rewrite 
of the offending paragraph, Brian. Being about the same length as your 
excellent warning below (with which I agree wholeheartedly), it should 
be just as quick to dash off and not take much valuable time...heh, heh...

I have no knowledge of prisoners being used for tech writing here in the 
US, though I agree some of the explanations do seem like they were 
dashed off by a harried prisoner (of work), as Don mentioned.  On the 
other hand, I'm reminded that my English boss in Saudi Arabia 
occasionally used to comment to the Aussies on the staff about the 
"distinguished convict heritage" of original Australian settlers, but I 
suspect that was not what you were referring to.  He *did* always have a 
huge grin when he said it, and it was usually only in response to an 
overreach of some sort... :-) Please don't shoot the messenger - just 
remembering an old experience that made me smile.  I know there are 
similar barbs that the Commonwealth countries have about Americans.  I'm 
reading a recent exhaustive trilogy about WWII in Europe by Rick 
Atkinson, and his research has unearthed dozens of them - some 
outrageously funny, and pretty much all having a ring of truth to them, 
as all such one-liners must to retain their humor and soften the effect.

Much more seriously, are you referring to WWII Australian military 
practice?  I assume so with the invocation of the Official Secrets Act 
but take it with the subtle humor that you (hopefully) intended.  Almost 
all of our equivalent references to formerly classified WWII information 
of that sort was declassified back in 1963 or earlier.

Agree with the comment about the pot construction.

Vy 73,
Mike  KC4TOS

On 9/24/2014 4:13 AM, Brian Clarke wrote:
> Be very careful about accepting explanations in military technical
> manuals.  During war conditions, able-bodied and intelligent people
> were occupied in designing, making and using this stuff. Very few had
> time to write explanations. The writing of explanations was often
> given to prisoners, for whom high-level education in physics and
> electronics would have been unlikely. I have found many explanations
> that read well, but in terms of demonstrating electronics knowledge,
> were pure, arrant nonsense. This explanation falls very near that
> category. The problem is that a small part of it is probably correct -
> and then the well-known psychological principle of the 'halo effect'
> takes over.
> Also, use of carbon pots in place of the original wire-wound pots will
> result in noise that the 3 uF capacitor will not remove. That 3 uF
> would be good for the noise in a wire-wound pot as the wiper moves
> from one wire to the next. But with a carbon pot, sections will
> develop that will be open circuit. You know the effect that will have.
> 73 de Brian, VK2GCE.
> Brian Clarke
> BE, MBA, PhD, CPEng, FIEAust
> MD, Clarke & Associates P/L
>
> OnTue, 23 Sep 2014 21:35:09 -0500 (GMT-05:00), Mike quoted:.
>
>   >A friend who is working on is first BC-453, which was murderfied
> before he
>   >got it, and which he is trying to get back in operation, has called
> my attention
>   >to R-10, a 360K 1/2 watt resistor which is connected between the
>   >gain-control line and B+.
>   >
>   >The table of replaceable parts describes that resistor as, "H.V.
> Bleeder to
>   >Gain Control."
>
>   It's all in the readily-available SCR-274-N manual (all versions).
>
>   From T.O. 12R2-3SCR274-2 pages 23, 25
>   ( http://bama.edebris.com/manuals/military/scr274/ ):
>
>   "Gain or volume is manually controlled by a 0-50,000 ohm variable
> resistor
>   located in the Radio Control Box BC-450-A. (This may be R-25, R-26,
> or R-27
>   depending on which control section is being considered) The cathode
> circuits
>   of the RF amplifier and first IF amplifier are completed to ground
> through R-25.
>   As this resistor is increased from 0 to 50,000 ohms, the voltage
> between ground
>   and either cathode increases, and since the grids of those tubes are
> at ground
>   potential for dc, the grids become increasingly negative with respect
> to the
>   cathodes. This results in a reduction of amplification in each of the
> controlled
>   tubes, and in an overall reduction of the "gain" of the receiver by a
> factor
>   exceeding 50,000 to 1 as R-25 reaches its maximum resistance. About
> .6 of a
>   milliampere of dc flows from the +250-volt dynamotor line though R-10
> and R-25
>   to ground. The voltage across R-25 is thus greater than it would be
> if only
>   the cathode current flowed though it, and this voltage is also less
> dependent
>   on the cathode current of the controlled tubes. In the minimum gain
> position
>   of R-25 (R = 50,000 ohms) there is a difference of potential of about
> 30 volts
>   even though the cathode current is negligible. From this it may be
> seen that
>   R-10 acts to make the control voltage developed across R-25 less
> dependent
>   upon the cathode current of the tubes being controlled."
>
>   Mike / KK5F
>
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