[ARC5] 10 meter BC-454 - screen voltage

[David Stinson]

----- Original Message ----- 
From: "john rose" <brokenthumb at live.com>
Subject: Re: [ARC5] 10 meter BC-454 - screen voltage


> ...It is designed to run on 24 volt B+ and is loaded with tubes 
>designed to run at this level (26A6, 26C6, 26D6 etc)....
>Will the tube really run at that B+? ....

I routinely test Command Set receivers in 
completely "stock" condition and run them for hours 
on 24 VDC B+.  
Sensitivity is a little down and audio is headphone level
( I use an amplified external computer speaker - 
 cheap as dirt at yard sales ).
I'm not trying to work DX with a Command Set receiver,
so a minor reduction in sensitivity is no issue.  In fact,
they run cool, stabilize faster and the noise floor is better.
I've run some for years this way and never encountered
a "downside" I considered significant.

Many of us run them a varying amounts of reduced B+.
Some make changes to the screen voltage divider
but I've never had a need to do this.
I have found a "breakpoint," however:  
Something changes between about 75 and 110 VDC.
I tried 90 VDC and the receivers just sound "crummy."
Audio is distorted.  Down at 24-28 volts and above 
about 150, they sound fine again.
One of you Smart People should tell us what's going on.

In fact, I've run an entire stock SCR-274N 
on straight 28 VDC for fils and B+.
It was QRP TX power and headphone audio,
but it worked spendidly.   
Got to hand it to those A.R.C. engineers.

73 DE Dave AB5S