[ARC5] 10 meter BC-454 - screen voltage

[Scott Johnson]

These tubes are cognate versions of others, and, in the case of the R-392,
extra gain stages are employed (over the R-390) to provide adequate gain at
24-28 VDC B+.  There are other equipment that use the same techniques, such
as the ARN-6 radio compass, the BC-1206  range receiver (Loctals), and the
ARN-32 marker beacon receiver (subminiatures).

Scott W7SVJ

-----Original Message-----
From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On
Behalf Of john rose
Sent: Friday, March 08, 2013 8:50 PM
To: arc5 mail list
Subject: Re: [ARC5] 10 meter BC-454 - screen voltage

Case in point that has had me scratching my head for years. I have a
R-392/URR, the compact, even svelte, lightweight (55 pounds or so) version
of the R-390/URR (not A). It is designed to run on 24 volt B+ and is loaded
with tubes designed to run at this level (26A6, 26C6, 26D6 etc). Every
characteristic chart I have ever seen, and I've done a lot of looking,
graphs out to 200 v or more. Will the tube really run at that B+? Are the 26
series really 6/12 v tubes with a different filament?

----------------------------------------
> From: brianclarke01 at optusnet.com.au
> To: kgordon2006 at frontier.com; Arc5 at mailman.qth.net
> Date: Sat, 9 Mar 2013 10:56:49 +1100
> Subject: Re: [ARC5] 10 meter BC-454 - screen voltage
>
> Hello Ken,
>
> The tube characteristics written in tube manuals (whose?) are for 
> establishing other characteristics, like life, gain and emission. They 
> are not set in stone.
>
> If you want a quiet receiver, I would leave the Voltage regulator 
> tubes out - they rely on ionisation of the enclosed gas = very noisy. 
> I know 'coz I tried it once - with a BC-454.
>
> If you want to experiment with tube element Voltages, set up an octal 
> socket on a breadboard, and measure noise and distortion vs Voltage. 
> Trying to do that inside a built receiver makes it very difficult to 
> discover what's causing what.
>
> 73 de Brian, VK2GCE.
>
> On Friday, March 08, 2013 8:14 AM, you said:
>
>
> > Looking at the tube tables, I see that the screen voltage to the 
> > 12SK7s is
> > 150 VDC when the
> > plate voltage is 250 VDC. When the plate voltage is 100 VDC, the 
> > screen voltage should also be 100 VDC, according to those tables.
> >
> > Both ratings are for when the tube is operated in Class A.
> >
> > This receiver is still using the original screen-voltage 
> > voltage-divider (the two black wire- wound resistors standing up in 
> > the back). Screen voltage is 75 VDC to all the tubes in the 
> > receiver, except the 12A6. Plate voltage, with the power supply I am 
> > presently using, is 275 VDC.
> >
> > I wish to reduce the plate voltage to no more than 180 VDC. I plan 
> > to use a VR-75 and a VR-
> > 105 in series for this.
> >
> > What is the consensus concerning screen voltage to the RF and IF amps?
> >
> > My plan is to raise it to at least 100 VDC via a resistive voltage 
> > divider across the 180 VDC regulated input.
> >
> > In your opinion, what might be the result, both pro and con?
> >
> > In my opinion, this will result in greater gain (due to the higher 
> > relative SG voltage) and lower noise (due to the reduced plate 
> > voltage) at the RF and IF amps.
> >
> > Ken W7EKB
>
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