[ARC5] 10 meter BC-454 - screen voltage

[Geoff]

Too much gain and minimal gain distribution along with a primitive AGC, wide 
IF passband,  is a formula for overload in a real world open band 
enviroment.

Gain already appears more than enough to drive a speaker so why add more?

Minimize the noise and enjoy.

Carl


----- Original Message ----- 
From: "Dennis Monticelli" <dennis.monticelli at gmail.com>
To: "Ken Gordon" <kgordon2006 at frontier.com>
Cc: <Arc5 at mailman.qth.net>
Sent: Thursday, March 07, 2013 8:50 PM
Subject: Re: [ARC5] 10 meter BC-454 - screen voltage


> Ken,
>
> I think raising the screen voltage is a good idea because it will raise
> gain and that may improve the S/N ratio.  Lowering the plate will reduce
> dissipation and perhaps noise as well.  Your swing will be more limited 
> but
> only the 12A6 is going to see a big swing anyway.  I'd say, go for it.
>
> Dennis AE6C
>
> On Thu, Mar 7, 2013 at 1:14 PM, Kenneth G. Gordon
> <kgordon2006 at frontier.com>wrote:
>
>> 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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