[ARC5] 10 meter BC-454 - yet more

[Geoff]

There is a difference between remote cutoff and extended cutoff that some 
manufacturers referred to as semi remote. In a simple radio without multiple 
AGC loops it was prone to easily overload.

The 6AC7 had an almost zero use as a gain controlled RF amp in any 
commercial products that I am aware of and was often used as an AVC, S 
Meter, panadaptor IF amp, or similar application.

Another problem as an RF amp is that the grid circuit loaded the input 
coils, broadened the bandpass, and reduced image rejection in low IF sets. 
Not a problem on the high IF ARC-5's with images.




----- Original Message ----- 
From: "Ian Wilson" <ianmwilson73 at gmail.com>
To: "ARC-5 List" <arc5 at mailman.qth.net>
Sent: Tuesday, February 05, 2013 1:41 AM
Subject: Re: [ARC5] 10 meter BC-454 - yet more


> The 6AC7, according to the data sheet, is either sharp cutoff or remote
> cutoff depending on how you control the screen grid:
>
> *When a fixed screen voltage is used, as shown in condition 1, a
> sharp-cutoff*
> *characteristic is obtained.*
> *
> *
> *When a screen resistor is used, as shown in condition 2, an extended 
> cutoff
> *
> *characteristic is obtained which may be utilized in applications where 
> the*
> *gain is controlled by variation of the grid bias.*
>
> (GE data sheet).
> Condition 1: 150v fixed screen voltage.
> Condition 2: 60k screen resistor to +300v.
>
> 73, ian K3IMW
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