[ARC5] 10 meter BC-454 - yet more

[Geoff]

There is nothing new about that as almost all RF and IF amps used at least 
one screen dropper of 22-56K going back to the 30's.  As AVC circuits 
advanced it was used on all stagesa nd right to the end in the 70's.

The 6BA6 can trace its lineage back thru the 6SK7, 6K7, 6D6, and 78, plus 
the 44 and 35 tetrodes.

Carl



>  Just looked at GE's data sheet on the 6BA6 and guess what.
> They show an optional 33k screen resistor instead of fixed voltage to 
> extend the cut-off voltage even more negative.
> It is a remote cut off already, this suggest that this technique may be 
> used for later stages to
> reduce clipping and allow larger plate voltage swing.
> 73
> Bill wa4lav
>
>
> At 09:49 AM 2/5/2013 -0500, Geoff wrote:
>>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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