[Johnson] Invader 200

[jeremy-ca]

I cant say if the change was real but the effect would be to reduce the 
plate dissipation of the 12BY7 quite a bit and therefore prolonging its 
life.

The 12BY7 was used in many products including Japanese and short life is a 
problem with several.

Now, does the reduced output provide enough drive?

Ideally the screen voltage would be adjustable allowing optimum drive and 
long life.

Carl
KM1H




----- Original Message ----- 
From: "David C. Hallam" <dhallam at rapidsys.com>
To: "Johnson List" <Johnson at mailman.qth.net>
Sent: Monday, April 28, 2008 2:36 PM
Subject: [Johnson] Invader 200


>I am in the process of refurbishing another Invader 200 and have picked up
> something on the schematic. R65, which is the screen resistor on the 
> 12BY7A
> driver, is 10K ohm.  The latest version that I have of the parts list also
> lists it as a 10K resistor and on the schematic dated 1/9/61 it is shown 
> as
> a 10K.  However, on schematics dated 2/18/63 and 11/15/64 it is shown as
> 18K.
>
> In the Johnson correspondence I have I can find nothing about a change of
> this resistor from 10K to 18K.
>
> Does anyone know whether this is an error that has crept into the 
> schematic
> or is it an undocumented change?
>
> There is an error on the 11/15/64 schematic in that R25, a 47 ohm resistor
> in the keying line, was left off.
>
> David
> KC2JD/4
>
>
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