[Johnson] Invader 2000

[email protected] [email protected]
Tue, 27 Apr 2004 9:05:57 -0400


George,

The 4-400A and the PL-175A are NOT the same tube, though they look similar.  In class AB1 / AB2 service different grid bias voltage is required for the two tubes.

You might want to consult the two Thunderbolt manuals on BAMA.  I think that the Invader 2000 and Thunderbolt uses essentially the same amplifier and HV power supply; the two versions of the Thunderbolt manual will show you what circuit  changes are made when going from a 4-400A to a PL-175.

The changeover may be very easy to do:  change the grid bias regulator tube & series resistor.  That's all it is for the Thunderbolt, but there may be more to the changeover in the Invader 2000.

GL.  regards,

Mahlon - K4OQ
> --__--__--
> 
> Message: 1
> From: "George Shapow" <[email protected]>
> To: <[email protected]>
> Date: Mon, 26 Apr 2004 09:39:45 -0400
> Subject: [Johnson] Invader 2000
> 
> Hi all,
> 
> I have an Invader 2000 in need of finals.  It uses PL-175As but I've been
> told that 4-400s are direct substitutes.  Is that true?  Also, Does anyone
> know where I can get them at a reasonable price?
> 
> Thanks
> 
> George, NY2O