[Johnson] Re: Invader 2000

[Mahlon Haunschild]

SCott, I'm not surprised that the bias voltage is the only change in the 
Invader 2000, but I would be surprised if the tube swap was the only 
circuit change.  Also, I believe you've got your bias voltaged flipped. 
  I have both Thunderbolt manuals, and I own a 4-400A Thunderbolt plus a 
PL-175A Thunderbolt carcass.  I'm not familiar with the Invader 2000, so 
all I can speak to is what's in the Thunderbolt:

In a PL-175A thunderbolt, the regulator tube is a VR90 and the dropping 
resistor is 5.6K 2 watt.

In a 4-400A Thunderbolt, the regulator tube is a VR75 and the dropping 
resistor is 2K 10 watt.

So, unless the transformer voltage changed, you may need to change the 
dropping resistor too.

regards,

Mahlon - K4OQ

> --__--__--
> 
> Message: 7
> From: "Scott Prather" <n7nb@worldnet.att.net>
> To: "Kenneth" <w7itc@msn.com>,
> 	"George Shapow" <gshapow@rochester.rr.com>,
> 	<johnson@mailman.qth.net>, "Roy Morgan" <roy.morgan@nist.gov>,
> 	"Ed Wirtz" <ewirtz@hbci.com>
> Subject: RE: [Johnson] Invader 2000
> Date: Tue, 27 Apr 2004 18:38:26 -0700
> 
> I studied this aspect of the Invader 2000 quite closely at one time, and it
> appears that the only modification necessary to use 4-400's in place of the
> PL-175's is a change to the bias voltage.  In the Invader (and the later
> Thunderbolt that used PL-175s) the bias voltage is -75, provided by an 0C2
> regulator tube in the case of the Invader.  In the earlier Thunderbolt that
> used 4-400's, the bias voltage is -90.  The Invader uses an 0C2, which is a
> 7-pin miniature tube, while the Thunderbolt with 4-400's uses the octal
> VR-90. I don't know of a 90 volt regulator tube in a 7-pin miniature, so in
> my Invader I simply cut the lead that grounds the plate of the 0C2 and
> inserted a 15 volt, 1 Watt zener.  This provided the requisite -90 V,
> assuming the OC2 is still good (my original 0C2 was regulating to a mere 68
> volts).
> 
> Hope that this helps.
> 
> Scott
> N7NB