[Amps] Quad Tube 4cx800 hf amp

[Leigh S. Jones, KR6X]

http://www.tomstubes.com/4CX800A.htm for a data sheet

You've got some problems.  First of all, the tube is good for 2 KV DC and 
pushing it to 2.6 KV would not be recommended.  Secondly, the output 
capacitance is not nearly as high as you imagine (9-13 pf).  Your design 
needs to be for a lower plate impedence if you stick to the 4 tube formula. 
2.0 KV at 3.0 A peak.  If you need to push it, you could use a Pi network 
output circuit in lieu of a Pi-L network to raise the C1 capacitance on 10 
meters.  Then you would use a high quality low pass filter to reduce the 
harmonics.  Frankly, I don't think you should need to do that; the 4CX800 
should be easy to run on 10 meters in pairs or quads.  But I recommend the 
pair.

----- Original Message ----- 
From: "Manuel R. Alonso / KC4MNE" <kc4mne at bellsouth.net>
To: <amps at contesting.com>
Sent: Thursday, May 25, 2006 6:50 PM
Subject: [Amps] Quad Tube 4cx800 hf amp


> Hello
>
> Would it be feasable to build a 4  tube amplifier using the 4cx800 russian 
> tubes.
>
> I calculated a plate impeadance of about 490 ohms, using (2600V 3.0 amp 
> supply)
>
> However for a Pi output I am looking at a c1 value of about 100 pf at 
> 29MHZ and each tube has 51pf of capacitance already, if added together 
> thats over 200pf.  How is this obstacle corrected?
>
> Manny
>
> KC4MNE
>
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