[Amps] Grounded Grid (Screen) 4CX250B power gain

[DF3KV]

The Collins 30S1 is a good example were it is done with a 4CX250B style tube

73
Peter

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Carl
Sent: Dienstag, 21. Juli 2009 20:59
To: Colin Lamb; robert briggs; amps at contesting.com
Subject: Re: [Amps] Grounded Grid (Screen) 4CX250B power gain

I dont believe there is any way to run a 4CX250 style tube in GG without 
destruction. Very few tetrodes have the necessary grid dissipation required.

A relay driven bandswitching input network is one way to improve the THP 
circuit. Another is a regulated screen supply.

Using 4  4CX350's or 8930's should give an easy 1500W. Or water cooled 
8072's since the basic tube is dirt cheap.

Carl
KM1H


----- Original Message ----- 
From: "Colin Lamb" <k7fm at teleport.com>
To: "Carl" <km1h at jeremy.mv.com>; "robert briggs" <vk3zl at bigpond.com>; 
<amps at contesting.com>
Sent: Tuesday, July 21, 2009 1:37 PM
Subject: Re: [Amps] Grounded Grid (Screen) 4CX250B power gain


> "Tokyo High Power marketed a cathode driven 2 X 4X150/4CX250 amp that had 
> IMD
> on par with grid driven. The price was high for the power and didnt sell
> well in the US. The few I worked on were well built and looked acceptable 
> on
> the SA for IMD......on par with the exciters.
>
> http://bama.edebris.com/manuals/tokyohpl/hl1ka"
>
> I downloaded the manual and it has a nice schematic.  As Carl said, it is 
> cathode driven.  It is not grounded grid.  The screen voltage would be 
> about 380 volts (regulated only by a heavy bleeder resistor from a 
> capacitor only filtered power supply). The grid is bypassed to ground and 
> fed from an adjustable bias supply.  The cathode is fed through an 
> attenuator.  By operating the screen at normal voltage, the gain of the 
> tube will remain relatively high.
>
> Grounded grid configuration should have some improvement in imd over 
> grounded cathode because of the negative feedback inherent in that 
> circuit.  I have seen quotes of approximately 3-5 db or so.  Additionally,

> adding a tuned input would pick up a few additional db.  The measurement 
> of this improvement, however, would be difficult, because the tuned input 
> would improve the imd of the transmitter driving the amp (or, to be more 
> specific, the lack of a tuned input could decrease the imd of the 
> transmitter).
>
> All this is speculation without adequate tests and measurments to confirm 
> it.  I wish I had the time, energy and workspace to make such tests.
>
> 73,  Colin  K7FM
> 

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