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

[Carl]

Yes, if you mean cathode driven. It has less grid dissipation than a 250.

Carl
KM1H


----- Original Message ----- 
From: "DF3KV" <df3kv at t-online.de>
To: <amps at contesting.com>
Sent: Tuesday, July 21, 2009 3:12 PM
Subject: Re: [Amps] Grounded Grid (Screen) 4CX250B power gain


> 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
>>
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps