Carl wrote:
> Yes, if you mean cathode driven. It has less grid dissipation than a 250.
>
>
Yah can't get much less than zero<:-))
73
Roger (K8RI)
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "DF3KV" <df3kv@t-online.de>
> To: <amps@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@contesting.com [mailto:amps-bounces@contesting.com] On
>> Behalf Of Carl
>> Sent: Dienstag, 21. Juli 2009 20:59
>> To: Colin Lamb; robert briggs; amps@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@teleport.com>
>> To: "Carl" <km1h@jeremy.mv.com>; "robert briggs" <vk3zl@bigpond.com>;
>> <amps@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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