[Amps] cathode driven 4CX tubes.

[Fuqua, Bill L]

I was just looking at Bill Orr's article about super cathode driven tube amps in the July 67 QST.
He has a example of a 4CX300A (control grid connected to cathode) cathode driven amplifier.
It only has a power gain of 5. 375 watts out with 75 watts input. But the nice thing is that the 3rd order products were 46db down and
5th were -49. This is quite an improvement over most amplifiers. 
    I have always wanted to do this using two stages one produce around 300watts output and the second 1500 watts.
A 4CX250b driving 4 parallel 4CX250B tubes. Should get similar results.  This naturally would require 50 to 70 watts drive. 
________________________________________
From: amps-bounces at contesting.com [amps-bounces at contesting.com] On Behalf Of Fuqua, Bill L [wlfuqu00 at uky.edu]
Sent: Wednesday, October 13, 2010 12:53 AM
To: DF3KV; amps at contesting.com
Subject: Re: [Amps] 6146 via 572b's

I chose the 4cx250b tubes because they are readily available at hamfest and are reasonable, even new.

73
Bill wa4lav

________________________________________
From: amps-bounces at contesting.com [amps-bounces at contesting.com] On Behalf Of DF3KV [df3kv at t-online.de]
Sent: Tuesday, October 12, 2010 8:22 PM
To: amps at contesting.com
Subject: Re: [Amps] 6146 via 572b's

The 4CX350A is happy with 2 Watts through a 1:4 unun, if a 200 ohm grid
dummy load is used it does 350W.
When the grid is loaded with 50 Ohm 7W are sufficient for 350W out.

73
Peter

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Gary Schafer
Sent: Dienstag, 12. Oktober 2010 21:37
To: 'Bill Fuqua'; 'johne tds.net'; 'amps'
Subject: Re: [Amps] 6146 via 572b's

Passive grid 4CX250B requires around 25 watts drive. The 4CX250B requires
around 50 volts bias on the grid so it would take around 25 watts at 50 ohms
to reach that peak voltage. Passive grid with a 4:1 step up transformer may
do the job.

73
Gary  K4FMX

> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Bill Fuqua
> Sent: Tuesday, October 12, 2010 2:02 PM
> To: johne tds.net; amps
> Subject: Re: [Amps] 6146 via 572b's
>
>     My choice for a tube 5 w to 500+ watt amplifier would be a
> pair of 4CX250B's with a passive grid class AB1.
>     Grounded grid would be out of the question unless you plan to have
> two stages of amplification.
> 73
> Bill wa4lav
>
>
> At 02:15 PM 10/12/2010 -0400, johne tds.net wrote:
> >I was in qso with a another ham about a tube type amp that could be
> >used with our  Yaesu FT-817 's. The FT-817 will do about 5 watt's on a
> >good day.  He recalled that he did know of a amp like this.  So
> >looking for a name or a schematic ?
> >
> >Thanks de John K0CQW
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