The newer socket for the 4CX3500A, 4CX7500A newer tubes is not interchangeable
with the SK-300 or SK-300A...the height of the screen grid collect is different
in relationship to the control grid.
Terry - W6RU
John Lyles wrote:
> Hi,
>
> This is a slight aside from the HF socket application, but:
>
> In 1983, I worked with the Eimac engineers, while at Broadcast Electronics,
> Inc, on an improvement in the SK300A series sockets, for the 4CX5000A or
> the 4CX3500A. I cannot be sure of this part number right now, but they
> created the SK350/355 series I think, based on our design.There is a
> similar socket for the 4CX20,000A/8990 tetrode, and the intermediate
> 4CX7500A and 4CX12,000A tetrodes. Since we were using them at 100 Mhz, the
> SK300A was totally inadequate due to the open spaces and the high
> inductance, esp in the filament and screen bypassing. It was not DC
> grounded screen, but RF grounded (well, through straps for
> self-neutralization at 100 Mhz and plates insulated with Kapton film for
> bypass caps). The newer sockets had a series of holes for airflow, which we
> determined were not too detrimental for VHF operation - nothing like the
> big open areas in the 300A. The filament connections were bypassed with
> integral Pyralux (copper laminated Kapton polyimide film) capacitors
> sandwiched between the layers. Additional doorknobs (57 series) could be
> added for lower frequency bypassing.
>
> Pyralux and Kapton are E. I. Dupont de Nemours trademarks
>
> 73
> John
> K5PRO
>
To: <amps@contesting.com>
> >Date: Sat, 5 Dec 1998 13:13:02 -0800
> >From: Rich Measures <measures@vc.net>
> >Subject: Re: [AMPS] FS: 4CX5000A, socket, fil trans
> >
> >>SK300 socket includes screen bypass caps.
> >>
> >I bought such a socket at a surplus store. This socket is for audio
> >amplifier service, not RF service. In order to convert the AF socket for
> >RF use, I purchased the required parts from Eimac and removed the
> >doorknob caps. For stable RF amplifier service, the screen collet must
> >be grounded in eight places with c.10mm Cu ribbon. A diag. of the
> >grounded screen, grid driven configuration is on my Web site. While I
> >had the SK300 socket disassembled, I used a fine tooth coping saw to trim
> >excess metal from the screen and grid collets - thereby reducing back
> >pressure to cooling air, like an SK300A socket.
> >
> >- - later, Jack
> >
> >Rich. Measures.,www.vcnet.com/measures, 805.386.3734
>
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