[Amps] NCL-2000 retube

[Fuqua, William L.]

OK,
The 4CX300Y and the 4CX350A have the same size anode heatsink and similar fin area.
The 4CX300A has about half the fin area. The 4CX300 tubes bases are about half the diameter of the
4CX350A, 4CX250B or 7034 tubes. This offers less restriction to air flow thru the socket to the anode
heat sink.
  Even tough the 4CX300Y specs indicate max plate voltage of 2000 VDC they should be just fine at 2500 VDC.
The screen voltage of 400 VDC is fine, but the grid bias needs to be -70 to -75 or so.
You will have to increase R40 to get it in the same range.
  At 2kW PEP plate input the amplifier is really pushing the 8122's fairly hard into class AB2.
I would recommend with the replacement tubes you stay in AB1 keep the splatter to a minimum.
Just a small flicker of the grid current on occasional voice peaks.
  EIMAC made 8122s as well, but the data sheet did not include AB2 operation, just AB1 for SSB suppressed carrier service.
  The 4CX300Y tubes are readily available on E#(*$ for $69 plus shipping and you can shop around for sockets and chimneys.
Chimneys are the same as for 4x150, 4cx250B, etc..
  73
Bill wa4lav
________________________________
From: Amps <amps-bounces at contesting.com> on behalf of Fuqua, William L. <wlfuqu00 at uky.edu>
Sent: Friday, August 19, 2022 12:45 AM
To: Paul Decker <kg7hf at comcast.net>; Radio WC6W <wc6w_amps at yahoo.com>
Cc: amps at contesting.com <amps at contesting.com>
Subject: Re: [Amps] NCL-2000 retube

CAUTION: External Sender


   A pair of 4CX300Y tubes. Yes, they do use special sockets, but both tubes ($60 ea. new in can) and Sockets are readily available
on E$(#*. The have 400W plate dissipation. Bias changes will have to be made. The base is skinner than the the 4CX250B or the 4CX350A
thus allowing better air flow to the anode. The 4CX300A would work just as well. The 8122 plate dissipation was a bit overrated, however.
They were intended as a cheap alternative for the 4CX250B or 4X150A/7034.
  73
  Bill WA4LAV

________________________________
From: Amps <amps-bounces at contesting.com> on behalf of Paul Decker <kg7hf at comcast.net>
Sent: Thursday, August 18, 2022 6:48 PM
To: Radio WC6W <wc6w_amps at yahoo.com>
Cc: amps at contesting.com <amps at contesting.com>
Subject: Re: [Amps] NCL-2000 retube

CAUTION: External Sender


_______________________________________________
Amps mailing list
Amps at contesting.com
https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.contesting.com%2Fmailman%2Flistinfo%2Famps&data=05%7C01%7Cwlfuqu00%40uky.edu%7C60cdc0405ade444f755008da819dafb8%7C2b30530b69b64457b818481cb53d42ae%7C0%7C0%7C637964811496035509%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=me2hEuuH0%2B8WjNCQiEINou7BziwEes7i6WXNvwb4s5E%3D&reserved=0
_______________________________________________
Amps mailing list
Amps at contesting.com
https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.contesting.com%2Fmailman%2Flistinfo%2Famps&data=05%7C01%7Cwlfuqu00%40uky.edu%7C60cdc0405ade444f755008da819dafb8%7C2b30530b69b64457b818481cb53d42ae%7C0%7C0%7C637964811496035509%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=me2hEuuH0%2B8WjNCQiEINou7BziwEes7i6WXNvwb4s5E%3D&reserved=0