Ive no idea if any date code could be considered good or bad John.
My only experience with them was in a couple of HT-33's that were in for
service decades ago and then I was told the reason for premature failures by
a few of the VHF amp builders..
The USAF was a large user and they regularly surplused off stock after so
many years so they didnt get caught with a problem. If you notice, NOS
300's are everywhere.
Geralds idea is a good one that can be built also with PS components on hand
for the proposed project.
Carl
KM1H
----- Original Message -----
From: "John Finner" <finnerjf@worldnet.att.net>
To: <amps@contesting.com>
Sent: Friday, January 15, 2010 9:08 PM
Subject: [Amps] 4CX300a Seal Leaks
>I read a post by Carl, KM1H on August 10, 2009 that read:
>
> There are several ceramic tubes that are notorious for seal leakage. The
> 4CX300A is a classic.
>
> This post is directed to Carl. The list might also be interested. I would
> be interested in a brief explanation of the problem.
>
> I have 7 NOS JAN 4CX300A's an am building a 3 tube passive grid driven
> amp. The date codes are 7204, 7432 and 7634 if this makes a difference.
> Are the JAN Eimac tubes less problematic?
>
> The amp is in a simibreadboard state with 4CX250B's. Since I now have 3
> sockets for the 4CX300A's, I will switch tubes and raise the Ep to 2500 V.
> I do not want to waste my time if I am going to have a problem with this
> change.
>
> John WA4EPI
>
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