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Re: [Amps] 3-500Z cool down time

To: "Charlie Young" <>, "Joe" <>, "Catherine James" <>, "Amps group" <>, "Kimberly Elmore" <>
Subject: Re: [Amps] 3-500Z cool down time
From: "Carl" <>
Date: Tue, 6 Jun 2017 13:25:43 -0400
List-post: <>
I suspect that Eimac put a lot more effort into conditioning the tubes back then. Pull a better vacuum and the breakdown voltage increases.

Ive hi-potted some beyond the 13KV capacity of my tester. OTOH youre lucky to get 8KV out of Chinese versions.


----- Original Message ----- From: "Charlie Young" <> To: "Joe" <>; "Catherine James" <>; "Amps group" <>; "Kimberly Elmore" <>
Sent: Tuesday, June 06, 2017 11:36 AM
Subject: Re: [Amps] 3-500Z cool down time

I have seen some 3-500 tubes affected by long storage and some not.

In 1995 I bought a new matched pair of Eimac 3-500 tubes. The date code on the tubes is 1994. Once in the early 2000’s I tested these tubes and they were OK. Pulled them out and placed them back in storage; I was not running an amp that used them. Fast forward to about 2011 and they were both gassy when put into an AL-82. Arc city. I don’t know if they can be rehabilitated or not by bringing up the HV low and slow and biasing them to conduction so the plates heat up. I have not tried that yet, but plan to do so soon.

On the other hand, I bought an old SB-220 from a CB operator back in the early 1990’s. The Eimac tubes in it have 1973 date codes. This amp was never fired up from 1996 until it was converted to 6 meters in 2010. These tubes are fine, and still make 1400W on 6 meters. No arcing at all even when first fired up.

So, I think it depends on the individual tube.

73 Charlie N8RR

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From: Joe<>
Sent: Tuesday, June 6, 2017 11:21 AM
To: Catherine James<>; Amps group<>; Kimberly Elmore<>
Subject: Re: [Amps] 3-500Z cool down time

So this SB-220, that has been sitting since 1993, the tubes are most
likely toast?

The Original Rolling Ball Clock
Idle Tyme
On 6/6/2017 10:14 AM, Catherine James wrote:

It's generally recognized that glass tubes have poor shelf life due to slow leakage. I have heard many reports of this from people I trust.

They will last much longer if the plate gets hot at least a few times a year so that any leakage can be gettered away. For tubes in regular use rather than on the shelf, it doesn't seem to be a problem, but it makes it difficult to stock up with spares. Many amateur users rotate their shelf stock into the amp at least once a year.

Is the 3-500Z used much outside of ham radio today? If so, who are the primary users?


On Tue, 6/6/17, Kimberly Elmore <> wrote:

  The biggest issue with the 3CX1200 is appears to be that
  it's simply not used in much outiside of ham radio.
  I'm not sure what the original design application was
  intended for, but I'm pretty sure it wasn't just for
  amateur use.

  As for glass tubes, I know that some are notorious for leaky seals,
but I thought such was rare. Is it a significant problem with the 3-500Z?

         From: Catherine James
   To: Amps group
   Sent: Tuesday, June 6,
  2017 9:04 AM
   Subject: Re: [Amps]
  3-500Z cool down time

  that ceramic tubes appear to last longer on the shelf with
  less leakage than glass, it's a shame that there
  isn't a ceramic tube in the price/performance range of
  the 3-500Z.  It would be well worth paying, say, 10% more
  for ceramic.  But the actual cost multiplier is much higher
  than that, so glass tubes will continue to rule at the low
  end (i.e., far below legal limit).

  Kimberly Elmore <>

  enough; I was simply

  statingthat the 3CX1200 is a ceramic replacement for a
  It's a fine tube, though it requires a fair
   bit more drive. That is,
  aparently, the price paid for a
   high grid dissipation rating. It's easier to
  drive when
   running 4
  kV B+, though. At that voltage, I never fail to
   acieve full output with a
  100 W rig on any band.
   Kim N5OP

     From: Bill Turner
    To: Amps group <>

    Sent: Monday, June 5,
  2017 9:32 PM

  Subject: Re: [Amps] 3-500Z cool down time

   ------------ ORIGINAL
   MESSAGE ------------(may
  be snipped)

   On Mon, 5 Jun 2017
  20:48:40 -0500, Kim


   >The 3CX1200 is a
   ceramic version of the
  3-1000Z. I have an amp that uses one
   and it's ready in
  under 10 s.



   Yes, but that's a
   expensive tube. I
  was thinking of a ceramic
   3-500Z for the same price as glass.

   For what they are asking
   might as well get
  an 8877. Different

   but lower drive
  and more output.

   73, Bill W6WRT

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