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Re: [Amps] Supply question

To: "Sam Carpenter" <>, "'Rob Atkinson'" <>, <>
Subject: Re: [Amps] Supply question
From: "Carl" <>
Date: Wed, 20 Jul 2011 11:58:32 -0400
List-post: <">>
----- Original Message ----- 
From: "Sam Carpenter" <>
To: "'Rob Atkinson'" <>; <>
Sent: Wednesday, July 20, 2011 11:41 AM
Subject: Re: [Amps] Supply question

> When you run the 3-500 easy, you will have a greater chance of arcs than 
> if
> you run the cherry red or orange. The gettering material is on the anode 
> and
> it requires color, sometimes significant color, to eat up the full range 
> of
> gas. I would venture to say that you may have less chance of arcing in a
> higher voltage amp that is used regularly.
> -----Original Message-----
> From: [] On
> Behalf Of Rob Atkinson
> Sent: Wednesday, July 20, 2011 11:16 AM
> To:
> Subject: Re: [Amps] Supply question
> I understand that with 3-500 the 3rd order IMD gets pretty lousy when
> the Ep gets up there much above 3 KV.

Read the spec sheet.

> I also had some idea you get a much bigger chance of arcs in the tube
> if you push the Ep way up there near the limit.

Very true when gas is involved as the voltage needed to ignite is in inverse 
proportion. A 4000V amp still outgasses when not regularly used and is more 
prone to arc when turned on.

OTOH Chinese tubes may not even hi-pot at 7000V which is why Ameritron 
rejects so many since they could arc on a normal voice peak. I believe they 
test to 9 or 10KV. Even a little bit of gas will ignite an arc when the 
threshold is low.
A good Eimac used to hi pot above 12KV when new since they were rated for 
Class C AM at 3KV.

Personally I would never run any unknown tube without a hi pot first and if 
necessary a full gettering at around 1000V


> comments?
> 73
> Rob
> K5UJ
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