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Re: [Amps] SB220 running plate current when no drive; Problem

To: David Gow <>
Subject: Re: [Amps] SB220 running plate current when no drive; Problem
From: Kim Elmore <>
Date: Thu, 8 Oct 2020 10:51:41 -0500
List-post: <>
I had an AL80A for which I built a 4000 V power supply. The output network 
needed a fair bit of change on the low bands because the load point changed, 
but it would easily make 1200 W out on 40 m (the sweet spot for that amp). It 
was much easier to drive, too. I also replaced the original fan with a quieter, 
highe-volume flow one

The manual states not to exceed 200 mA grid current; Eimac instead provides max 
grid dissipation numbers and maximum tube seal temperatures, along with a max 
anode current of 400 mA. I figured that as long as the tube seals stayed in 
spec, the rest took care of itself. 

I re-wrote the tune up procedure in the manual then sold that amp to a guy that 
really wanted it warning him that if he didn’t pay strict attention as he tuned 
it he was at risk of causing the band switch to arc. I assume he’s still using 
it as I never heard of any trouble from him. 

Kim N5OP

"People that make music together cannot be enemies, at least as long as the 
music lasts." -- Paul Hindemith

> On Oct 8, 2020, at 10:38 AM, David Gow <> wrote:
> For actual Eimac tubes the Eima DATA sheet shows much greater
> efficiency and usable power with 4000 volts on the plates.  Henry made
> several amps with a 3200 or 4000- volt switch and  the 3KA   I had easily
> made the legal limit  at 4000 volts with the original tubes after 21 years
> withHenry spec. grid and plate current being carefully maintained.  He
> wanted to buy new tubes and I discouraged him,  When I last heard from him
> four years after the sale he was still running the Eimacs. with a new pair
> of chinese tubes on the shelf gathering dust losing vacuum.
> Dave W7VM
>> On Thu, Oct 8, 2020 at 6:27 AM Joe <> wrote:
>> What is the current (pun intended) max grid current for a pair of
>> 3-500Z's now days?
>> And does it matter what the Plate voltage is?
>> Joe WB9SBD
>>> On 10/8/2020 6:39 AM, Rob Atkinson wrote:
>>> Never heard of an ICAS rating for the 3-500.  I have a dual 3-500
>>> amplifier with a pair of 20 year old RF Parts 3-500s and they're still
>>> at full output, but they have been run conservatively especially with
>>> regard to grid current.
>>> 73
>>> Rob
>>> K5UJ
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