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Re: [Amps] Triode Amps

To: "jim.thom" <>
Subject: Re: [Amps] Triode Amps
From: Kim Elmore <>
Date: Sun, 5 Dec 2021 21:47:44 -0600
List-post: <>
My guess is that the hardware to withstand higher B+ Is hard to come by. That 
and anything beyond 4 kV goes off the charts, so no one can say for sure what 
the characteristics are when run beyond 4 kV so it becomes an experiment that 
most aren’t truly ready to carry out. 

Kim N5OP

> On Dec 5, 2021, at 11:23 AM, jim.thom <> 
> wrote:
> Date: Fri, 3 Dec 2021 18:23:28 -0600
> From: Kim Elmore <>
> To:
> Subject: Re: [Amps] Triode Amps
> <I should have qualified my response: 1500 W is indeed possible out of a
> <pair of 3-500Zs, but the cooling must be letter perfect: air sockets,
> <proper chimneys and proper plenum pressure. I suppose you could get 2+
> <kW out of a pair of you ran them at a much higher B+ (well over the 4 kV
> <max defined by Eimac), higher I_p and at the grid dissipation limit,
> <i.e., and well out of their limits, but they won't last very long that
> <before they fail. If cooling is sufficient, I suspect you could run 1.5
> <kW output for RTTY and FT8 (essentially CCS), but there probably won't
> <be much head room.
> <Kim N5OP
> ##  Agreed.  Elevated  B+ is a non issue.  The tubes will hi-pot test  to
> 15 kv. To get 4 kv  loaded, would require 4.4 kv  un-loaded.  Been there,
> done that.
> The cooling is straightforward.  Use chimneys that have the taper at the
> top..and use anode connectors  with vertical fins.  And the correct
> blower.  The  EBM papst blower from the AL-82 /  AL-1500 /  AL-1200  works
> fine.  Loads of other blowers that will provide even more airflow.
> Use the correct amount of bias.  100 ma of idle current  is ample for a
> pair of tubes..and  2600 vdc.   And even less idle current  when  higher B+
> used.  IMD is superb.  40 ma of idle for a pair, when1900 vdc used still
> results in good  imd.
> On  CW, idle current can be reduced  to just above zero 10-20
> ma.  You can't reduce the idle to zero on  CW, or u will then get key
> clix.   Same deal with data modes, idle current can be reduce to just
> 10-20 ma.
> Ideally, a  3 x   3-500Z amp, or even 4  tubes would be optimum, and leave
> some wiggle room.
> For data modes,  I would not run the existing amps at >  1 kw.   When
> switching from  SSB  to data modes, the average plate current doubles....
> and watts dissipated in the tank coils and band switch quadruples.  1.5 KW
> on data modes is a bunch.  It's not just the tubes you have to worry about,
> it's everything else, like tank coils, padders, bandswitch, HV xfmr, etc,
> etc.
> Jim   VE7RF
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