[Amps] Triode Amps

[jim.thom jim.thom@telus.net]

Date: Fri, 3 Dec 2021 18:23:28 -0600
From: Kim Elmore <cw_de_n5op at sbcglobal.net>
To: amps at contesting.com
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 ma...like 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