Hi Alan,
Here is my solution to that:
http://qsl.net/wc6w/wc6wamps/index.html?fr63.html
73 & Good morning,
Marv WC6W
http://qsl.net/wc6w/
--------------------------------------------
On Sun, 4/24/16, Alan Ibbetson <alan@g3xaq.net> wrote:
Subject: [Amps] 8877 heater inrush
To: amps@contesting.com
Date: Sunday, April 24, 2016, 8:01 AM
I am collecting parts together to
build a rugged but low weight
amplifier for solo DXpeditions. I have an 8877 tube that I
want to use.
A 5V switchmode PSU instead of a mains transformer for the
heater looks
a good way to keep the weight down but the low resistance of
the cold
heater (0.05 ohms for the tube I have to hand) means I will
need to
limit the current on switch on, not only to babysit the
valve but also
to prevent the SMPS going into foldback or hiccup limiting.
I can envisage a number of approaches to providing the
required step
start based on relays or solid state switches but they
require an
estimate of the time it takes for the heater element to
become hot
enough at reduced voltage to offer a "reasonable" resistance
for when
the full heater voltage is applied.
Does anyone have data on the heater startup current on an
8877? Curves
of both steady state current versus voltage and of current
versus time
at fixed voltage would be useful. Please note that I am not
asking about
the time it takes for the cathode to reach operating
temperature; that
is well documented.
73, Alan G3XAQ
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