related general warning to all...
increasing use of higher supply voltages on PAs these days,
28V and upwards, be careful what you feed small voltage
regulators with, especially those for bias and control
circuitry. Many low power low voltage regulators have a
maximum input voltage rating that may be a fair bit lower than
popular 78L05 and 78L033 devices, for example, are only
specified for 30V max on the input, so in practice you
shouldn't really be using them direct from even a 24V supply
to allow some safety overhead. And certainly not from a 28V
rail. And as for use on a 50V supply, there are only a few
voltage regulators around rated 60V input and higher. They do
exist, but need searching-out
adjustable LM317 family, including the L version, is a lot
better in this respect, allowing 40V ACROSS it. So this
makes for a low cost solution for a two stage regulator; use
an LM317 to drop 50V to, say, 18 - 20V, then your favourite
fixed voltage reg to go from 20V down.
thought I'd mention it, as there seems to be quite a bit of
construction of PAs and related stuff going on at the moment.
On Sun, 26 Apr 2020 at 11:13,
Andy GD1MIP <gd1mip@...
2E0IJH - Thanks.
John G4TZR - Thanks, I fully understand that Bert is busy and
as I am not the original customer I again understand that his
priority is to his business, himself and his paying customers.
So I have no complaint whatsoever in the speed of his response
or lack of. My reason for mentioning that I have emailed him
is because, in my experience whenever someone posts on a forum
asking a Bert question, people always reply saying... email
Thanks for commenting re the BIAS range, that puts my mind
at rest, I will now just use 28v rather than finding ways to
Again thanks re the monitor volts, I assumed each unit was
different so you'd get different readings on each amp
produced, however my limited knowledge meant it was best to
ask here for confirmation or is that comfort?
Testing so far has been on 28v for the PA and both 12 &
28v for BIAS, no difference noted. The unit runs remarkably
cool, event before I have fitted fans I already know they
will be needed only infrequently it isn't going to do much
unless I try data.
Thanks Andy GD1MIP