[Amps] Re: one PS two RFdecks

[David Smith]

Ed,

I'm building the same only with three RF decks (2m, 70cm & 23cm).

Firstly, you should interlock the PTT lines so that only one can be keyed at
a time.  That way, you can have heaters/blowers on for all, ready for DX.

My amps are all grounded-grid.  The plate and grid current metering shunts
are both in the PSU.  I use 1 ohm for plate and 10 ohm for grid.  Each RF
deck has its own meters.  The meters are effectively 1 volt FSD voltmeters -
1mA 100 ohm meters with 900 ohm (2 x 1800 ohm resistors in parallel) in
series- indicating 0-1 amp for plate and 0-100 mA for grid.  You could
change the 900 ohm resistance if your amps draw different currents (e.g.
0-50mA grid current use 400 ohm series resistance).  The keying line also
disables the metering for the non-keyed RF decks, otherwise all the meters
will dance to the same tune (i.e. when all are unkeyed, all meters are
enabled).

By the way, make sure the meter shunts are ROBUST resistors.  If they go
open due to a flashover or similar, there'll be HV where it definitely
shouldn't with possibly dangerous results.  I use paralleled 2 x 22 ohm 25W
plus 1 x 100 ohm 10W for the grid shunt and similar for the plate shunt.
Also, a series string of 3 x 6A diodes both ways across the shunts to
hopefully bypass any HV glitches to ground.

And you've hopefully also got the glitch protection resistor in series with
the HV line (10 to 20 ohms per kV).

Regards,
David Smith
VK3HZ

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Date: Tue, 27 May 2003 12:53:32 +0000
From: Ed Stallman <n5blz1 at houston.rr.com>
To: amps at contesting.com
Subject: [Amps] one PS two RFdecks
Message-ID: <4.1.20030527114457.00962c30 at pop-server.houston.rr.com>

Here's what I'm trying to do, using one PS and two RF decks, I would like
to select the PA I want to use by turning on the heater and blower on  the
selected amp or both. no chance of driving both at the same time, use one
radio and each band has it's own keying circuit.. here's what I tryed, I
came out of the HV supply with the B- and B+ in parallel to both the 2m and
6 m pa... both PA's have there own heater voltage and metering circuit.
the results are the plate current meter on either amp works fine, but the
grid current meters almost double.
what do you all think? maybe I should use a relay or waffer swicth?
Thanks Ed N5BLZ