Glenn McNeil wrote:
>Hi Guys,
>
>I'm about to begin the last phase of my 144 / 432 Mhz GS35B Amp
>Project...that is, building a common Power Supply to run both Amps. I'm
>intending to use Ian, G3SEK's Triode Protection Boards....one in each
>Amp. The Power Supply has a 240/2300 vac at 1A Transformer ( 400w PEP
>Max Power in VK ), a 40uf 5kv Oil Filled Cap, Bridge Rectifier with big
>meaty diodes in each leg and Step Start.
>
>As Ian's System uses an HV Enable line, I propose to operate both Amps
>at the same time, but never both keyed at once... i.e HV will be on both
>Amps at the same time, but each Amp has its own individual Filament and
>Bias Supplies.....and run each HV Enable Line to one of those Russian
>Vacuum Relays that are listed on eBay for a reasonable price. So,
>instead of switching the EHT Transformer primary off if a fault
>condition develops, I'll drop off the EHT via the Relay to the faulty
>Amp.I will have a common glitch resisitor in the Power Supply, before
>the Vac Relays. I use a common Station Sequencer that only enables me to
>key up one band at a time.
>
>The primary reason for this line of design is to save a few bucks, and
>more importantly, some room ! I also have future plans, if this initial
>system is a success, of expanding the whole thing to run HF and 50 Mhz
>as well, using the same type of tubes and the same supply...4 Amps off
>of one common EHT Supply.
>
>Can anyone see any impending trouble with this type of design, or any
>reason why you cannot run the G3SEK System in multiple Amps, all using
>the one EHT Supply...with the return - HV line from each Amps G3SEK
>board all tied in a knot at the -HV point in the EHT Supply ? I've been
>staring at the circuits for a few hours trying to see if there are any
>traps for young ( and not so young ) players here..in relation to
>parallel current paths that may upset things. Looking back out of the
>common -HV point in the Power Supply, I will have initially two sets of
>Anode and Grid Meters essentially in parallel with each other, but only
>ever one set doing anything at any given time. I don't think I can see a
>problem, but other, wiser heads may know otherwise.
Yes, it can be done. To keep the two sets of grid and anode current
meter from interacting, each board needs a large diode in the HV-minus
connection (another GI750) with the cathodes commoned to the negative
rail of the HV supply.
Also you don't need relays in the HV+. The kinds of faults that cause an
HV trip are quite rare, so it's normally OK that an HV trip in either
amp should switch off the whole HV supply to both amps. A
single-operator station can always accept that limitation. (If anything
has caused an anode-current surge that was big enough to trip one of the
amps, I would definitely want that HV power supply to switch off
completely while I investigate.)
It's quite easy to make a 'voting' system that won't energize the HV
mains contactor unless both HV_ENABLE lines are up, and will make it
drop out if either one of those lines goes down. One +12/24V DC
HV_ENABLE line is wired to the hot end of the mains contactor coil in
the normal way. Instead of the cold end of the coil being directly
grounded , it connects to ground through an NPN transistor that is
switched on by the HV_ENABLE line from the other amp (through a 1k
series resistor to the base). If either line goes down, the contactor
drops out. To use only one amp at a time, you'd need a manual over-ride
switch, but it's all simple low-voltage circuitry. The whole thing would
be much less trouble and expense than HV relays, and better in many
ways.
--
73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
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