## agreed about mixing triodes and tetrode amps. But IF its just 2+ GG
triode amps, its not really an issue, provided the same tube / B+ is used on
all the RF decks. What I have learned..the hard way, is when using
HV in one box, and the RF deck in another box, the B- connections have to be
100% rock solid. I once had the B- open ( forgot to connect it) on back of
a 4-1000 amp. With B+ on, the cathode tries to assume full B+ value.
The bypass caps at the cold end of the bifilar fil choke started to crack and
explode ! Had a similar problem when the black B- millen connector went open
on a 6m GS35B GG triode amp, all hell broke loose. That, and make sure
u have solid bonded chassis ground connections to each RF deck. I used a
combo star ground and also bonded between decks. Then the plate /grid / B+
metering stays normal. With paralleled 6A10s between B- and chassis, and fault
current from a B+ arc to anything... just flows from chassis... up through the
6A10 diodes, back to B-...... completing the loop. 50 ohm glitch + also B+
fuse in HV supply do their job. If B+ fuse opens up, then all 1-6 RF decks
will have their PO drop to zero. With drive applied, and no B+... the grid
current meters will all peg, so you either require grid over current
protection..and /or a scheme that kicks all 1-6 amps offline, when B+ is
below a certain threshold.
## IMO, IF one is going to use 2-6 identical RF decks, ( or 6 x monoband RF
decks), with same tubeS, its more cost effective to build one big B+ supply vs
2-6 smaller B+ supplies. I have found that 6A10 diodes can be paralleled
and the current split is always 50-50..or at worse 48-52. 3 of em will split
evenly..as will 4. I have paralleled the 6A10 diodes on a FWB..and also a
FWD. Also what works is paralleling 2 x identical FWB assys. Of course any
HV filter cap assy has to be able to handle the ripple current.
## I looked at the pix on ur supplies. Your work over the years always
impresses me....superb metal work and construction.
Jim VE7RF
From: MU 4CX250B
Sent: Wednesday, November 30, 2016 8:36 AM
To: Jim Thomson
Cc: amps@contesting.com
Subject: Re: [Amps] Single Band Amplifiers One Power Supply
Running multiple RF decks simultaneously from one HV power supply is a bit
trickier than it might seem at first, especially if you want individual
metering on each RF deck. Grid-driven tetrode amps with grounded cathodes
introduce another complication, especially if mixed with triode amps. Also,
keeping track of the fault currents from flashovers or internal tube arcs and
keeping them from damaging anything can be a challenge. It can be done, but
it's just a bit harder than one might think at first. Here is a photo of two HV
power supplies I built recently, each designed to operate three RF decks.
http://www.w8zr.net/homebrew/HV%20Power%20Supplies.html
Details are in a QEX article I wrote a couple of years ago, and I'm happy to
send a copy to anybody who wants one.
73,
Jim w8zr
Sent from my iPhone
On Nov 30, 2016, at 7:36 AM, Jim Thomson <jim.thom@telus.net> wrote:
Date: Sat, 22 Oct 2016 19:07:58 +0000
From: Bill Turner <dezrat@outlook.com>
To: Amps group <amps@contesting.com>
Subject: Re: [Amps] Single Band Amplifiers One Power Supply
On Wed, 19 Oct 2016 18:47:05 -0500, W7RY wrote:
How would you go about metering them?
REPLY:
In modern amps. both the B- and B+ are NOT connected to ground, but
left floating. The grid current meter is connected from B- to ground.
The plate current (actually cathode current) meter is connected in the
B- lead BEFORE the grid current meter , i.e. on the power supply
side of the B- lead, not the cathode side.
Sounds weird, but it works. Check the schematic of any late model
grounded grid amplifier and that's how they do it.
If you want to use a single switched meter for all the amps. simply
put a low value resistor on the order of one ohm or so where you would
normally put the meter and them simply measure the voltage drop across
it. That way you can switch the meter from one amp to another without
disturbing current flow. Simple Ohm's law will give you the values.
73, Bill W6WRT
## The plate meter will only read plate current, and not cathode current.
The grid meter
will only read grid current. This assumes u wire the meters like have been
shown in every arrl
book for years.. for a GG triode. POS of both plate and grid meter bonded
together...then off to the
CT of the fil xfmr. Neg off plate meter to B-. Neg of grid meter to
chassis.
Jim VE7RF
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