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Re: [Amps] Single Band Amplifiers One Power Supply

Subject: Re: [Amps] Single Band Amplifiers One Power Supply
From: N7EME <>
Date: Wed, 30 Nov 2016 12:03:53 -0700
List-post: <">>
I have a 6 meter GS31B amplifier that I am running on a single power supply currently. The plan is to run a GS31B 2 meter amp and a GS31B70cm amp from the same supply. 2Meter amp is in design stages now and the 70cm is waiting for permission from FCC to run more than 50 watts in Arizona. For the 6 meter amp I monitor the HV coming into the amp along with a blower switch and an enable line for the amplifiers PTT circuit. If any of these conditions are not active, then the PTT is disabled preventing the G-G amp grid from being RF driven when HV or blower is missing. The 2 meter and 70cm amps will
have the same circuit.

Jerry - N7EME

On 11/30/2016 10:20 AM, Jim Thomson wrote:
##  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 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
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.

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.
Jim w8zr

Sent from my iPhone

On Nov 30, 2016, at 7:36 AM, Jim Thomson <> wrote:

   Date: Sat, 22 Oct 2016 19:07:58 +0000
   From: Bill Turner <>
   To: Amps group <>
   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?


   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 

   Jim  VE7RF

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