[Amps] Single Band Amplifiers One Power Supply

Wed Nov 30 12:20:41 EST 2016

##  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 at 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 at telus.net> wrote:

  Date: Sat, 22 Oct 2016 19:07:58 +0000
  From: Bill Turner <dezrat at outlook.com>
  To: Amps group <amps at 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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