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[Amps] power limiting in 8410 amps?

To: <>
Subject: [Amps] power limiting in 8410 amps?
From: "Jim Thomson" <>
Date: Tue, 6 Nov 2018 07:14:18 -0800
List-post: <>
Date: Sun, 4 Nov 2018 20:49:18 -0600
From: Jim <>
Subject: Re: [Amps] power limiting in 8410 amps?

<The Drake L4B only need 2-4 diodes for bias. The less ZSAC the harder it 
<is to drive.


<Jim W7RY

##  I have bucket loads of drive form the  200+ watt output xcvrs.   I 
installed  a 
miniature spdt CENTER OFF   toggle switch on the rear apron of the L4B  RF deck.
Then used the  switch to tap the  string of  10 x diodes.     Center off 
position  means
all 10 x diodes in the  circuit.   Other 2 x positions  tap the string at  4 x 
diodes..and  7 diodes. 

##  with all  10 diodes in the circuit, idle is reduced to just 100 ma with B+  
in ssb position ...  2650 vdc. 
And  just 40 Ma...when   B+  is in CW position....  1900 vdc.     Zero 
complaints of  IMD  since day 1.
Depending on MU of tubes used,  the thought was bias would need to be tweaked a 
bit.   With the grids
directly bonded to chassis, tubes like  4-400  A /B/C  can also be 
which case, they would be  run zero bias.

## The extra  drive power to overcome the added bias of say  10 x diodes..vs   
2 x diodes is not very much,  10 watts. 
  100  watts =  80 volts into 65 ohms.  65 ohms is what the cathode Z is. 
110 watts  =  84 volts  into 65 ohms.    The extra  6  diodes is just   6 x 
.725 V  =  4.35 volts.   Another  10 watts required
to ovecome the 4.35 volts of extra bias. 
  But, the Drive power is reduced a bunch,  typ  20-25 watts... when all 6 x 
grids are bonded to chassis. 

##  On a side note, if the choke is removed from the grid pin on each tube.. 
carefully   remove it, as they
are  good quality chokes.  Forget the exact inductance, but the   DC resistance 
is only .9 ohm  on them, which is superb. 
The chokes used on the heath  SB-220  measures  25 ohms.    

Jim   VE7RF

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