[Amps] 120 cycle hum from Henry 2K-4

[TexasRF at aol.com]

John, every dc power supply has some ripple. If the power supply has a  
nominal output of 2500vdc and the ripple voltage is 125 vpp then that would be  
5% peak modulation or 3.5% rms. I think this is 20log .035 or 29 dB below 
the  carrier in this case.
 
So, how many dB down do you think your hum level is?
 
I don't know how to calculate ripple on a Henry type power supply; perhaps  
some here knows how or has actually measured one.
 
73,
Gerald K5GW
 
 
In a message dated 2/18/2010 5:31:28 P.M. Central Standard Time,  
johndtate at post.com writes:

I just  acquired a Henry 2K-4 console linear amplifier.  I like to run 
AM as  well as the other modes.  The Henry is rated for continous duty 
and  as AM is closer to continous than SSB, I figured it was a good amp 
to  have.  I'm very satified with the output from the two aging Eimac  
3-500Z's but the 120 cycle hum that rides on the carrier is  
troublesome.  It's there whether I'm using my Kenwood TS-570 or my  
modified Heathkit DX-60 to drive it.  When I use the DX-60 (which I  
prefer for AM) making adjusting the tuning control will change the  
amplitude of the hum but never reduce it enough.  Seems like when in  
resonance the hum peaks too.  I have grounded the amp and the DX-60  via 
10 gauge solid copper to an 8 gauge solid copper coming into the shack  
that's attached to the 8 foot copper clad steel ground rod right  
outside a couple feet away.

For some perspective, I have no audible  hum from the Heathkit SB-200 
and everything else the same.  The  SB-200 is setup for 120 volts 
however, not 220/240.

The Henry has  full-wave bridge rectifier then uses an 8 henry (700ma) 
filter choke with  an oil filled .1mf (7500v) in parallel then an oil 
filled 20mf (5000v) cap  to ground.

I've been told those oil filled caps rarely go bad and  usually last 
longer than we do.  Any clues where I should be looking  to solve this 
hum problem?  Of course it's not really noticible on  SSB but I'm sure 
it's in there as well.

73 and thanks for any tips  and patience with this !
John   KX5JT

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