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

johndtate at post.com johndtate at post.com
Thu Feb 18 15:30:43 PST 2010

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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