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

Thu Feb 18 20:30:35 PST 2010

Maybe not the amplifier.  Hums can be really tricky.  When I did that 
check last night, I hadn't had the ground lug on the back of the Henry 
tied to my station ground.  I grounded it very well with 10 gauge solid 
copper to the station ground (the 8 foot rod in the ground right 
outside)   I just checked everything AGAIN and it looks like the hum is 
NOT audible to others now from the TS-570 in AM mode.  I can see a very 
small amount on the scope but it's not audible so... I checked again on 
the DX-60 and without the amp on... there was the ripple.  I think it 
IS 60 cycle.  Someone last night on the air said it was 120 cycle but I 
listened to a 60 cycle hum audio file from the internet and guess what? 
  Yep.  I think after all the Henry is amplifying the DX-60's hum.  
Maybe because the SB-200 has a grounded three prong 117 volt plug... 
and the shield from the coax does tie the chassis's together, the hum 
was reduced?  The DX-60 has a non-polarized 2-prong plug.  I looked 
closer at the DX-60 cw on the scope by itself and the hum is there.

I'm going to install a 3-prong grounded cord/plug on DX-60 and see if 
that works.  Hums can be really tricky to figure out!!  I think I'm 
finally on the right track and maybe it isn't the amp!!  It's a 
learning experience for me!  *crosses fingers*

-----Original Message-----
From: Steve Katz <stevek at jmr.com>
To: johndtate at post.com; amps at contesting.com
Sent: Thu, Feb 18, 2010 9:06 pm
Subject: RE: [Amps] 120 cycle hum from Henry 2K-4

Perfect!  Then, it must be the amplifier. 

Have you confirmed it's really 120 Hz and not 60 Hz?  If so, sounds 
like the choke tuning is incorrect and the tuning cap across the choke 
may have drifted in value.  Of course, it could be the main filter cap 
as well.

Oil filled caps do generally last a long time, but they can go bad.  
Have you opened up the power supply covers to look inside and see if it 
leaked?

-----Original Message-----
From: johndtate at post.com [mailto:johndtate at post.com]
Sent: Thu 2/18/2010 6:27 PM
To: Steve Katz; amps at contesting.com
Subject: RE: [Amps] 120 cycle hum from Henry 2K-4

Steve, It's also present in CW mode.  It's on the scope and it's heard
in my receiver and others.  It's present whether I use the DX-60 or the
TS-570 in any mode that produces a carrier, with or without audio.

-----Original Message-----
From: Steve Katz &lt;stevek at jmr.com&gt;
To: TexasRF at aol.com; johndtate at post.com; amps at contesting.com
Sent: Thu, Feb 18, 2010 8:08 pm
Subject: RE: [Amps] 120 cycle hum from Henry 2K-4

The Henry amps I've had (several over the years) when operating
properly produce negligible hum modulation at full rated power.

But I asked earlier if he found the same evidence of ripple when he
used "CW" (vs. "AM") on his exciter and I don't think I've seen that
answered.

If "yes," then it could well be a PS issue in the Henry; if "no," then
it's something else.  Usually if the PS develops unreasonable ripple,
its regulation will also suffer since they're both based on the same
factors.

Steve WB2WIK/6

-----Original Message-----
From: amps-bounces at contesting.com on behalf of TexasRF at aol.com
Sent: Thu 2/18/2010 5:34 PM
To: johndtate at post.com; amps at contesting.com
Subject: Re: [Amps] 120 cycle hum from Henry 2K-4

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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