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@post.com [mailto:johndtate@post.com]
Sent: Thu 2/18/2010 6:27 PM
To: Steve Katz; amps@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 <stevek@jmr.com>
To: TexasRF@aol.com; johndtate@post.com; amps@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@contesting.com on behalf of TexasRF@aol.com
Sent: Thu 2/18/2010 5:34 PM
To: johndtate@post.com; amps@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@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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