I just looked at the 2k4 manual. I never had one so I thought I'd look at the
schematic. I noticed something interesting. L10 ,a 50 uH choke, is connected
between the centertap of the filament transformer and the connection between
the two series connected filaments. If for some strange reason either tube is
drawing less than filament current than the other there would be a 60 Hz AC
current flowing thru the RF chokeL10 which I assume has a metallic core. If
that is the case the inductance of L10 could be modulated at a 120 Hz rate
causing an input impedance modulation thus modulating the input signal. This
is not likely but a remote possibility. Easily determined by measuring the AC
voltage across L10 with only filaments lit. And if you do measure a voltage
across it then measure it's resistance and calculate the current. Also, L10
may have been replaced somewhere down the line with a lower current one that
would saturate at a much lower 60 Hz current.
But odds are that it is plate supply ripple.
73
Bill wa4lav
________________________________________
From: amps-bounces@contesting.com [amps-bounces@contesting.com] On Behalf Of
johndtate@post.com [johndtate@post.com]
Sent: Thursday, February 18, 2010 11:30 PM
To: stevek@jmr.com; amps@contesting.com
Subject: Re: [Amps] 120 cycle hum from Henry 2K-4
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@jmr.com>
To: johndtate@post.com; amps@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@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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