Hi Martin - most probably you will find that the amp has a decoupling
capacitor (about 0.01uf) from the line and neutral terminals to ground
(chassis) to bypass any rf on the mains lead. This will develop half the
supply voltage on the chassis and must have a good solid ground to the
supply earth. Yaesu FL-2100 amps have a similar arrangement with a 2 core
mains lead and give you quite a "kick" if you touch something which is
grounded! You have done the right thing in connecting the case to ground.
BTW in this country and the UK it is illegal to use a 2 core mains lead
with any exposed metalwork which is not grounded.
John ZS5JF
----------
From: Martin Gary <n3hrt@us.hsanet.net>
To: amps@contesting.com
Subject: [AMPS] A few questions
To: <amps@contesting.com>
Date: 17 December 1998 07:54
I recently acquired a Henry 2k-3 amplifier. It uses 2 3-500z's. I get good
power out and it works very well, however, there are a few things happening
that concern me.
1) When I got it home and plugged it in, I happened to touch the case and
another radio that was grounded at the same time. Got a pretty good shock
(not a lot of current). So I measured the voltage on the case of the amp to
ground. 115 vac. The amp is wired for 220 vac. I checked over the schematic
and the way it was wired the case was not grounded. I called Henry (got
someone who could barely speak English) and they said that I should connect
a jumper from the common wire on the 220 line coming in to the case of the
amp. I did that and that fixed the problem. I still think that there could
be something wrong.... why would there be voltage on the case in the first
place? Leaky transformer?
2) I have a slight amount of 60 Hz hum in the RF out of the amp. Its not
much but its there. I put a cw signal into the amp and sure enough the
output waveform is modulated with ac looking at it on a scope. I thought
that I might have a ground loop in the shack so I went outside and
connected my tower ground (there are 5 ground rods driven around the base
of my tower in a 24 ft radius) to the power company ground. I have known
for a while that there was a little bit of current flow from my ground to
the power company ground. Anyway, this did nothing for me, I still have the
same problem.
I think that these two problems are related, but I have no idea how to cure
it. I suspected that I might have a bad filter cap, I checked the high
voltage and it reads 3200 volts... about what it should read. According to
the front panel meter the voltage drops by about 300 volts with full power
output. Not real good regulation as far as I'm concerned but the high
voltage is still within spec. The book says it should be between 2800-3200
volts. The high voltage filter cap is a 20 uf oil filled cap. I have never
seen one go bad......that doesn't mean they don't I just haven't witness it
in the last 20 years of being an electronic technician.
I'm hoping that you amplifier experts can shed some light on the subject.
Thanks for reading this.
Martin - N3HRT
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