[Amps] measuring cap value

[Jim Hoge]

It's a 2K classic, mfg Jan 1997. The relays checked out with an ohmmeter but I have not tried cleaning the contacts- they appear to be sealed relays.

73,
Jim




On Monday, March 24, 2014 12:56 AM, David Harmon <k6xyz at sbcglobal.net> wrote:
 
Hi Jim....I'm pretty familiar with the Henry console amps.
I bought a 3K-A in 77' and still have it...I have had a 3K Classic MKll for
3 years and am very familiar with it as well.

Have you tried cleaning the make contacts on the antenna changeover relay??


73

David Harmon
K6XYZ
Sperry, OK


-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Jim Hoge
Sent: Sunday, March 23, 2014 2:44 PM
To: amp reflector
Subject: [Amps] measuring cap value

Hi gang,

In the course of trying to diagnose my Henry 2K floor model amplifier
issues, I have tried to measure the doorknob caps with an MFJ 269. I'm sure
this is far from ideal but it's the only device I have that can measure the
caps. The two parallel plate blocking caps are high on the list of suspected
failure. According to the MFJ 269, the caps are good but when sweeping the
frequency upward, the reactance goes out of range. I would think the
reactance would remain within the metering range of the analyzer for the
frequency range of the amp. The cap value is relatively good up to about 12
mHz before it is out of range. BTW, each cap was removed and tested with the
analyzer by leads of less than 2 inches. The two plate blocking caps as well
as the 5 switched caps that follow them measured nowhere within the +/- 10%
of the rated values. None indicated a short with the analyzer or an
ohmmeter.

Some background on the amp: In bypass mode, things are fine. In operate
mode, you can see a small dip in plate voltage and you can hear the amp go
under load. With swr/ power meters both between the transmitter and the amp
and between the amp and antenna, swr is normal but power output is about a
sixth of power input .The tubes have tested good in another amp. The relays
have been shown to be good. That is what brings me to the plate blocking
caps. The Henry employs a pair of HEC doorknob caps at 7.5kv and 1000 pf
wired in parallel.

In summary, will the MFJ suffice for ballpark measurements or will I miss
issues associated with the caps? Based on what I have measured, are the 2
plate blocking caps still suspect?

tnx es 73,
Jim W5QM
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