[Amps] measuring cap value

[Jim W7RY]

Just an old 2K or is there a suffix? The 2K, which I have on here, has no 
fixed caps in it except for the plate blocking caps.

Does it do it on all bands? Was this amplifier working? Are the settings 
exactly the same as when it was working? Have the "dials" slipped and now 
the position of the caps is anyone's guess?

73
Jim W7RY


-----Original Message----- 
From: Jim Hoge
Sent: Sunday, March 23, 2014 12:44 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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