[Amps] henry amp problem

[Zev Darack]

I was looking into a similar problem with 2 other Henry Desktop amps having
no output.  I found this on the web but have not had a chance to review it
yet.  These seem like a pain in the butt to disassemble:

Source: W1QJ
"For the Henry fans out there. There is one common problem with just about
all Henry amps that have the load capacitor below the RF deck chassis.
Henry had a very poor design that eventually failed in amps that were run
on high duty cycle modes like contesting and rtty etc. The defect in the
design is how they brought the connection from the tank coil above the
chassis through to the load cap below the chassis. If you look toward the
back of the roller inductor just below the center line down at chassis
level, you will see a ceramic feed thru. A copper strap will be connected
to the top of the ceramic insulator and on the bottom it connects to the
load cap. The problem is that the ceramic feed thru is not RF rated with a
zinc plated screw or even a SS screw. The screw is very lossy at RF and
heats up real bad. The heat stresses the ceramic and it causes minute
cracks. The RF eventually arcs thru the cracks to ground and the screw
beigins to deteriorate. I have repaired 2 Henry amps already with the
symptom of loss of power for no apprent reason. Now the rub is, if you look
at the ceramic insulator it will look just fine on both sides of the
chassis but the center of it will be burnt out and the screw will almost be
eaten through. The screw is a small #6 screw and it can't handle the power
at RF. You have to remove the insulator and check it. The 2 I fixed both
looked good from what you can see of it but the problem is right in the
center where it passes through the chassis. You can't see that part of it
unless you take it apart. The last one I fixed the #6 screw in the middle
was about the diameter of a toothpick. I did not repair it with a new
insulator, I used a piece of center conductor from RG-8 poly coax and made
the connection between the 2 points with that. After the repair both amps
had better output. I would check that insulator if it were my amp for good
measure."

On Thu, Dec 4, 2014 at 10:07 AM, Douglas Johnson via Amps <
amps at contesting.com> wrote:

>  During the cw contest my henry 2-kd classic started to act up, no power
> output on 40-80 meters and after 3 or 4 seconds transmitting on 20 power
> drops to zero. 10 and are normal output . plate current, plate voltage and
> grid current remain ok on all the bands and input tuning is normal on all
> bands. all power goes thru bird wattmeters and bird coax switches which
> have functioned fine for 35 yrs. I eliminated all of them with 1 coax and
> wattmeter into the dummy load, same results. At no time did I observe any
> noise or smell from the amp to indicate trouble, this amp is going to be a
> pain to remove and open up for repair so I hope to learn something before
> that has to happen,  any comments?....Doug, w9iix
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