FWIW _ It appears with the help of several folks on this reflector and the
AMPS reflector the Centurion oscillation problem on 40 meters is resolved.
It also appears the "squeal " is fixed but may require a little more time to
be 100 percent sure.
Tentec service says the squeal is coming from the fan bearings and
recommends you take the label off the fan and tighten the screws behind the
label . This is a weird one as the pitch does not change when you turn off
the amp and the fan is running down - my fan spins for about 74 seconds
after turn off- TT says the one they timed was more like 3 minutes, so I may
have marginal bearings. This operation is a little bit of a pain as the fan
label and screws are right behind the RFC and parasitic suppressor assy, so
you have to remove the tubes and the rfc assy to get to the fan.
The solution for the oscillation on 40 meters was to increase the length
of coax between the Orion and the Centurion. One person also suggested a
W2DU type ferrite bead current mode "isolator". I had a Wireman balun good
to 160 so I tried that (that added about 3 feet to my already 4 foot long
jumper) and the oscillation stopped, and all bands were stable.
I wondered if maybe the real change was just the extra cable length so I
made up a 8 foot RG8x jumper and the amp was still stable all bands. When I
called Tentec to tell them about the solution - they said they normally use
about a 8 foot cable so they had never seen what I encountered with a short
interconnect.
So In summation.
Squeal - Tighten the screws under the label on the fan
40 meter oscillation - be sure you have at least 8 feet of RG8 or RG8X
cable between the exciter and the. amp
Thanks to all for the suggestions - looks like I am back in business.
Hank K7HP
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