Hello all,
I just picked up a Dentron Clipperton L the other day and I am having
some problems with it. It has the Harbach power supply board in it
and supposedly a set of good Taylor 572B tubes in it. The amp was
supposed to be working before it was shipped to me. It does not have
the tuned input board, so I am using a manual tuner between the radio
and the amp. It is wired right now for 120 VAC.
HV measured with a x1000 HV probe shows ~2774 V in the SSB position
and ~1810 V in the CW position. The tubes appear to have an idling
plate current of around 50-60 mA - measured by the Dentron´s meter in
the Ip switch position.
Even with 90+ watts of drive, I am unable to get more than about 220
mA plate current. The plate current goes up in proportion to drive
level, but the position of the TUNE and LOAD caps make very little
difference in plate current. In the CW mode position with 90 watts
drive, I get about 95-100 watts output from the amp. The position on
the TUNE cap makes a big difference in power output. The LOAD cap
makes much less difference, but the maximum power output occurs with
the LOAD cap fully meshed. Selecting the SSB mode position on the amp
gives only a little more plate current than the CW mode position (~250
mA instead of 220 mA) and no change in power output. This is with the
amp operating into a 1.5 kW 50 ohm dummy load.
There was no obvious shipping damage and the amp was packaged for
shipping well. I cleaned and checked the T/R relay and verified that
it is working OK. I checked the bias voltage at the 9.1V zener and it
is about 8.1 V when the amp is keyed. I checked the plate blocking
cap and it reads 994 pF on a cap meter. The tank circuit and switches
all look to be OK. All tubes have HV when checked with the HV probe
on each tube´s anode.
I removed the tubes and placed them in the amp one at a time. The
idling plate current looked maybe to be about 15-20 mA with one tube
and went up in proportion as each tube was added for a total of around
50-60 mA with all four tubes. The total plate current that I can
achieve with drive goes up in proportion with each tube for a max. of
around 220 mA in CW mode with four tubes. No matter how many or which
particular tube, the amp behaves the same as far as the TUNE and LOAD
making very little difference in plate current as well as the output
power being about the same as the input drive power. In other words,
the amp seems to be producing no gain. The tubes don´t show any red
on the plates and do not have any visual appearance of being gassy at
max. HV.
Can anyone familiar with the Clipperton L give me any suggestions on
what to check? I am kind of flummoxed at this point. Thanks for any
help or suggestions.
73 Phil N8VB
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15/08/2013 09:31
My friend's Clipperton-L had low output and didn't react normally to
load and tune adjustment. The doorknob capacitors in the tank circuit
were bad. Just an idea.
I believe he later changed the plate choke for another type as well.
--
Best Regards,
Chris Wilson.
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