> 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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