[Amps] Dentron Clipperton L Problem

[n8de at thepoint.net]

What band?

If this is occurring on 160m .. check the plate loading caps and bandswitch.

If it occurs on 20 - 10m, the problem is probably the bandswitch.

73
Don
N8DE


Quoting Chris Wilson <chris at chriswilson.tv>:

>
>
>> 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
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
>
> 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.
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>