>
> ----- Original Message -----
> From: "Jason Buchanan" <jsb@digistar.com>
> To: <amps@contesting.com>
> Sent: Sunday, November 13, 2005 1:40 PM
> Subject: [Amps] L4 power supply problem?
>
>
>>
>> hi,
>>
>> I have an L4 with its original power supply. Been working fine for a
>> long time.
>>
>>
>> Today, I turn it on and after a few minutes there is a large pop and
>> blue spark from near the HV interlock, or located behind the rear tube.
>>
>> The .82 ohm resistor fried - I replaced it with a new one and carefully
>> inspected here and there in the amplifier cabinet. I couldn't find
>> anything that burned near the interlock.
>>
>> I powered it back on in CW low voltage position and the plate voltage
>> reads around 1300V. On SSB it reads around 2000V, maybe a little less.
>>
>> That was all the experimentation I wished to try. I opened the L4-PS
>> and looked around but can't find anything on the top side that looks
>> burned or stressed.
>>
>>
>> The thing I noticed that was peculiar was that when I powered the L4
>> off, the plate voltage would begin to decrease as expected, but then
>> ROSE about 200 volts and then slowly decreased again as expected. When
>> I took the amplifier cover off there was still a bit of voltage in the
>> HV supply, around 150V on the meter. I used a pair of alligator clips
>> to ground the cabinet to the top of the plate choke and then removed the
>> clips - what was odd was that the voltage rose up to about 100V - when I
>> grounded it the meter read 0 again. When I removed the clip it rose to
>> about 50V. Finally I put the clip on and left it on and it finally
>> stayed at 0 with the clips off.
>>
>> Has anyone seen this before? Any idea what is wrong... and what I can
>> do to repair it?
>>
>>
>> 73 Jason N1SU
>>
Hi Jason,
Perhaps a shorted bleeder as the cause and now open?
Mike k1ern
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