[UK-CONTEST] A Weird Dressler D 200 S Linear Amp Problem

[John Wilson]

Will,

I think you might well have a dry joint or something similar.  The 
construction quality of these amps is not wonderful and I've had a 
couple of problems with mine. In fact when I last had to move the amp, I 
noticed that it sounded as if there was something a bit loose inside.  
On investigation it turned out that the wire at one end of the screen 
supply reservoir capacitor had broken.  It must have been like this ever 
since I'd had it, as after replacing it, the amp produced significantly 
more power.  Its amazing that it didn't have more effect on the signal 
as nobody had mentioned 50 Hz modulation.  Perhaps they just thought I 
had a rough voice...

To take this further you will need to take the covers off and have a 
good look round with the power off and see if there is anything 
obviously wrong.  Be very careful, unplug it at the mains and wait till 
the Hi voltage has dropped to zero on the meter and even then beware as 
the screen supply might still be dangerous.  If you don't find anything 
obvious I wouldn't take it any further than this unless you are 
comfortable working on equipment with high voltages - there's an awful 
lot of exposed Hi voltage and mains connections inside this amp.

73 John G3UUT

Alex GM3ZBE wrote:
> Erm...........It's not April 1st yet is it ?  :-)
>
> Will M0GYZ wrote:
>   
>> Hi All
>>
>> Got a weird one for you.
>>
>> I have Dressler D200S VHF Linear Amp which was given to me for contesting.
>> There has always been a strange problem which i originally thought was a 
>> sticky relay
>> However after a while of looking at it. Its as if the amp wont Transmit 
>> without it being on a really flat surface which caused problems for me 
>> at the recent 144/432mhz contest
>> I can't figure out why it would require such a dead flat surface before 
>> the needle moves and im putting power out.
>>
>> It was working ok apart from this at home as i was putting out 120w with 
>> 5w drive provided I found the right spot for it but when i took it out 
>> to the contest it just didn't want to Transmit at all and when it did 
>> the power just decreased over 3-10 seconds and I couldn't get 120w out 
>> of it max.
>>
>> My thoughts are thats it might be a dry joint but the guy who had it 
>> before me didn't ever report it had a problem but unforuntly he died a 
>> couple of years ago.
>> So it only Transmits when its in a spot it likes after moving around my 
>> windowsill
>>
>> So any thoughts  ?
>>
>> Thanks
>> Will M0GYZ
>>     
>
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