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

Thu Mar 18 11:52:06 PDT 2010

Okie Dokie

I've fitted the mains plug with a 13 amp fuse this time and put the lid 
on the amp so the micro switch is down which should allow me to transmit.
I have the lid down before I switch it on and wait for the HV to get to 
480 and the green light comes on, I go to operate and key up and nothing.

2nd time around I switch it on with the case open and the micro switch 
up and wait again go to operate and I press the micro switch down and it 
works
The amp transmits this way but not the 1st way so i've defiantly found 
problem.

Its as if the amp thinks the switch is up when its off and must pressed 
down whilst it's on for it to transmit.

Thanks
Will M0GYZ

On 18/03/2010 10:59, John Lemay wrote:
> Willa
>
> That little safety mechanism is designed to ensure that operation of the
> amplifier is not possible with the cover removed. It will ensure that at
> least some of the dangerous voltages are not present with the top off.
> Exactly which voltages are removed would only be evident with scrutiny and
> understanding of the circuit diagram.
>
> I think it's quite possible that moving the amplifier around will cause the
> case to flex a little bit, thus affecting the safety mechanism. Maybe the
> table top was a little bit warped ?
>
> As others have said, be very careful indeed inside this amplifier. 2kV will
> kill. In addition, if memory serves correct, mains voltages are present on
> the circuit board between the rear power connector and the front panel main
> switch. These voltages are present as soon as the amp is plugged in to the
> mains.
>
> Good luck
>
> John G4ZTR
>
> -----Original Message-----
> From: uk-contest-bounces at contesting.com
> [mailto:uk-contest-bounces at contesting.com] On Behalf Of Will M0GYZ
> Sent: 17 March 2010 23:23
> To: vhfcontesting at contesting.com; uk-contest at contesting.com
> Subject: [UK-CONTEST] A Weird Dressler D 200 S Linear Amp Problem
>
> Hi All
>
> Thanks for all the help
>
> I opened the case today to find to a little safety mechanism (which is
> connected by 2 red leads going to somewhere underneath to the right of
> the fan) which pushes down when the case is on otherwise the linear does
> not transmit so after pushing it down a couple of times seemed to fix it
> I must have been using it for at least 3 hours this evening without a
> hitch untill i moved to a more perminant location and then it stopped
> working again and when i pushed down the mechanism again with the linear
> in standby it all turned off and it turned out I blew a fuse in the
> mains plug which was only 5 amps.
>
> At least I think ive found the problem though which is step 1
> now for the solution
>
> Here is the Manuel for it
> http://www.qth.at/oe1cwj/Dressler%20Manual%20D70_eng.pdf
>
> and here is a better pic of the inside so you can see what i'm talking
> about
>
> http://img225.imageshack.us/img225/4453/dressler.jpg
>
> As you can see there is a yellow wheel like thing to the right of the
> fan with 2 red leads coming off it
> thats the safety mechanism
>
> Thanks
> Will M0GYZ
>
>
>
>
>
>
> On 17/03/2010 18:05, Paul Kiesel wrote:
>    
>> Hi Will,
>>
>> Check that the solder on the output coax connector  is not open. Some
>> brick amplifiers will "bend" when being moved around. Very often the
>> solder will fracture where the output lead is soldered to the
>> connector. Look closely as it is hard to see. Good luck!
>>
>> 73,
>> Paul, K7CW
>>
>>
>> ------------------------------------------------------------------------
>> *From:* Will M0GYZ<m0gyz at gb3hp.com>
>> *To:* vhfcontesting at contesting.com
>> *Cc:* uk-contest at contesting.com
>> *Sent:* Tue, March 16, 2010 12:54:46 PM
>> *Subject:* [VHFcontesting] A Weird Dressler D 200 S Linear Amp Problem
>>
>> 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
>> _______________________________________________
>> VHFcontesting mailing list
>> VHFcontesting at contesting.com<mailto:VHFcontesting at contesting.com>
>> http://lists.contesting.com/mailman/listinfo/vhfcontesting
>>
>>      
>
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