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

Thu Mar 18 03:59:24 PDT 2010

Will

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
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> VHFcontesting at contesting.com <mailto:VHFcontesting at contesting.com>
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