[Amps] Dentron MLA2500

[Keith Dutson]

During Field Day 2005 I ran into a similar situation with an Icom 775DSP and
a 40M Yagi.  The Yagi VSWR was about 4:1 and the auto tuner in the 775 could
not compensate.  Thus the power was dropped significantly to protect the amp
circuit.  I inserted a separate tuner but could not match the antenna with
this drive condition.  The front panel tuner switch was used to turn off the
tuner, but it would automatically re-engage when it saw the high VSWR.  I
desperately looked for a menu to disable the 775 internal tuner but could
not find one.  Frustration!  After a bit of luck I managed to guess the
proper manual tuner settings to get VSWR below 2:1 (tuned for max noise in
receive), turned the auto tuner off with the switch on the front panel, then
proceeded to fine tune down to 1:1.  We had to be careful when tuning around
the band to re-adjust the manual tuner.

Later, back at the shack, I looked in the manual and found there is a menu
item to deactivate the auto tune feature.  When I went menu searching again
on the rig I discovered the menus did not match the manual.  I did a system
reset and voila, there were the proper menus.  The auto tune feature is now
deactivated.  The front panel tune button can still be used to temporarily
engage the tuner.

73, Keith NM5G

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of rees.a at btconnect.com
Sent: Tuesday, October 25, 2005 12:51 AM
To: amps at contesting.com; rees.a at btconnect.com
Subject: Re: [Amps] Dentron MLA2500

Hi all
Thanks to everyone who replied.

The amp is delivering 900-1.2Kw on all bands 160-10, except for 80M.

Tuning on 80M with low drive (to avoid the auto ATU) gets me about 250W
before the Auto ATU kicks in. Problem with the 756 is that its too clever
for its own good, as I can't disable the Auto ATU. 

So tonight, I'll try a manual ATU between the 756 and the Amp. I have tried
different patch leads (as someone suggested) thinking I had an intermittent
connection, but no joy. 

A few people mentioned modifications to the input. I would be grateful to
see these, so can you mail them off list ?

Thanks

Adrian Rees (M1LCR)
Original Message:
-----------------
From: Henry  Pfizenmayer pfizenmayer at worldnet.att.net
Date: Mon, 24 Oct 2005 17:56:52 -0700
To: rees.a at btconnect.com
Subject: Re: [Amps] Dentron MLA2500


Adrian  - something worth trying which is pretty easy to do is to add about 
double the length of coax you have between the amp and the 756 - it just 
might help (or it may hurt other bands so you have to check them again ) - 
not very scientific but it sometimes solves these sorts of issues .

 As they say , your mileage may vary !!!!

73 - Hank K7HP


----- Original Message ----- 
From: <rees.a at btconnect.com>
To: <amps at contesting.com>
Sent: Monday, October 24, 2005 1:26 PM
Subject: [Amps] Dentron MLA2500


> Hi
> I have a Dentron MLA2500 Linear. I use an Icom 756PROII as the main rig.
>
> I discovered a problem the Dentron MLA2500 amp. On 3.5MHz my 756proii 
> won't
> auto tune to the input of the amp, therefore shuts off the drive. The
> reason being is that the 756 "sees" a high SWR.
>
> (All other bands work FB)
>
> I lifted the covers off, to discover the 100 Ohm swamping resistor had 
> come
> loose (dry joint..age whatever) so I soldered it back on.
>
> No improvement at all.
>
> Looking at the circuit diagram of the Dentron , there is no tuned input
> stage to the amp.
> I am somewhat befuddled by this. Any ideas ?
>
> By the way, all the tests where into a 2Kw Oil filled dummy load, with an
> SWR of 1.1:1.
> (Switching the amp to Standby (by passing the amplifier, and direct to the
> dummy load, and the 756 tunes OK, as you would expect).
>
> Thanks
>
> Adrian Rees (M1LCR)
>
> PS I have another Dentron ML 2500 Amp, that is FB, but doesn't cover 
> 28MHz,
> I believe it was made for the US Home market ? Any info about thhis
> appreciated.
>
>
>
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