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[AMPS] Re: Emtron fan noise (hk4cze)

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Subject: [AMPS] Re: Emtron fan noise (hk4cze)
From: laussana@epm.net.co (Jorge A Mejia)
Date: Thu, 25 May 2000 10:48:21 -0500
Hi Kim:
Many thanks for your valuable information. Yes I am in fact very dissapointed.
after spending over US$2000 and some there is no way I can  operate the DX1. It
goes to std by after a few words are transmitted. As per suggested by ZL1AMJ I
added another fan (piggyback) excactly like the original one but the noise is
unbearable, however the amp is clear of the overheathing situation. My model
should be one of the latest because I received it about a month ago or so. I
have tryed to contact Mr Breznek of Emtron, but looks like he is away from
Australia. Before I attempt to make the modification you suggest I would prefer
to see If I can get from the factory the fan that they use on the DX-2.
Hopefuly,Rudi will get back to me sometime. By the way I also use the amp with
an Icom 746, and a Ft1000.
I will look for you on 10mtrs.

73's Kim and Thanks again/ Jorge/ HK4CZE


Kim Rhodes wrote:

> Hi Jorge
>
> I have had an Email passed on to me regarding the DX1 fan noise.
>
> Well I think you have an older model like me as the new DX1 is to hav the
> same fan as the DX 2.  That would probably be the best option.
>
> I also have a problem with over heating and I live at sea level.  What I
> have done to solve the problem is:-
>
> First I have moved a link on the control board to remove the bias switching
> detection.  Its like VOX and brings the bias to a point where the amplifier
> is in my opinion running near class A.   So I have set the link to stay on.
> This initally causes tha amp to draw about 300mA without drive.  This is the
> plate current minimum when you talk now on SSB.  This causes a lot of heat.
>
> I have then adjusted to bias level to reduce the idle current to about 80mA.
> This sets the amplifier back to class B or perhaps AB.
>
> Now the amplifier runs much cooler but you will need more drive from the
> transceiver i.e 30 -40 watts  the output power is still the same but
> harmonics may be a little higher.
>
> On 29Mhz the higher drive caused a choke to burn out on the bias input and I
> have changed this for a different choke.
>
> Now it works well and I have not tripped off due to over temp since I made
> these  changes.  I also only run the original fan.
>
> Note this is not necessarily an approved change by the manufacturer.
>
> I have also modified the control board to stop the over drive lamp flashing
> on PTT.  This flash puts an ALC pulse out to the transceiver if you have ALC
> connected and caused problems with my ICOM 746.  I also added an resistor
> from the forward power detection to the ALC to provide a proper ALC output
> to hold down the drive.  Now I get a gradual ALC increase for power output
> instead of only getting ALC at the point of over drive.
>
> The ALC modifications have been passed on to Rudi and I think they are now
> implemented in the DX1.  I don't know if yours if changed or not it would
> depend when you got it.
>
> The bias change I have not bothered to pass on as I am really running the
> amplifier in a differnt mode than what Rudi intended.
>
> I am on 10M 28.488 at 0800 GMT most days and I monitor 28.885 earlier in the
> day most days.
>
> I can give you more detail information if you want to try what I have done.
>
> 73,s  VK6TQ  Kim


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