[Icom] RE:R9000 and 781 heat

Wed, 9 Oct 2002 08:51:00 -0400

Hello Adam,

I had been running my 781 down around 105 volts to help reduce the heat
problems.  It appears to work fairly well, however it will distort the
center point of the display freq on the scope.  This can be adjusted
internally, but I was just living with it.
I spoke to a well known Icom service tech (independent) and he advised
that the rig be run at the higher input voltage, say 115 to 120 since
the low voltage will compromise other functions of the radio.  I am
confused on this issue since the specs claim to have an operational
mains voltage range of 100 to 120v.  

What issues is this tech concerned with?  Any ideas?  
Bruce K1XR

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Adam Farson
Sent: Wednesday, October 09, 2002 12:40 AM
To: [email protected]
Subject: RE: [Icom] Re:R9000 RECIVER TT-340

Hi George,

Oops! You are correct. I miscalculated (V2)/R - I eat a kilo of humble
pie
before thee. Reducing the mains voltage to 100V will largely eliminate
the
IC-781 heat problem; I would advise your friend to power his radio via
an
autotransformer.

Were the new Icom radio to pip the Orion at the post, it would then
surely
be time for the Tennessee equivalent of honourable seppuku in Dolly
Parton
country!

Cheers for now, 73,
Adam VA7OJ/AB4OJ

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of George, W5YR
Sent: Tuesday, October 08, 2002 21:29
To: [email protected]
Subject: Re: [Icom] Re:R9000 RECIVER TT-340

Now you got me nit-picking!

If the line voltage is increased from 100 volts to 120 volts that is an
increase of 1.2. The power associated with a 1.2 voltage increase is the
square of the factor or 1.44 assuming that the load current increases
proportionally, i.e., the load remains a constant resistance, as it
were.

Would this not translate into a 44% increase in heat dissipation as well
as
supplied power to the rig?

What in the 781 power circuitry acts to limit the power/dissipation
increase to only 20%, the same factor as the voltage increase?

Enquiring minds want to know . . .   <:}

Seriously, I have a good friend with a mint 781 who might want to use an
autotransformer to drop the line voltage down to 100 volts. My line
voltage
here is an almost constant 123 volts.

Is the over-voltage a serious enough problem to warrant dropping the
supply
voltage?

On the TT front, wouldn't it be something if Icom got their new radio to
market before the dust settles on the Orion and TT finally have a
reliable
working unit available in quantity?

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas

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