Gerald,

Yea, as long as it runs within the ratings, it'd be ok. That makes 
one wonder if Eimac might have made an over-kill on the radiator of 
the 4CX1500.  I'd have to see what Eimacs temp specs are for it as 
compared to the GU-84B, plus there's a 100 watt dissapation 
difference there too. I wonder if the guts in the GU-84B are maybe 
beefier than the ones in the 4CX1500? What I'd read is they were 
almost identical except for the radiator size. If the GU-84B runs 
as cool as the 4CX1500 with the same cooling arrangement, that 
would tell the tail. But, if it ran hotter, I'd say it would sure 
need more air to operate the same. I'll try my best to find that 
article where I read about the differences if I can and post it 
here. It's was a while back so I may not be able to find it on the 
net.

Best,

Will


----- Original Message -----
From: TexasRF@aol.com
To: craxd@engineer.com, Amps@contesting.com
Subject: Re: [Amps] GU-84B Cooling
Date: Wed, 20 Jul 2005 07:56:21 EDT

>
> In a message dated 7/20/2005 3:13:43 A.M. Central Standard Time,
> craxd@engineer.com writes:
>
> Dick,
>
> I'm not saying it's a bad tube, and dont want none to  think that. I just
> dont want anyone to undercool the tube so it will last. Who  
> knows, the 4CX1500
> may have an over-sized radiator too! About the only way to  tell 
> about the temp
> would be to use a thermocouple connected to the anode.  Then the temp read
> under contesting conditions both under SSB and AM using the  air flow they
> recommend. AM/CW creates a good bit more load on one as does SSB  
> transmissions.
> Then if the temp stays down where it should, one would know it  
> would be ok. I'm
> like Rich, and what George mentioned, use the largest blower  possible.
> Another thing too is maybe mount and external blower and duct it 
> to   the amp. You
> can set one of these in another room to help kill the sound down  if it's a
> concern. On yours, you may have the right combination by using  
> enough fans both
> pushing and pulling. Have you measured what the air flow and  pressure is on
> your amp? If so, let us know so we all have a starting  point.
>
> Best,
>
> Will
>
>
>
>
>
> GU84B data at the ND2X website shows 57 cu ft per minute air flow at 1.2"
> back pressure. There are Dayton blowers readily available from 
> Grainger Supply
> that will do this.
>
> Running the tube at 3000v, 1.7A , class AB1, locked key, would generate a
> heat load of about 1900 watts.
>
> Using the heat rise equation from the ARRL Microwave/UHF Experiments  manual,
> room temperature into the tube would exit at about 190 degrees F (88  degrees
> C).
>
> This sounds like a reasonable scenario doesn't it? AM linear operation will
> back the dissipation way down as would cw or ssb.
>
> Doesn't seem even that multiple blowers would be neeeded.
>
> 73,
> Gerald K5GW


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