[R-390] R-390 Digest, Vol 108, Issue 15

[bonddaleena at aol.com]

When I put my 390A into it's cabinet, I added 2 small 12 VDC muffin fans. One on each side, one blowing in and one out. Made a huge reduction in heat and you cannot hear them run.
I started down this road when I put my forearm across my Drake TR-6 that was being used for a long MS session.
19 tubes in that small package makes a great shack heater... ha ha

ron
N4UE

 

 

 

-----Original Message-----
From: r-390-request <r-390-request at mailman.qth.net>
To: r-390 <r-390 at mailman.qth.net>
Sent: Sun, Apr 21, 2013 2:29 pm
Subject: R-390 Digest, Vol 108, Issue 15


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Today's Topics:

   1. Re: thoughts on tube shields (wli)


----------------------------------------------------------------------

Message: 1
Date: Sat, 20 Apr 2013 12:27:03 -0700 (PDT)
From: wli <wli98122 at yahoo.com>
To: "r-390 at mailman.qth.net" <r-390 at mailman.qth.net>
Subject: Re: [R-390] thoughts on tube shields
Message-ID:
	<1366486023.45998.YahooMailNeo at web125306.mail.ne1.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1

Thinking about thermal issues, it occurs to me that we must recognize that half 
the tubes are up-side-down once all the modules are mounted inside the R-390A.

So for the tubes that are on the top deck, heated air from the tube shields will 
rise through convection, and conducted heat could go to the chassis. Heat 
conduction to the chassis frame is why IERC shields were designed to be mated to 
an IERC mounting collar held to the chassis by the tube socket bolts. At 
hamfests, these collars are rarely found, as uncommon as any IERC tube shield. 
Its importance is often overlooked. Without the collars, heat dissipation 
through conduction is small. 

For tubes on the bottom deck (audio deck and power supply) convectional currents 
will also rise... to the chassis frame itself and the large power transformer 
case, both which act as kind of a heat sink. Here, for conduction to work 
optimally, the IERC mounting
 collar is required. It is designed to conduct heat directly to a chassis. 
Without the collar, the only way for heat from the shield to dissipate is 
through convection. Note that the 26Z5's are real heat producers and are 
underneath. Conversion to silicon rectifiers should reduce heat production.

We agree that for best heat conduction from the tube to any shield, some 
mechanical contact to the glass envelope is required.? Shiny shields are bad as 
they reflect heat back into the tube, as Chuck and others have noted. 

Compared to high-end audio amplifiers or transmitters, these receivers do not 
produce all that much heat. The R-390 with its 6082's are another matter. Heated 
trapped air inside the cabinet can also be detrimental, making the addition of a 
small quiet muffin fan logical. 

W. Li
Mercer Island, WA


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End of R-390 Digest, Vol 108, Issue 15
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