Re: [Amps] 4-1000A in Passive grid-driven use?

[R.Measures <r@somis.org>]

On Apr 29, 2004, at 10:03 PM, n7ioh wrote:

>    "Original post"
>    Are there any problems in using the 4-1000A in a passive 
> grid-driven mode on 160 - 10 meter or on 6 meters?  If not, what kind 
> of output can I expect to get?  Second, I have seen amps that use a 
> roller inductor and not a band switch, any thoughts?
>                        Thanks, Al N7IOH
>
>
>    Thanks Rich and Traian for your input to my questions.  Rich, it 
> seems like I read some time back where you said something about using 
> the same cooling method on this tube as that used on the SB-220, I 
> think.  I am not familiar with the cooling system on this amp, can you 
> elaborate a little or give me a recommendation.

  Cooling in the SB-220 is accomplished by taking advantage of the 
aerodynamic reality that horizontal airflow across a vertical cylinder 
produces semi-equal airflow 360º around the cylinder.  To achieve the 
needed simultaneous airflow across the filament pins (#1 and #5), Heath 
used a split chassis so that the tips of the fan blades pump air on the 
filament pins below the chassis while the rest of the fan cools the 
glass envelope above the chassis.  And, as an Absolutely free added 
bonus, horizontal air flow works better with the horizontal cooling 
fins on the anode cap,
--  However, this system only functions properly with a flat ceramic 
socket, not an "Air System" one.  For a 4-1000A/8166, it might be 
easier to use two fans, a a 150mm or more dia.  fan above the chassis 
to cool the glass envelope and a 50mm fan below the chassis to cool the 
filament pins.  I would choose DC brushless fans to do such.  A DC 
source can be obtained from the 7.5v AC filament winding to power a FWD 
rectifier/C-filter.
--  Since most of the cooling for a 4-1000A is accomplished by anode 
IR-radiation, it might not be a bad idea to paint metal surfaces 
adjacent to the anode with flat black paint -  such as Kenwood wisely 
did in the TL-922.  

cheers, Hal

> I don't want to damage the tube so I want to make sure I cover all the 
> bases in my planning before I start the building.
>
>                                        Thanks again, Al N7IOH
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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