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

[R.Measures]

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

>    "Original post"
>    Are there any problems in using the 4-1000A in a passive=20
> grid-driven mode on 160 - 10 meter or on 6 meters?  If not, what kind=20=

> of output can I expect to get?  Second, I have seen amps that use a=20
> roller inductor and not a band switch, any thoughts?
>                        Thanks, Al N7IOH
>
>
>    Thanks Rich and Traian for your input to my questions.  Rich, it=20
> seems like I read some time back where you said something about using=20=

> the same cooling method on this tube as that used on the SB-220, I=20
> think.  I am not familiar with the cooling system on this amp, can you=20=

> elaborate a little or give me a recommendation.

=F0  Cooling in the SB-220 is accomplished by taking advantage of the=20
aerodynamic reality that horizontal airflow across a vertical cylinder=20=

produces semi-equal airflow 360=BC around the cylinder.  To achieve the=20=

needed simultaneous airflow across the filament pins (#1 and #5), Heath=20=

used a split chassis so that the tips of the fan blades pump air on the=20=

filament pins below the chassis while the rest of the fan cools the=20
glass envelope above the chassis.  And, as an Absolutely free added=20
bonus, horizontal air flow works better with the horizontal cooling=20
fins on the anode cap,
--  However, this system only functions properly with a flat ceramic=20
socket, not an "Air System" one.  For a 4-1000A/8166, it might be=20
easier to use two fans, a a 150mm or more dia.  fan above the chassis=20
to cool the glass envelope and a 50mm fan below the chassis to cool the=20=

filament pins.  I would choose DC brushless fans to do such.  A DC=20
source can be obtained from the 7.5v AC filament winding to power a FWD=20=

rectifier/C-filter.
--  Since most of the cooling for a 4-1000A is accomplished by anode=20
IR-radiation, it might not be a bad idea to paint metal surfaces=20
adjacent to the anode with flat black paint -  such as Kenwood wisely=20
did in the TL-922. =20

cheers, Hal

> I don't want to damage the tube so I want to make sure I cover all the=20=

> bases in my planning before I start the building.
>
>                                        Thanks again, Al N7IOH
>
>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org