[RTTY] Heathkit SB-1000 On RTTY

[Joe Subich, W4TV]

> In our discussion regarding the SB-1000 all the above is irrelevant
> anyway since the SB-1000 does NOT run class C. Use the specs for
> class B (older data sheet) or class AB2 (newer data sheet) and you
> will see the tube is fully capable of 600 watts RF output.

No, it is all relevant since the SB-1000 does not maintain 13.0 CFM
air flow in a pressurized cooling system.  The SB-1000 is cooled by
an axial fan.  Since there is no way to determine the actual air
flow in the SB-1000 cooling system, unless you can measure the base
base (200 C max) and plate (225 C max) seal temperatures under heavy
RTTY operation, it is only prudent to derate the tube to constant
carrier conditions.

73,

    ... Joe, W4TV


On 9/25/2012 3:11 PM, Bill, W6WRT wrote:
> ORIGINAL MESSAGE:
> On Tue, 25 Sep 2012 11:31:02 -0400, W4TV wrote:
>
>> Plate current is plate current, plate dissipation is plate dissipation
>> no matter what the class of operation. In fact, since an amplifier is
>> slightly more efficient in Class C than in Class AB2, the tube should
>> be derated even more in class AB2 than in class C.
>
> REPLY:
> You're missing the point. It's not just the class of operation, it's also the
> mode of operation. Class C plate modulation is far different from Class C CW or
> RTTY operation. With Class C plate modulation the instantaneous plate current
> and plate voltage swing up MUCH higher than the no-modulation condition. That's
> why PLATE MODULATION ratings are so highly de-rated.
>
> In our discussion regarding the SB-1000 all the above is irrelevant anyway since
> the SB-1000 does NOT run class C.   Use the specs for class B (older data sheet)
> or class AB2 (newer data sheet) and you will see the tube is fully capable of
> 600 watts RF output.
>
> 73, Bill W6WRT
>
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