Posted by
N2EY on
Sep 13, 2007; 11:59am
URL: http://elecraft.85.s1.nabble.com/Use-of-Heathkit-SB200-amp-tp452840p452841.html
In a message dated 9/12/07 11:12:05 PM Eastern Daylight Time,
[hidden email] writes:
> the Heathkit SB-200 has several
> modifications that can be made to it, one of which is the reduction of drive
> power to excite it.
What is modified to do this?
>
> Does anybody have any idea what the lowest power required to excite an
> SB-200 amp is?
>
I presume you meant "what the lowest power required to excite an SB-200 amp
to full rated output is"
The SB-200 uses a pair of 572B triodes in grounded-grid. The data sheets list
the 572B as needing 50 watts of drive in that service, so a pair will need
100 watts of RF to drive them.
> Without mods, it is around 100 watts, but I use to have one with the
> reduced
> drive mods, and I drove it with 30 to 50 watts for around 300 watts out.
The tube ratings (for a pair) say that 100 W of drive will give 600 W output,
so 50 W of drive would give 300 W output.
I don't see what could be modified to reduce the drive requirement for full
output, except perhaps changing to grounded-cathode operation instead of
grounded grid. But such a mod would be extensive, requiring neutralization and other
changes.
I
>
> never tried testing the lower end with that mod. Though.
>
> Bottom line is: if an SB-200 had the reduced drive mod, could a QRP K2 at
> 10 to 15 watts with an amp key interface safely/adequately drive an SB-200
> to say, 50 to 60 watts out?
>
Since the SB-200 is a linear amplifier, I don't see why not. Of course it's
using a sledgehammer to drive a 3d finishing nail....
The problem is, how do you tune up the SB-200 with such low drive power?
---
I'm curious to know what is changed by the "low drive mod" for the SB-200.
Thanks
73 de Jim, N2EY
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