SB 200 question

[Garey Barrell]

Ray -

The reason you got "attacked" on the other list is that there had JUST
been an interminable argument on this exact subject that deteriorated
into wire loss, transformer loss, square law, and how power is
calculated....  It had nothing to do with you, you just happened to walk
in just as the dust was settling!

The simple answer to your question, which got lost in the dust over
there, is that there should be no difference in the plate voltage on
your meter with either 120 or 240V input.  The reason it is better to
run a big amp off 240 is that the current drawn from the AC line is
subject to resistance losses getting from your breaker box to the amp.
Since the current is roughly doubled at the lower voltage, these losses
not only get larger, they also are a larger percentage of the total line
voltage.  With a 1KW amp that isn't too far from the breaker box, on a
house circuit that doesn't have any other outlets on it, and #12 copper
wire properly installed, you probably wouldn't be able to tell the
difference.  On a house circuit that also happens to feed the kitchen
and den from the same breaker your amp is on, you might be lucky to see
95V AC at your amp "key down".!

Most likely the reason your voltage is low is that the resistors in the
amplifier voltage divider that feeds the meter have gone up in value,
making the meter read "low".  This is typical with carbon composition
resistors that were used in that era.  I suspect if you measured the HV
with an accurate external meter, you'd find the voltage is right where
it ought to be.  There is also the possibility that your friend's amp
has resistors that are a little low in value, making his meter read a
bit high!  The last possibility is that the filter caps in your amp are
dying, (likely by now if they haven't been replaced,) and just aren't
charging up to full voltage.

Some day when you're bored, take a look at the archives for the "other
list" for the last week and you'll probably understand why you got
"jumped"!!!   :-)

73, Garey - K4OAH
Atlanta


Ray Friess wrote:

> I'd like to ask a question and I am hoping it does not ignite a storm of
> profanity and protest
> as it did on the boatanchors forum....   I am not looking for an indepth
> discussion of theory
> or anything like that.  Just a quick, simple answer to a question that
> puzzled me tonight...
> so that I can get a quick idea if maybe my sb 200 is way below par.
> Perhaps a power
> supply problem....
> I dont know if this has come up here before or not .... I, frankly, dont
> get a lot of the posts
> here....
>
> I notice the SB 200 meter is calibrated up to 3000 volts for plate
> voltage...
>
> What should be the typical plate voltage reading on the SB 200 amplifier
> meter when wired
> for 120 volt transformer primary input?  I can't find anything on this
> in the manual.
>    Mine shows 1800 volts ... which, if loaded to the manual
> recommended 500 mils, would
> be about 900 watts ....    That makes sense because the SB 200  is a KW
> amplifier....
>
> However, my friend's SB 200 meter shows about 2300 to 2400 volts and his
> is wired for 220
> volts transformer primary voltage....     He says he gets about 750
> watts out when using about 80 to
> 90 watts out from the exciter...
>
> Does the house voltage it is wired for make a difference in what the
> plate voltage is and what it
> would show on the plate voltage meter scale?
>
> Thanks for any help.  I am sure, if this has come up before, we can
> dispose of it quickly without a lot of
> in depth theory discussion.....
>
>

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