Dennis Sokol wrote:
>I have a BTI LK-2000 using a 3-1000Z operating on 160. I can get 1250 watts
>out with 2700 volts and 750 ma key down. The tube seems to be limited in
>current draw. I have seen more power out at a different QTH with higher line
>voltage.
>
Well if the anode voltage is higher, you will expect that, even if you
had the best stabilised heater supply in the world.
>I have measured the filament voltage at full load to be 7.08 volts.
>This is a bit low from the spec of 7.13 to 7.87 volts. Is the low filament
>voltage a possible cause of reduced power out?
>
I doubt it the filament voltage, but the plate voltage that is changing
your power out.
How consistant is your line voltage? In the UK at least, I the spec says
+/-6%, but it even worst now, following the change from 240V to 230V.
Noothing actually changed for most people - the tolerance has just been
increased, and is not symmetical. But I've measured as low at 185V here
on occasions. It really does vary here a lot.
50mV below the minimum on your heater is probably nothing to worry
about, but if the line voltage sags further, then it might be more of an
issue. If the line voltage drops 5% one day, then it will drop a further
350mV on a 7V heater. So then its 400mV low.
I'd personally be tempted to get it 'right' for a typical mains voltage
to give youself a bit of room for when the line voltage changes a bit.
>There is a 208 volt tap on the filament xformer but I would have to put in a
>dropping resistor in the primary to bring the voltage down to 7.5 volts.
>
The resistor would also reduce the inrush current, which might not be
such a bad thing.
>Is it worth the effort? Am I hurting the tube with the lower filament voltage
>or am I extending the life?
>
I'm no expert, but I would be concerned if is is 50mV below the minimum
voltage on a 'typical' day, since any line voltage will always vary a
bit, suggesting it is likely to go even lower on a 'low' day. However,
if the lowest it ever goes is 50mV below the spec, then I'd not worry
myself about it.
To be honest, making one measurment (and quoting it to 10mV) on one day
is not really that much use. You really need to do this several times to
find the minimum, maximum and typical values, then decide what to do.
--
Dr. David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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