[Johnson] Fw: Valiant Low Output

[Glen Zook]

If you are reading 200 mA on the "plate" meter your
actual plate current is only around 165 mA.  The
Valiant reads cathode current, not true plate current.
 Each 6146 pulls about 12 mA screen current which must
be subtracted from the cathode current.  Thus, with
200 mA showing on the meter your actual plate current
is reduced by the screen current.

If you are getting only 600 volts on the plates then
your actual power input is just under 100 watts.  The
power output of 42 watts is low, but not that low
considering that the Valiant is very lightly loaded at
200 mA showing on the "plate" meter.

The 6146 tube is happier at a higher plate voltage and
is usually more efficient at around 750 volts. 

Also, the accuracy of your wattmeter may not be all
that good.  Even the Bird 43 wattmeter has an average
accuracy of +/- 5 percent of the maximum reading which
means +/- 5 watts if you are using a 100 watt "slug",
+/- 25 watts if you are using a 500 watt "slug", etc. 
Most amateur grade wattmeters are more like +/- 10
percent (if that good) and your reading could be even
farther off. 

As an "aside", if you haven't read the article on the
6146 family of tubes that was in Electric Radio a
while back (and has been reprinted in other
publications since then), go to the K9STH website (URL
listed at the end of this message), choose the K9STH
link, then the article is linked part way down the
list of links.

Glen, K9STH


--- BRIAN ROBERTS <k9vky at verizon.net> wrote:

Gents:  I have a Valiant that appears to have very low
output relative to the input power.   With 120 watts
input (200 ma. with around 600 volts HV)  to the PA,
I'm only seeing 42 watts output.  I'd normally expect
to see about 60 watts.  Bias and screen voltages are
all within limits, and the three 6146s have been
swapped with known good tubes.    I thought I was
pretty good at keeping these Vikings cooking, but
apparently not.   Has anyone else seen this situation
or can you offer any suggestions?









Glen, K9STH

Website:  http://k9sth.com


 
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