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na9d@mindspring.com: wrote
> Why do you need a good bandswitch to prevent arcing at high voltages?
>
>
Jon,
With higher HT at the anode you get a higher ouput impedance RL, therefore
the resulting RF voltage over the tank.circuit, no DC as it is blocked, gets
higher at the same output and even higher if you make use of the better gain
which results in more output at a given drive.
Your tank-circuit needs less L and it becomes very likely that shorted
turns
act as tesla coils causing arcs through the bandswitch if distances between
contacts are not wide enough.
So far I have no experience with the 4-1000 which is comparable
to the QB5/1750 which I use in a couple of homebrew amps.
But I have used both, QB4/1100 and 4-400, in my modified L-4B.
There was no difference in gain with both types ( 12-13db ) at 4KV, so
probably the 4-1000 being in the same family, will amplify likewise with
anode voltages between 4.5 and 5KV.
Measurement equipment here are Bird and R&S wattmeters + scope .
73, Peter
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<BR>
<BR>
<BR>na9d@mindspring.com: wrote
<BR>
<BR>
<BR><BLOCKQUOTE TYPE=CITE style="BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT:
5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">Why do you need a good bandswitch to
prevent arcing at high voltages?
<BR>
<BR></BLOCKQUOTE></FONT><FONT COLOR="#000000" SIZE=3 FAMILY="SANSSERIF"
FACE="Arial" LANG="2">
<BR>Jon,
<BR>
<BR>With higher HT at the anode you get a higher ouput impedance RL, therefore
<BR>the resulting RF voltage over the tank.circuit, no DC as it is blocked,
gets
<BR>higher at the same output and even higher if you make use of the better
gain
<BR>which results in more output at a given drive.
<BR>Your tank-circuit needs less L and it becomes very likely that
shorted
<BR>turns
<BR>act as tesla coils causing arcs through the bandswitch if distances between
<BR>contacts are not wide enough.
<BR>
<BR>So far I have no experience with the 4-1000 which is comparable
<BR>to the QB5/1750 which I use in a couple of homebrew amps.
<BR>But I have used both, QB4/1100 and 4-400, in my modified L-4B.
<BR>There was no difference in gain with both types ( 12-13db ) at 4KV, so
<BR>probably the 4-1000 being in the same family, will amplify likewise with
<BR>anode voltages between 4.5 and 5KV.
<BR>
<BR>Measurement equipment here are Bird and R&S wattmeters + scope .
<BR>
<BR>73, Peter
<BR>
<BR>
<BR>
<BR>
<BR>
<BR></FONT></HTML>
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