Hi again,
Powered up the amp .. filaments light .. blower works .. timer circuits for
HV and Blower work.
Having trouble tuning it ..
Vacuum caps for plate and loading.
Have loading cap at minimum. Evidenced by the plates in the vacuum cap moving
away from each other.
Band switch on proper band ( assuming a lot there in the design as it is home
brew )
I only get a very small dip in plate current .. maybe a 30 - 50 ma dip.
And the tuning / dip is SLOW .. have to tune the cap a lot to get that .. not
like a regular variable cap.
Typical for a vacuum variable cap ??
only about 400 MA at dip .. and with that only 400 Watts output.
Calculations would indicate about 800 Watts at 60 % .
The tubes do get a bit red .. and I guess under normal operation
that is normal so long as the max plate dissipation isn't exceeded?
How rugged are 4-400A's ?
Now .. if I , while on 40 meters on the rig, leave the amp on 80 meters.
The tuning cap is all the way to one end .. minimum capacitance ..
which I guess makes sense .. the amp puts out the same 350 - 400 watts with
only
200 ma of plate current
and minimal drive .. calculations at 200 MA , 3500 VDC plate, and 60%
efficiency, is about 408 watts ..
Which would seem to be in the ballpark.
Is there a preferred tuning method for this type of amp ?? I don't want to fry
the tubes and am so afraid I am going to do that..
I should use my keyer I guess and get a 50% duty cycle ...
Question about grid current ..
ok .. the spec is like 35 ma for 2 tube .. the grid current meter is (
appearance of meter )
0 - 0.5A .. so I assume its just the meter used and its probably 0 - 50 MA
instead of 0 - 500 ma.
UNLESS , because its a grounded grid amp and the screen grid and control grid
being grounded there is
more current being metered for " grid current " ??
I will have to add the RF CHOKE, and thanks for the replies
If I turn those vacuum caps past the stop ... and it still turns , ( slips ) ..
is that going to hurt them ?
Seems tough to write down any kind of repeatable tuning settings .. when they
can slip like that ..
Is the tension / stops adjustable?
What would be the approximate drive power for an amp like this ?? 70 - 80 watts
at most adjusted as to not exceed the grid current?
I can send pictures and a schematic to anyone that might want to help me figure
things out.
I also heard that 3 - 500Z 's are drop in replacements .. is that true? I can
look it up .. just wondering .
thanks in advance for any and all help ..
Randy - N2CUA
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