GU-84b based amp ? tetrode boards for control.
OK so, working again on my amp, 2.3kv on plate, 350v (when ON) to G2 and
G1 has -65v. I have well over 1 amp available for plate current if
needed.
Used several tank calculators, Jim Hawkins, PI network v1.0, G4FGQ?s
calculator..whatever
Else I could find out there to do comparisons. Found out that the W4ZT
calculator was pretty close.
I used about 940ohm for my plate impedance, I can run 1, 1.5, 2kw
calculations but I started with 1.8kw. assumed that the tank Q
Was 12 ? 12.5, Rp made 968 ohms.
I set this all up with my Boonton inductance meter, cap meter on the C1
and C2 (all out of circuit) and assembled it. I have done this
Several times. I used my MFJ analyzer and setup the circuit, tube in
place connected just swept the tank and looked OK.
Power up -
3.8mhz,
C1 ? variable to 0 to 500pf, vacuum cap. Set as needed
C2 ? variable to 1000pf vacuum cap PLUS THREE 470pf Russian door knob
caps. 1400- 2400pf total available. (I checked these with cap meter all
ok)
Set that as needed.
Inductance pretty close to 5uh a little below, I had to short one coil
section to get it there as I am using the whole coil I wound
Out of ¼ copper tube ? wound over a Krylon spray can.
Now then?
Problem I am CONSTANTLY having is to have tons of C2, like the vacuum
cap has no more, seems like both 80m (and 40m
I tapped the coil there for 40 also). I can pull easily 1.5kw out on
both these bands but its with the vacuum cap out all the way (max
capacitance) and
When I am turning the cap in (decrease pf) the power decreases. And I do
see the grid current start to drop also.
I switched from a 600pf to 1000pf vacuum cap to see what that would do
and it still wanted more. I have checked the total C2 pf readings they
look OK.
What?s wrong with this picture??
Now what direction should I go in here with this? Assume different Rp
and see what I can poke and hope with?
Thanks ?Chuck ~ka1mwp
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