The AM Forum

The 813 rig I have calls for a Cardwell PL7006 capacitor in the output circuit. Does anyone have the specs for it? Natualy it is missing from the rig.

The schematic indicates it is a 365 PF variable but does not indicate the voltage rating.

Does anyone have the specs, or even better an equivalent cap they want to sell?

Assuming plate modulation, what is the voltage you are running on the plate of the final? Double it for 100% modulated plate voltage, and then add 35% to 50% more as a safety margin, to determine safe working voltage rating.  For low level modulation, don't double the plate voltage.

A 0.175" spaced capacitor (7000 volts rating) always worked well for me @ 2000 volts plate modulated, but it would sometimes arc over @ 2500 volts plate modulated.

fwiw the Cardwell C90-0001-000 (stamped on back) is 200pf, 0.175 spacing in my dual 813 rig under construction. I plan to band-switch a couple of 100pf/ 5kv  N750 doorknobs to it on 160.  Think they'll be ok if SWR's not too high. Not sure where your PL7006 nomenclature came from.

Pi net constants for AM mode that I'm building, where R(tubes) = Ep/(k*Ip) are:
k = 2 for AM , Ep =2000, R(t) = about 2800 ohms.

For Q = 12 and Z out = 52; C, tune is air variable.
Coil stock is 2.5" dia. Airdux, 6tpi, 0.778uh/turn, .167 spacing, #12 wire.
                                                               Closest whole
freq.      C,tune(pf)     C,load (pf)     L (uh)       Turns    Stock length (in.)
1.9        325               1781            23.5          31        5.167  (23.9uh actual)
3.8        163                 891            11.6          17        2.883  (11.4)
7.2         86                  470             6.2          11       1.83     (6.4)

I may use 3/8" Cu tubing on 40 so above Airdux lengths will change.

Why don't you post the dimensions that you are working with and us old buzzards will go look in the swill pile to find something that will work.
Keith
WA1HZK