[TenTec] Omni VI & Titan tuning repeatability

[Dr. Gerald N. Johnson, electrical engineer]

The plate blocking capacitors should be the least effect at 160 meters
because the tube plate C is far less than the tuning C. At 10 meters the
tube plate C is a large fraction of the circuit tuning C so changes in
the blocking capacitors may have a greater effect. On the other hand the
tube C is maybe 20 or 30 PF and the 1000 pf series C of the blocking
capacitors can change a lot without changing the effective tuning C. But
the posted complaint was loss of output at 160 meters, not 10 meters.

On the other hand, loading padding capacitors are only in the circuit on
the low bands and drift in their value will change the output of the
amplifier.

Only changing 45% seems small for the Z5U dielectric. I've seen some
loose 80% from room to soldering temperature. Suitable only for
uncritical bypass applications when the bypass capacitor has been
selected to have several times the value needed for stability. NOT
suitable for any kind of tuned circuit.

858s are good, expensive, and hard to find, but good for RF circuits.

73, Jerry, K0CQ

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.