[TenTec] Omni VI & Titan tuning repeatability

[Dave Bowker]

The major cause of the Titan I power output and tuning drift problem is due to dielectric heating of the plate circuit DC blocking capacitors.  Ten Tec uses two 0.001 uF/6 kV disc ceramic capacitors with a Z5U dielectric characteristic in parallel (C6 and C7) for this application.

Type Z5U disc ceramic capacitors exhibit poor RF current and temperature performance (especially at the lower frequencies), and a very small change in temperature due to dielectric heating causes a significant change in capacitance, varying  as much as +20%  between the temperature range of  +20C to +35C (capacitance can actually vary as much as 45% over the temperature range of +10C to +35C).  Such a change affects the Titan I tank circuit tuning capacitor (C26/C14) setting significantly as the temperature of the blocking capacitor changes with operating time.

Replacing the two disc ceramics with 0.001/5kV Type 858 doorknob capacitors having an X5V dielectric characteristic and rated for RF current handling applications eliminates the drift problem.  

I'll be happy to email temp. vs dielectric curves for the subject caps, mod instructions, and photos to anyone requesting.

73, Dave, K1FK
Fort Kent, ME