>
>I know there was a thread about this a bit ago........But.......
>
>
>The arcing that I am having is in the front wafer of the switch. This wafer
>just switches the tuning cap padder for 160 meters.
This usually indicates a stability problem or spilt coffee. .If you have
a dipper, it might be fun to look for resonances between 150 and 160 MHz
in the lead to the open switch.
>
>The cap is 170 Pf. The open contacts arc when in the 80 meter position. I am
>not sure if it is a parasitic or not. I would say not.
>
>Rich's special plate suppresser is installed in the plate lead. The gap
>that arcs is almost 3/4 inches wide! Why does the tune cap itself arc ?
>
3/4 inch is an incredible air gap, Jim. This feat should take more than
4x the anode supply potential. To find out if it's a vhf parasitic, try
increasing the inductance in L-supp. in order to decrease VHF-Q in the
anode resonant circuit. / One method of reducing feedback is VHF
cathode loading. We use this in our 3CX1200A7 suppressor retrofit kit
due to its extraordinarily high feedback C. . For starters, connect
25pF to 36Pf in series with a 10-ohm MOF resistor. The R and C should
have low intrinsic L. . (we use a Matsushita resistor. ). Use short
leads and a new ground lug at the site if it will reduce L. The RC combo
goes from one or both filament pins to ground.
>Did Ameritron re-design this portion of the switch ?
doubtful. / The stock bandswitch tests at over 5000v on a high-pot.
The peak RF potential in the amp. is about 2100v less. The bandswitch
should not arc.
Photos of AL80 bandswitches are on my Web site. See Figure 15.
>
>I really do not want to replace an $ 80.00 switch. Let alone the fuss of
>replacing it.
>
cheers, Jim
- Rich..., 805.386.3734, www.vcnet.com/measures.
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