Plate Spacing

[KA0KUY]

What is the plate spacing for 'brewed variable caps in a 100W tuner.

Thanks
John, KA0KUY

[VU2NAN]

What is the plate spacing for 'brewed variable caps in a 100W tuner.ThanksJohn, KA0KUY

Hi OM John,Here's the link to an article you may find useful.http://users.tpg.com.au/users/ldbutl...Ant_Tuning.htm 73 Nandu.

[K7MEM]

John,

My 5BTV and MFJ tuner just had a run in with a lightening storm. It blew the 75/80 Meter resonator to bits, welded all the plates in the tuner's capacitor together, and melted the tuners inner wiring. I was able to reuse the cores and hardware. The tuner was a MFJ 16010ST, but MFJ says it is equivalent to their 901B. Anyway, the tuning capacitors inside are what I consider "receiving variables". They have a lot of plates and they are very close together. Yet MFJ rates the tuner at 200 Watts.

I used that tuner with my Icom IC-735 without any real issues. The problem that I ran into is obtaining initial settings on the tuner. Once the tuner is set correctly, it works just fine. However, there are some settings that can cause very high voltages across the capacitors. So tuning up with full power can cause the plates to arc. I solve that problem by always presetting the tuner with my MFJ-259, and always pre-tuning my transmitters into a dummy load.

I rebuilt the tuner, but I used capacitors that I consider "transmitting variables". They are physically bigger and have a much wider plate spacing. Here is a link to a picture of the types of variables I used. http://www.seboldt.net/k0jd/lil-spc.jpg . The ones I used are like the single variable in the picture. Granted, they won't handle 500 to 1000 watts, but they will do the job for transmitters under 200 watts. The rebuilt tuner seems to work good but the antenna is now a 4BTV. I will try and rebuild the 75/80 Meter resonator when I get the chance.

Martin - K7MEM