Vacuum Capacitor close to cabinet?

[K9FV]

How close can a vacuum capacitor be mounted to the cabinet wall on 6 meters? I know the space required for arc prevention is required, but how does it affect the tuning to have close to cabinet wall? I've checked capacitance with lying close to wall, and moved out a couple of inches. Not much difference in capacitance measurement.

One end will be mounted direct to front panel with front panel VERY good connection to chassis RF deck. The glass envelope is larger than the ends, and with glass touching cabinet would put ends a good 1" from cabinet wall. If there is a 1/4" between glass and wall - would that be ok?

Thanks for all the help and ideas.

73 de Ken H>

[K9FV]

Darn it - I popped this question without thinking today. I asked a VERY similar question a week ago and got a very good answer then. I had the answer given in my notes, but forgot. Is old age an excuse?

Thanks again for all the help.

73 de Ken H>

[WB2WIK]

Just do it. Vacuum caps are very forgiving and if the chassis proximity adds a pF or two, you can probably still tune where you need to.

I mount my tuning caps on the panel (for 6m) but high enough above the chassis that the glass or ceramic of the tuning cap is at least an inch above the chassis, so there's no measurable interaction there at all. I haven't tried this, but I'd guess if the glass envelope of the cap was literally laying on the chassis below it wouldn't make much difference.

[K9FV]

Thanks for the input Steve - as can be told from my posts/questions I'm VERY new at this tube amp building. I'd really like to make it work as well as my solid state amp I built a few yrs back..... and even more important - SAFE!!!

73 de Ken H>

[W8JI]

How close can a vacuum capacitor be mounted to the cabinet wall on 6 meters? I know the space required for arc prevention is required, but how does it affect the tuning to have close to cabinet wall? I've checked capacitance with lying close to wall, and moved out a couple of inches. Not much difference in capacitance measurement.

One end will be mounted direct to front panel with front panel VERY good connection to chassis RF deck. The glass envelope is larger than the ends, and with glass touching cabinet would put ends a good 1" from cabinet wall. If there is a 1/4" between glass and wall - would that be ok?

Thanks for all the help and ideas.

73 de Ken H>

The only way you can measure capacitance in a VHF amplifier is to measure it at VHF. :-)

I think the old answers were good. More important are the lead lengths and path length through the sheet metal. Remember? :-)

[K9FV]

Yep Tom - as I mentioned in my 2nd post, I now remember. Ya'll gave very good detailed answers then, and I wrote them down - last night was one of those times I put "keyboard" in motion before brain.

73 de Ken H>

[W8JI]

We all do that.