Variable Plate Cap in 2x 813 Amp. Question

[Carl WA1KPD]

I recently picked upatn HB 2x 813 amp based on the following circuit http://k6jca.blogspot.com/2010/06/am-transmitter-813-style-part-1-pa-deck.html It is based on the One band Killowatt Amplifiers from the ARRL Handbooks in the early 60s's.

You will note that the original construction used a Vacuum variable as the plate cap. I assume this is because it is what the constructor had available. I would like to go to a regular 1/2 turn variable and one large enough to cover 160 with the appropriate coil. (200 PF?)

I cannot find any overwhelming reason to stay with the VV, but wanted to check with the collective wisdom here.
I have also heard taht VVs do not like to be tuned around a lot as they are brittle. Is this true or an old XLYls tale?

Thanks

Carl

[w4bfs]

hi Carl

found this Jennings app note:  http://www.jenningstech.com/technotes/handling.shtml

I have seen vac var caps used in motorized ant tunas.  I don't know if they were specially rated for that application.  I have seen several glass vv that have lost their vacuum, usually due to cracks in the tabulation or evacuation port

it is possible to use a lost vacuum, vacuum cap as a loading cap since the voltages there are not so high

test it with the hi-pot tester, then you will know  

[Carl WA1KPD]

Actually I am looking for a reason to NOT go with a regular variable and I can't see that the VV adds that much. Besides I have two cool buzzardly National dials I want to use and a multi turn vacuum would take that away.
These will go either side of the window to the tubes

[KB5MD]

I run an 813 amp with regular variables and have never had any problems with arcing or otherwise.