This is a bit of maintenance and tweaking on my neglected GU81 Vacuum Tube Tesla Coil. After a conversation with Steve @testedtodestruction and a flamethrower of a capacitor failure, I’ve made a couple of modifications to the set-up. Firstly, all grids have been tied together converting the GU81 into a triode. At first this seems a retrograde step but there is a noticeable improvement to arc length. I guess we are not trying to run the tube in its best noise free and linear area for this rough oscillator.
With the capacitor failure I had to improve the DC supply and fit a more robust filter cap. Having a very compact build for this VTTC it was difficult to make this modification. This pointed me down the route of electrolytic capacitors in the doubler circuit. Two problems here are, you don’t get 2kV electrolytics easily and the ripple and RF noise may overheat them. The capacitor I am currently using is made from 10 x 47uF 450V caps in series giving 4.3uF at 4.5kV. Bleed resistors are in parallel with each capacitor to help balance the voltage across them and discharge them when off. The extra voltage head room isn’t really required and two capacitors could be removed and would be within working range. Future changes would be to increase the overall value of the doubler but keeping the values similar to the original for testing at the moment.
Initial tests are good and the running temperature of the capacitor bank is less than 21C.
CONTENT:
00:00 - Intro
00:08 - Description
02:44 - Circuit overview
03:30 - Upgrade
05:50 - Variac testing
05:55 - Mains testing
06:10 -Outro
14 окт 2024
