by 5B4AIY » 23 Aug 2013 07:43
Hi, Villi,
I obtained some of my capacitors from eBay suppliers, and they were relatively inexpensive, and the postage was free! These were from a supplier in Hong Kong. I have also obtained similar components from RS Components. Although they are a UK company, they do supply world-wide, and here in Cyprus I have had excellent service from them. Then there is Farnell Components, and they also supply world-wide. Unfortunately, unlike RS Components, Farnell imposes a 20 UK Pound (About 32 Euro) minimum charge. I have also dealt with mouser.com and they too will send world-wide.
I would recommend silver mica capacitors, with a working voltage of 500V. The amplifier is easily capable of 150W and the peak to peak RF voltage can be as high as 250V when working into a matched 50 ohm load. If the load impedance is higher, then naturally the p-p RF voltage will also be higher. The 500VWKG capacitors easily fit on the PC board without a problem.
You should at least consider replacing C27 in the 10m filter, but use two 100pf capacitors instead of a single 220pf. Similarly, if you are going the whole way, then replace C24/C21/C18/C15/C12 with a pair of capacitors instead of a single component. In my case I only detected excessive dissipation with C27, and have not had any trouble (yet) with any of the other capacitors, but I do have silva mica repacements available, just in case.
73, Adrian, 5B4AIY