Eimac recommends a # 51-C45 Siemens spark gap between the cathode and grid on a TC-156 to hold internal tube arcs below 4 joules. Any sources for these? Thanks! Phil, K5PC -- FAQ on WWW: http://www.contesting.com/FAQ/amps Submissions: amps@contesting.com Administrative requests: amps-REQUEST@contesting.com Problems: owner-amps@contesting.com