<html><head></head><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px"><div dir="ltr" id="yui_3_16_0_1_1447871009029_4489">I have several amplifiers that use two 3-500ZG tubes as amplifiers. Based on my 57 years of hamming, I have noticed most are very similar and mostly knock Offs of the SB220 series.</div><div id="yui_3_16_0_1_1447871009029_4838" dir="ltr">B. C. tubes (before China tubes) my SB 220 used Eimac tubes which would last 0 years in Amateur service, if not abused. My SB 220 would do 1100 to 1200 watts out with 75 or so watts of drive and 700 to 750 watts with one (1) Eimac 3-500Z (non ZG). Less power out per tube was due to power supply constraints, thus three fourths as much power out with one tube as with two tubes.</div><div id="yui_3_16_0_1_1447871009029_4839" dir="ltr"><br></div><div id="yui_3_16_0_1_1447871009029_4840" dir="ltr">NOW A. C. (after China tubes) I only get 750 to 800 watts from two china made tubes in my SB 220 with APPROX 3,000 VDC. on the plates of the China tubes measured with a Fluke meter and Fluke HV probe. That is with 75 watts of carrier from my Ten Tec Omni VI transceiver.</div><div id="yui_3_16_0_1_1447871009029_4922" dir="ltr"><br></div><div id="yui_3_16_0_1_1447871009029_4945" dir="ltr">However using same China tubes (different pair but same age and use), in my Amp Supply LK 500 ZA, I get at least 100 to 1200 watts out wit same drive from same transceiver.</div><div id="yui_3_16_0_1_1447871009029_4979" dir="ltr"><br></div><div dir="ltr">The SB 220 acts like it has one tube and the Amp Supply acts like two tubes as far asp power output is concerned.</div><div dir="ltr"><br></div><div dir="ltr">I bought eight 3-500ZG tubes at the same time from the same seller and of the same brand. One of the eight shorted after only slight use. I am puzzled about the disparity between the two amps using tubes of same age and origin. Anyone had this experience with the SB 220 and China tubes. I MISS EIMAC SO MUCH !!!!!! Your input will be appreciated. 73, John, K5PGW<br></div></div></body></html>