Hi everyone. I just aquired two amp supply lk-500 amplifiers. One is a zb and the other is a za model. Ive done a good amount of reading so far from what I can find out about them online and the general concensus is very positive. I feel like its a solid amplifier and looks really well built. I really would like to have a few things answered for me I have questions about though... I hope W1QJ and KM1H chime in, as they come to mind in the reaseach Ive done so far but I know there are others too very knowledgeable that Id love to chime in. 1. Tube pin cooling seems to be a issue with these amps. Apperently there is a mod/new tube socket that solves this issue and Id like to know if I have the stock tube socket or if I have a modified one? And where do I source info on completing this mod if I don't have it done here? 2. Band select switch had two different types used. I believe I have the good swithch as everything looks great and no arcing at the 160m taps but tell me which one I have in case I'm wrong. The swithc I have in both of these amps are the same and they feel pretty awesome with super positive clicks and looks rugged. 3. Does it look like the 10m mod is completed on this za model I have photoed? 4. Can anyone tell me if they see a glitch resistor anywhere on this unit. So far I have read that it should go in line after the supply / B plus. Idk what b plus is though... 5. The za model has a mechanical relay for the ptt/amp keying , but the zb model has a vaccume relay. Should I modify either with a upgraded qsk kit? Leave the zb model alone and add vaccume relays to the za model replacing the mechanical relay? 6. These probably haven't been ran in over a year untill I fired both up just a couple days ago. So far the voltage is 3000 and 3200 volts for both. They both seem to put out about the same power with about 700-900 watts, so I guess the tubes are a little weak. The zb model has plate current that seems a bit high (800-850 ma and 900 is max acording to the manual). I'm driving with 100 watts. Running on a 240v line. I ran a small pile up with the ZA model one evening and the next moring and I got GLOWING REPORTS! It seemed almost every contact was complimenting my signal and a couple guys couldn't get over how great my signal was lol. Ive never got reports like that with my al-1500 putting out legal limit, so idk maybe coincidence or great conditions. Also these things are quiet! Its about half as quiet as the al-1500 and this leads me to believe possibly a aftermarket internal fan was installed as Ive read in a couple places people changing the fans out because they were too noisy on "high". So far i'm only experiencing one fan speed on these units, and the fan installed is a "nidec torin". They also have additional installed fans on the outside of the cover on the transformer side. Thanks for taking your valueable time to help me out here and get some questions answered. I'll provide additional photos if needed.