|My first QRO amp, and I think it was a wise choice!
||Time Owned: 6 to 12 months.
|LK500ZC...I have had more fun with this amp at home, on the road and in a few places only insane people would even try to use a transmitter. I called the owner, went over, and he had the chassis apart, and was working on a Ten Tec Titan, and some old EF Johnson amps. I had previously looked at some Ameritrons in Colorado for $1200, and the newer ones had that cheap MFJ feel to them, plus the owners thought it was something really special. I looked at Alphas outside Denver. $$$$$$$$$! WOW! Cool stuff, but not with my income. I looked at some nice old Dentrons, but 8875s?? Yeah, great! If those 8875s ever go bad, I am probably SOL. Then the LK500ZC came up for a grand. Little to no tuning, easy to use, and the Chinese are making okayish tubes for it. This one had the SLC Utah Varian era Eimac mid 1980s (Late 1984 & early 1985) tubes in it. Not my first choice for a 3-500Z, but certainly not my last choice either. The Salt Lake City tubes did have some seal problems. I resoldered the pins with a clean DC resistance soldering rig, and that horrid silver solder jewelers despise, because the solder's melting temp goes up after the flux goes away. Silver or gold jewelry would melt before the solder ever does, so I doubt even RTTY or AM will run the solder out of that pair now. I made a dummy load from some Aryton Perry wound resistors, and a small value variable cap, in case there is any inductance in the no/low inductance resistors and bathed the whole array of resistors in a 10 liter bucket of oil. I bought a really nice old Heathkit 2060A antenna tuner, and am loving life, for now. I got a real speaker & made a preamp, EQ & noise filter (redundant) for my Yeasu FT-857D so it does not sound like a tinny tiny total cheapo crap speaker. I just found an old HW 101 Heathkit including PSU, preselector Q multiplier, & SWR Power meter, and now I can go all vacuum tubes. I made quick work of fixing up the HW101. I also just bought two 6200 volt CT plate transformers for $100, so I am starting to design a couple home brew amps now. With the LK500 ZC I am in no hurry! I just fixed up my late father's Chevy Blazer to run the linear amp mobile, by moving the spare tire to a rack, and making a box for deep cycle batteries and a big charger inverter for a sail boat. I have a generator mounted on the tire rack, and got a 225 amp alternator. That Amp supply is built tough enough to have made it to some pretty remote places, over some horrific roads. I put up a kite antenna, and put a resistor in series with a ground to a replica of an old livestock bridge over the Verde River and made some contacts from a very deep canyon. GPS even stops working in that canyon. I just wanted to see if and how that would work, and it does! The weather turned sour really fast, and I had to tie off the kite, cut the wire from the tuner and just get far far away from it, or risk a lighting strike. I do pull the tubes, for transport and I reinforced the Peter Dahl transformer mounts. This amp is built like a steel mill ball now. It was pretty rugged to begin with. They really are super little linear RF amps! My newfound plate supply transformers weigh in at over 50 Kilos each. You won't see me taking those anywhere, unless I am using a hand truck or a truck with a lift gate. I realize the LK500ZC was probably made when I was in high school, and there are newer better amps now, but I am still playing through the 1973 Fender Vibrolux Reverb & 1977 Les Paul Kahler Brass Works NAMM demonstrator guitar I bought with my paper route money. Some products are just worth keeping, and the LK500ZC is on of them, for me anyway. I played a lot of guitars and amps before I made that purchase too. 1000s! My uncle owned a music store, so.... I think I have a nice amp, despite it's few shortcomings. I can't wait to see what I can do with 0-4000 volts DC plate supply!! Double it, if a hook those up in series. I repair audio amps, guitars, guitar amps, test equipment, hi fis, TVs & RF stuff. I have the LK500 now so, no hurries no worries. With it and the SA 2060A antenna tuner, I am setup for now. |
Earlier 5-star review posted by KI7AQJ on 2016-08-22
Okay, so the solder tried to melt out of the Varian era Salt Lake City tubes, so I took a filament transformer, and made a resistance soldering rig. I removed & cleaned the base & pins, then used high melting temp silver solder to resolder the pins back on the 3-500Zs and added a fan. I bought a NOS Exide charger inverter, moved the spare tire from under the truck to a rack on the back of the truck, and put a box with 4 deep cycle batteries and the inverter charger where the tire used to be. Now my LK-500ZC has been taken to some stupid remote areas over roads that are easily confused with the creeks and washes they transit. This amp is run out the back of the truck on a dedicated 25 amp 120 volt circuit, mobile, and run off the dryer outlet at 240 volts at home. So far, it never fails to deliver the goods. I had it in a very deep steep canyon, and used a kite antenna to get out on 40 meters. I really enjoy having this linear, a Tarheel, and a dipole set up at home with an SA2060 Heathkit antenna tuner. As they say, "I am in the big-time now." I drive it with a Yeasu 857D or 897D, which can be used at home or on the road. I picked up a Heathkit HW101 and have pushed that transciever up the the legal limit, and gone 100% vacuum tubes. If the SWR is not right, the amp folds back on itself, and no harm, no foul, no expensive damage. Usually I check everything with an analyzer first anyway. I can cut the SA2060A out & use an old Viking Matchbox into an LCR switched through a solid state home brew, and match the impedance, inductance & capacitance of both tuners, & go. I will have a 2KW dummy load soon enough. None of that MFJ load in a tin can stuff either. Yeee-uck! I wish my yard was larger and not so close to the power lines, so I could have a nicer antenna set up. I hope to move soon, so I am not going nuts erecting towers. 73s KI7AQJ
|Amp Supply repairs
||Time Owned: more than 12 months.
|I just got finished with a total refurb of my LK-500ZC and used Al K4ICL for some advice and repair info. See him at www.k4icl.com . He is the new "go to" guy on all Amp Supply amplifiers and has taken over for Bill after his passing. Friendly and informative on the phone, he seems to know what he is doing. If I didn't do the work myself, I would definately trust this guy for my amp work! I added a step start, HV current limit resistor, HV glitch resistor, new AG6K type parasitic suppressors, replaced all HV electrolytics, all new equalizing/bleeder resistors with new type MOF (Metal Oxide Film, do not use carbon!). My old carbon resistors had two that had more than doubled in value and one was open. I replaced the HV wire from the ps board to the bottom of the plate choke, I didn't like the thin insulation of the original. I remounted the DC block to use more nichrome wire between it and the plate choke. Also remounted the VOX/QSK switch to the front panel right above the H/L air switch. I always hated having to reach around to the back to switch from standard semi break-in to full QSK. I raised the fan slow-down resistor as it was burning the circuit board because it was mounted right on top of it and there was no space for airflow. One other thing I might mention is that I removed 2 extra In parallel) resistors in the Grid Shunt because they did not appear in the scematic. I returned it to what the manual says. When I did that, the grid meter barely moves with full drive and even if I mistune the load control to be "light" (MORE capacitance) loading, which should bring up the grid current quite a bit. Putting those resistors back should make the meter operate properly in the grid position as it did before. I really enjoyed this project and will keep this amp for a while. On 160M the output with about 90-100 watts drive is about 1100 watts, 80-40-20-15M is about 1200-1400 watts, 17M and 12M WARC are still over 1KW as is 10M. Trust my measurements as they were performed into a special Radiodan modified multi-range Bird 43 into a 50 ohm dummy load. Multi-range 43 Wattmeter calibrated with a Bird 6091 calorimeter. I like this amp as it is quiet in the low speed air mode and is very stable with these mods. 73, Dan W7RF|