Amplifier Tech & rebuild
Amp Supply LK-500 NTC
Tubes: 2 x 3-500Z Eimac
1100 W CW/SSTV/RTTY/PSK31 and 1500 W SSB PEP
Broad band and no tune amplifier
Reviews: 1 Average rating: 4.0/5 MSRP: $(missing—add MSRP)
Description: Legal limit no tune version uses 2 3-500z tubes.
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You can write your own review of the AMP SUPPLY CO. LK-500 NTB.
K1DX Rating: 4/5 Jun 8, 2003 23:36 Send this review to a friend
A good near legal-limit HF amplifier, but within certain limits Time owned: 0 to 3 months
The LK-500NTB is an interesting amplifier. It seems to be very well built and likely to be very reliable. When driven by a 100W exciter (my Icom 756 Pro II), the legal limit cannot be attained; but the manufacturer does not claim full legal power at that drive based on some key specifications stated in the LK-500NT Owner's Manual:
- Power Output: 1100W CW, RTTY, SSTV; 1500W PEP SSB.
- Drive Power: Nominal 80-110W carrier, 100-150W PEP for rated output.
- Load VSWR should be 1.5:1 or lower for no-tune-up factory settings. (50 ohm unbalanced load.)
As you can see, the 1500W PEP is not likely attainable since the ‘Pro II puts out 100W max. or PEP. However, based on my observations, my LK-500NTB is working within manufacturer specifications.
I am not sure what the difference is between the LK-500NT and NTB versions; I have the latter. There is also an LK-550NT that has three 3-500Z tubes in the final, instead of the two in the –500 versions.
As received, my used amplifier had a damaged bandswitch. It appears that a screwdriver may have been dropped into the switch, badly bending a wiper back onto itself. I very carefully straightened it and tensioned it and it appears to work properly and reliably now. The bandswitch sometimes arcs on 20M with a 2:1 (or higher) VSWR; but that’s outside of the specified limits. My amplifier has the 10M circuitry connected for the AUX bandswitch position.
Negative Comments? The amplifier appears to function as specified at the frequency of the factory setting. However, if the VSWR exceeds 1.5:1, an external tuner will be required, and that defeats the no-tune advantage. The Owner’s Manual is plain and terse, but informative. It does include a schematic but no alignment instructions. I find that rated power is only at one point in the band (where factory tuned), so you probably should optimize tuning for your favorite part of the band. Finally, the T/R switching is done using an open-frame relay, not a vacuum relay. This amplifier does not cover WARC bands.
If you do choose to tweak the plate or loading capacitors, be very careful as there is 3KV within easy reach willing to elevate you to Silent Key status. Prior to tweaking be sure to disconnect AC power. Then, observe the placement of all components and mark them (or make a drawing) to identify their function (band plate/loading), and carefully plan your task to avoid contacting lethal voltage points (plate circuit and power supply). I plan to make a non-conductive screwdriver blade-like tuning tool by shaping a wooden dowel.
No-tune is accomplished by bandswitching a fixed and variable capacitor pair, one pair for each of six bands. In addition, a fixed and variable capacitor pair are selected for loading on 3.5/3.8 to 21 MHz positions (one pair share the 3.5 and 3.8 positions; 160M has one fixed loading capacitor; 10M (AUX) uses the FINE LOAD variable capacitor only, which is a front panel control. The FINE LOAD control also functions on all bands (not bandswitched).
The amplifier has a very nice tuned input for the 80, 75, 40, 20, 15, and AUX (10M) bands. I find the input VSWR to be well below 1.4:1 (except on 15M, which is likely mis-tuned).
Bottom line: This is a nice, compact, near legal limit amplifier. I am convinced
that once I’ve tweaked this amp that I will see at least 1000W out on
all bands. I currently see 1000W out on 28.4 MHz and 1100W on 7.1 MHz with just
100W drive. So, if you have an antenna system that presents a 1.5:1 or less
VSWR, this amplifier will do well. If you require a matchbox (tuner), you will
do much better avoiding this no-tune amplifier; instead, go for the LK-500ZB
(which I formally owned) which will easily put 1500W into a dummy load with
just 100W drive.
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KC2LCZ Rating: 5/5 Nov 25, 2003 00:47 Send this review to a friend
LK-500ZC Time owned: 6 to 12 months
I'm getting legal+ on all bands excluding WARC. It uses top notch components and is easy to tune. A new amp of this quality utilizing 3-500z tubes will cost close to 3k and may not provide legal limit. I sent the amp down to Bill at Omega Electronics to have a vacuum relay QSK circiut and a step start added. While it was there he also replaced the aging wiring harness and noisey fan bringing the the amp to "like new" condition. The LK-500ZC will normally sell for under $1,000. on the used market. Big bang for the buck! If you can find one grab it, you won't be disappointed.
WO2E Rating: 4/5 Sep 9, 2003 19:02 Send this review to a friend
LK-500ZC Time owned: more than 12 months
I HAVE THE LK-500ZC THE PLATE TRANSFORMER WENT BAD. I SALVAGE A PLATE TRANSFORMER FROM AN AMERITRON AL-1500 AND A SEPARATE ENCLOSURE HAD TO BE BUILD TO ACCOMODATE THE BIGER TRANSFORMER I SET IT UP FOR 120 VAC.I USE THE SAME FILTER CAP BOARD ETC. BUT WHAT A DIFERENCE NOT TO BLOW THE CAPS I USE A VARIAC HOOK TO 120 VAC WITH JUST 105 VOLTS IT GAVE ME ALMOST 3800 PLATE VOLTAGE AND JUST 45 WATTS INPUT IT GAVE ME 1200 WATTS OUT. I DID NOT WENT OVER THESE NUMBERS THE HOUSE CURRENT WITH 120 VAC WAS NOT HAVING IT AND FILTER BOARD ETC WAS NOT SET UP FOR THE EXTRA LOAD. BUT THE LK-500 REALLY KICKS A$$ WITH THIS PLATE TRANSFORMER SET UP FOR 220 VAC. NOW I WOULD NOT BUTCHER A CLEAN LK-500 THAT WAS WORKING 100% ESPECIALLY WHEN ANY MOD WOULD REDUCE ITS VALUE. OVER ALL ITS A GREAT AMP AND EASY TO SERVICE AND SIMPLE CONSTRUCTION AND IT WON'T BREAK YOUR POCKET. I LIKE IT AND STILL USED AFTER 8 YEARS.
W1ES Rating: 4/5 Oct 17, 2002 08:43 Send this review to a friend
Good Amp for Low Bux! Time owned: more than 12 months
Bought mine back in the 1980s and have used it for DXing and contesting all these years. It's built very well and has been a real warhorse!
The shortcomings, some of which have been mentioned here by others, are the QSK circuit (you can't run the amp in standby if it's wired for QSK without an annoying sidetone), high filament voltage (corrected), king-kong band-switch detents(corrected-- removed one of the two ball bearings-- what a difference!)and lack of step-start for the PS. THere is plenty of room inside to do mods, however, and I've done several: extra cooling holes to the outside through a level beneath the deck, voltage-dropping wire to bring fil voltage to 4.75V and AG6K mods to anode & grid circuits.
With a good QSK circuit (which I swear I've been meaning to get around to playing
with for 15 years but haven't) this represents the absolute best bang-for-the
buck out there! Because the brand is an orphan, you can get them for a lot cheaper
than they should be selling for! Frequently, you can get these for less than
an SB-220 and it is a MUCH (I can't stress this enough!) better amplifier that
also does 160m!
W5MG Rating: 5/5 Oct 4, 2002 15:53 Send this review to a friend
Built to last!!! Time owned: 6 to 12 months
I have owned my LK-500ZB for 6 months. This is one of the finest amps I have ever owned. I own an Alpha 78 and an Alpha 76CA. If Alpha had built an amp that ran 2 3-500z tubes they would have built it like this amp. If you have an opportunity to purchase one jump on it. You won't be sorry.
W5MG Rating: 5/5 Oct 4, 2002 15:52 Send this review to a friend
Built to last!!! Time owned: 6 to 12 months
I have owned my LK-55ZB for 6 months. This is one of the finest amps I have ever owned. I own an Alpha 78 and an Alpha 76CA. If Alpha had built an amp that ran 2 3-500z tubes they would have built it like this amp. If you have an opportunity to purchase one jump on it. You won't be sorry.
KG4ENZ Rating: 5/5 Aug 8, 2002 18:20 Send this review to a friend
LK500ZC Time owned: 6 to 12 months
I OWN A LK500ZC MODEL AND I AGREE ITS A RELIABLE TOUGH AS A TANK AMP.IT PRODUCES 1500 WATTS WITH A 100 WATTS OF DRIVE AND I DO LIKE THE ALO PROTECTION CIRCUITRY THAT PROTECTS IT FROM BEING MISTUNED AND CAUSING DAMAGE TO UNIT.IF YOU CAN FIND ONE ,ITS WORTH THE MONEY.KG4ENZ
WO2E Rating: 4/5 Apr 23, 2002 11:23 Send this review to a friend
BLOWS CAPS Time owned: months
i had this amp #2 3-500z for aboy 5 years the only problem that i had is that it has blown the caps a number of times, 120mfd 450vdc #8, i have use a variac with exellent results. this has safe the caps for aboyt 2 years untill i forgot to bring the voltage down from the variac before turn on
and blow those babys again. the problem is just turn on with the inrush power. if anybody out there has better repalcement caps or a better idea on what to do or replace please e-mail me. WO2E@AOL.COM thanks.
W4VD Rating: 5/5 Nov 9, 2001 13:13 Send this review to a friend
Great Amp Time owned: 0 to 3 months
I bought this amp on ebay a few weeks ago and I am very pleased with it. I have the "ZC" model. It has a Kilovac vacuum relay for QSK and works like a dream on VOX, I get right at legal limit output on most bands, and the WARC bands are very acceptable, with 1200-1300 watts out on 12 and 17 meters. The tuned input is excellent, even on the WARC bands. The solid state tranciever likes the LK50ZC very much. The 2 speed fan is handy during heavy duty operation. The 6 to 1 reduction drives on the tune and load control make for a very smooth tune up and the dial scale makes for easy "tune by the numbers" once the settings have been determined and logged. All in all it's a good amplifier for the money and Omega Electronics has the parts and expertise to keep it running long into the future.
W8JJW Rating: 5/5 Oct 4, 2001 11:41 Send this review to a friend
Really Solid Amp Time owned: 6 to 12 months
I bought this amp at Dayton this year..been using it on 160 mostly on a wire and on 17-10M through beams with excellent loading and output. I typically run 1kw with 30-40W input depending on the band. I have the LK-500ZC. Built like a tank.
G4VGO Rating: 5/5 Jul 14, 2001 04:19 Send this review to a friend
Awsome! Time owned: 0 to 3 months
My amp is the LK-550 NTC (No Tune, Three Hole 3-500's) and it is a very good performer. This is the second Amp Supply unit I have tried, the first being the LK-850 with three 3CX800's in it a few years back.
On CW the QSK is smooth and does a great job with my FT1000D. The only problem is minor, a change in the L/C ratio of the 160m band is called for as is a beefier set of caps in the output circuit because the caps will heat up at full power out on that band. However, at legal power over here, it runs STONE COLD on all bands, all day long, 24 hours a day in a contest.
Very good value for money, and I am sure it will be contesting long after I am gone.
If you can buy one, do it, the external Peter Dahl transformer makes a good
foot rest and at 1.2 KW+ on RTTY, a good foot warmer I am sure.
K6EGW Rating: 5/5 Jun 16, 2001 22:03 Send this review to a friend
More than good Time owned: more than 12 months
Instant on. I have beat mine up for many years. Instructions say "tune for maximum smoke." 1.2 KW
output on all bands.
I now listen to the boss and turn down the input. The tubes do not like 100 watts.
QSK. I never use the fan in high position. Same tubes. My God, what more could you ask for. Built like a brick. The instant on gets me on in front of many.
Get one if you can find one. 73's
N2NFG Rating: 5/5 Nov 28, 2000 21:21 Send this review to a friend
SOLID PREFORMER Time owned: more than 12 months
When I bought this amp 8 years ago, it arrived badly damaged from a fall off a UPS truck. (not US, we don't drop things!) After a trip to OMEGA amp repair, it was as good as new and gave excellent service for several more years, until I developed a liking for RTTY. Even keeping it well within the limits of the manufacturer, the solder would melt from the pins of the tubes. (I will admit that this was still under extreme use, RTTY contesting) But now I had the good fortune of living only a short drive from OMEGA, so in the truck it went for a ride to Knightdale, NC. Bill took a good amp and made it even better. For anyone who runs a ZB or ZA, especially for contesting or continuous duty modes, the mods that Bill at OMEGA can do are highly recommended. First, the deck holding the tube sockets is replaced with one with perforations to allow better cooling of the tube pins. Second, a plate is installed between the tubes and tuning circuit to allow more air to flow past the tubes. Third, a beefier fan is installed for even more air flow. Last, a temp. sensitive switch is installed to kick the fan up to high automatically. I don't expect any tube failure for a long, long time:) Other mods worth considering are the QSK board, and step start protection. (the original QSK scheme leaves a lot to be desired) I know that this sort of turned into a review of OMEGA, but these amps are getting kinda old, and there are a lot of them floating around out there. For a very reasonale price, these amps can be retrofitted with features that will turn one into a better two tube 3-500Z than anything currently available new. 73, Bob N2NFG
WA9UEW Rating: 5/5 Nov 28, 2000 18:12 Send this review to a friend
Great Amp Time owned: more than 12 months
Have had the amp for about a year and a half. Been a great performer. Works great on all modes. I use it on AM with a 950sdx, Put out a whale of an AM signal. Very solid amp!!!! Works great on QSK also. Has vacuum relays. Very quiet. Don`t see too many of them for sale. Am really happy with mine.