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Reviews Categories | Amplifiers: RF Power - HF & HF+6M | Amp Supply LK-550 (3 x 3-500Z) Help

Reviews Summary for Amp Supply LK-550 (3 x 3-500Z)
Amp Supply LK-550 (3 x 3-500Z) Reviews: 6 Average rating: 4.8/5 MSRP: $1899.00 +shipping
Description: 2 piece Desktop linear amp using (3)3-500Z tubes. Seperate power supply sets on the floor.
Product is not in production.
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You can write your own review of the Amp Supply LK-550 (3 x 3-500Z).

KB1SF Rating: 5/5 Apr 13, 2017 21:05 Send this review to a friend
Excellent Amplifier!  Time owned: more than 12 months
This amp was given to me by an old friend back in the early 1990s. However, because I had no way to operate it on 220V, it sat in my ham shack closet for nearly ten years. Then, about a couple of years ago, I had a ham friend bring the power up gradually on a Variac and we then found one of the original Eimac tubes was gassy. So, with a new set of 3-500ZGs installed, I now have a virtually new amp that's been chugging along nicely ever since...all for the price of a set of three new tubes! It loafs at the legal limit (key down) with 100w in. I understand the amp will crank out more power with more drive...but why would you want to? Photos of my amp are on my web site at If you find one, buy it. This amp is built like an absolute tank. The power supply (which sits separately) weighs in at nearly 50 lbs! Tubes are rugged and relatively inexpensive. Plus Harbaugh makes a replacement power supply board when (if) the original ever "goes South" on you.
K5YY Rating: 5/5 Oct 8, 2009 16:19 Send this review to a friend
Great amp  Time owned: more than 12 months
Love my LK550-ZC... (1) inexpensive 3-500Z tubes (2) hard to abuse but can put out 1800 without problems in CW/tune mode into dummy load (3) about 3100 volt from my floor PS which has extra fan speed switch if needed (4) my RF deck has a switched higher speed fan position just in case, keeps tube seals cooler with RTTY or long DX calling stints (5) nice looking (6) brute PS components (7) will operate on 18 and 24mc bands using the usual higher band position method (8) efficiency a minimum of 60-62% on all bands and up to 68% with tweaking (9) covers 160m - A keeper for sure and a reasonable price on the used market.
KE0XS Rating: 5/5 Mar 20, 2007 18:09 Send this review to a friend
This Amp Rocks  Time owned: 3 to 6 months
Had the opportunity to purchase one and jumped at the chance. Ran the amp about a month before sending it to Bill at Omega Electronics to be thoroughly updated and worked over. The ALO board was updated and a thermo switch installed to control the fan when things get warm. The door knob cap on 160 meters needed replacing as it wouldn't hold tune.

This amp runs 1500 watts day and night without so much as a groan. I installed 3 matched graphite tubes. Solid construction throughout. When you grab the band switch and hear it snap into place, you'll know why it will never give you any problems.

The heavy Peter Dahl Transformer sitting on the floor is a 67 pound brute.

I've had Ameritron AL80B, Heathkit SB-1000, Alpha 374 and an NCL 2000. Wouldn't trade for any of them. There's nothing like (3) 3-500Z's in the dark!

N7WX Rating: 5/5 Mar 21, 2006 12:53 Send this review to a friend
FIND ONE BUY IT  Time owned: more than 12 months

Very good amp for the price...put new RF Parts (3) 3-500ZG'S in it and it runs 1500 watts key down all day...The 67 lbs Peter Dahl hypersil in its own supply(1.75 AMP CCS) with a very quiet fan sits on the floor and no problem...The RF deck runs fairly cool and if you push it into dummy load well easy do 2500 plus but why ?

Anyway great quiet running Amp all bands 160 through 10 with Warc bands..Very easy to tune by the numbers easy band changing...
G4IFB Rating: 4/5 Jun 30, 2004 13:20 Send this review to a friend
Reliable workhorse  Time owned: more than 12 months
My LK550 doesn't get much use these days but it's a simple matter to flick on the power, wait a few seconds and go QRO: I know it'll work every time.

My TS850 will drive it to about 1200W output (more than enough for the UK 400W licence limit, at the antenna) so it loafs along.

Having said that, I did once blow a set of smoothing capacitors (replaced with a stack of RS Components HV electrolytics) and lost a 3-500z to an internal short (most likely physical damage in my numerous house moves - nothing to do with the amp). I've also replaced the vacuum relay due to wearing out the old one with full break in CW, I guess.

The Automatic Lock Out seems a little sensitive to high SWR on 10m, but I have occasionally driven it into 2:1 SWR on the WARC bands with no ill effects.

All in all, I'm very happy with it. It "does what it says on the tin".
KE4EKW Rating: 5/5 Jul 1, 2002 01:02 Send this review to a friend
Unique Powerhouse!  Time owned: more than 12 months
To my knowledge, the LK-550 was the only commercially available amp utilizing 3 x 3-500Z tubes. It puts out a little less power than it's more powerful sibling the LK-800 (using 3 x 3CX800A7 tubes), however, the amp can not be over driven like the LK-800. I purchased the amp several years ago from an estate, new in the box and have enjoyed using the amp. I did have the amp's circuits updated to the last year produced specs by Billy Edwards at Omega Electronics a few years ago and have only had to replace the grid/volt meter front panel switch. The amp loafs at 1,500 watts out however to use at its full potential it needs to be driven by a 150+ watt transceiver like the Kenwood TS-950SDX (which is what I use), or higher output (200+ watts) Yaseu 1000D, or Icom 775DSP. The amp is compact due to the very heavy HD power supply being seperate and placed on the floor. The standard power supply puts out around 3,300 volts, so a little more power output would be available if the voltage was closer to 3,700-3,800 volts (near the 3.500Z's 4,000 volt maximum). Personally, I prefer the 3-500Z tube over the 3CX800AZ, being less sensitive to abuse or tuning mistakes. I do highly recommend the graphite tubes (Amprex) over the standard Eimacs due to about 100 watts greater output and they withstand heat better. I have experienced very poor luck with the last Eimacs produced due to loss of vacuum from poor quality tube seals. I like the Amprex Graphite over the Eimacs or other imports due to a much thicker glass envelope and they have served me well in several different amps (graphites are any absolute must for the Kenwood TL922A, due to the heat build up in the corner tube). The LK-550 is truely unique and I am surprised more high output amps did not use the 3 x 3-500Z tubes design. The 3-500Z has very good power and the time proven tube is readily available at a reasonable price.

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