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Reviews Categories | Amplifiers: RF Power - HF & HF+6M | AMP SUPPLY CO. LK-500 NTB Help

Reviews Summary for AMP SUPPLY CO. LK-500 NTB
AMP SUPPLY CO. LK-500 NTB Reviews: 6 Average rating: 3.5/5 MSRP: $1,595 in 1988
Description: Legal limit no tune version uses 2 3-500z tubes.
Product is not in production.
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K7BIT Rating: 2/5 Jun 16, 2019 19:53 Send this review to a friend
OMG WHAT WAS AS Thinking  Time owned: more than 12 months
So I have done several versions of Lk500 series, ZA/ZB/ZC all good amps, however NTB total pile of shit. Not effective at no tune, final just broke down and rebuilt as ZB, now it works perfect. Be aware schematics are horrible. And many units don't have the board they claim or are missing circuits on the schematics. (QSK board good example.)
But once you built to ZA or ZB spec you end up with good amp. It is not a beginners amp however, you need to add multiple protection elements, tune input network to rig. K7BIT
KF4DSG Rating: 3/5 Apr 16, 2012 14:05 Send this review to a friend
Good amp but has its limitations  Time owned: 6 to 12 months
I also have owned 500 model and worked somewhat ok not to be compared to a henry of course but ok, also NS1R you are aware billy passed( Omega Electronics)
NS1R Rating: 4/5 Jan 18, 2011 07:35 Send this review to a friend
good is price is right  Time owned: more than 12 months
I owned the single and dual tube versions of this amplifier. I also have experience with the no tune version. The No tune version is a sacrafice of less efficency but not having to tune the amp. The tuneable models give more power out for power in. If you look inside you can adjust the input /output torroids and get more power out (efficency). This requires squeezing the wires around the torroids. Be careful as there is high voltage and it could kill you. The former service manager from Amp Supply had a repair shop in the carolinas called Omega repair. I really like my Amps but moved into a Condo and had to sell them.
K4LD Rating: 3/5 Jan 18, 2011 05:56 Send this review to a friend
Great idea, but has drawbacks  Time owned: 6 to 12 months
Let me start off by saying that I love the idea of this amplifier. What's not to love about an instant band switching, instant on (3-500Z's), legal limit (or near it on CW) amplifier?
I restored mine, after picking it up with some issues. The previous owner hadn't paid attention to the SWR on his antennas, and commensurate damage had taken place. Be advised, if you find one of these units with issues, Amp Supply was famous for not documenting changes in their schematics. The amplifier itself is totally different from anything documented on paper. As a result, I ended up taking my unit to K4ICL, as he is one of the only people who repairs these amplifiers, and knows what he is doing.
The amplifier is VERY sensitive to SWR. Anything above a 1:5 SWR, and you have problems. This makes me very nervous, because I don't own a high power antenna tuner. All my antennas consist of resonate wires, but I'm very careful to check all of my antennas SWR's before I ever turn the amplifier on.
All in all, it's an OK amplifier. Finding owners or people who have them is rather difficult, and finding people who can repair them will be next to impossible in the coming years. This would make a good amplifier for a contester on a budget. I myself am not "in love" with the amplifier, and might eventually sell it. For now though, it does the job and performs well.
KE4EX Rating: 5/5 Nov 18, 2005 21:44 Send this review to a friend
Find One - Grab It.....  Time owned: 3 to 6 months
Okay it's mid 1980's equipment.
Great set of glowing jugs can not be beat.
# 4 # $4$ Great :>)
Had mine for several months, love it.
I change bands and talk.....
Drive her with a 1000 MP Field 90 watts on 75 meters 900 to 1400 on peaks.
Quiet as a church house mouse.
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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