Amp Supply Company LK 500-ZB

[KF7MJF]

I just purchased an LK 500-ZB from the estate of an SK. This is my first amp, and from what I can tell online, it's a pretty solid unit. Right now it's wired for 220, and I have to get inside and switch it to 110, which I'm told is a pretty straightforward process.

So while I've heard a lot of good things about these units, is there anything I should be aware of, as I'm setting it up and using it?

[W9GB]

Stephen -

Tom, W8JI has basic HF amplifier usage / operation DOs and DON'ts on his web iste.
http://www.w8ji.com/Amplifiers.htm

Bill Edwards, K4BWC(sk) who passed away in 2008 provided service (Omega Electronics) for this Amp Supply model.
http://www.omega-electronics.com/

Al Link, K4ICL currently provides service for the Amp Supply HF amplifiers
http://www.k4icl.com/

Due to the age of these units (> 30 years), perform regular maintenance (clean the inside)/remove dust
and perform a close visual inspection for bulged or burnt components.

Some radio amateurs (DX contesters, daily amplifier usage) will update the HV section (change/replace electrolytic capacitors).

w9gb

[AC0H]

Do not switch that amp to 120V!
You are in the big leagues now.
If you can't swing a dedicated 240V line to run an amp then sell it and get one that will run well on 120V like an AL-811 or such.

[WB2WIK]

I'd be really careful running that amp on 120V. At full power it will draw about 22A from a 120V circuit, and most household circuits are 15A.

If you run it on 120V, I'd suggest either a dedicated 20A circuit (12 AWG wire and a 20A breaker, with a 20A outlet) or never trying to drive it to full power.

[K7MH]

In general from what I have read about that amplifier, it is held in pretty high regard.

I found a lot of interesting commentary about it in the eham reviews of it.
Some of the reviews shared what they thought was good about the amp and also the shortcomings they found.
Worth a read I think.
http://www.eham.net/reviews/detail/1084

[WB2WIK]

In general from what I have read about that amplifier, it is held in pretty high regard.

I found a lot of interesting commentary about it in the eham reviews of it.
Some of the reviews shared what they thought was good about the amp and also the shortcomings they found.
Worth a read I think.
http://www.eham.net/reviews/detail/1084

It is a nice amp, I actually had one for a while about 30 years ago. Although the bandswitch was labeled "AUX" and not 10 meters, the amp worked fine on 10 meters (and probably 12m too, although I'm not even sure we had the 12m band available to us at the time).

Amp Supply made lots of changes, though, and some were "improvements" while some probably weren't. I know the internal parts used in the amp I had didn't match the schematic or parts list in many areas, indicating what I'd call "undocumented changes."

Some reported filament pin overheating with this amp due to lack of adequate base cooling. Whether that's really a problem or not likely depends on exactly how the particular amp was built. If the pins get so hot the solder melts, that can also harden the socket contacts and make them unreliable.

Probably any issues are caused by hard service such as RTTY or AM, or using the amp very hard on CW. With normal SSB duty cycles, the tubes don't get all that hot.

[WA7PRC]

I echo the comments about 240 vs 120V. The manual recommends either 240V or a dedicated 120V/30A circuit. If you're going to do that, you might as well go with 240V and halve the voltage drop in the wiring.

Steve/WB2WIK mentioned concern about cooling. 3-500Zs don't like to be be without cooling, especially on the filament pins. I learned the hard way that insufficient cooling can ruin your day. The LK500 uses a cooling scheme similar my Heath SB-220. They blow air across the tube envelopes, with the fan blade partially below chassis level to move air across the filament pins. It appears they use the same Johnson #122-275-001 (or similar) sockets:



This is what loss of cooling did to the sockets on my SB-220:

A good grid contact is on the left, the cooked filament contact is on the right. You can see that the contacts on the right don't quite close, indicating the spring tensioner got hot and relaxed. Some might've just retensioned it but the sockets were cheap enough to replace (compared to the tubes).

[KF7MJF]

Do not switch that amp to 120V!
You are in the big leagues now.
If you can't swing a dedicated 240V line to run an amp then sell it and get one that will run well on 120V like an AL-811 or such.

I live on my sailboat. I'd have to *make* a dedicated 240v line on the boat.

[KF7MJF]

Thanks for the info guys. As far as the wiring goes, I'm on a 30amp 110v shore power for the boat. So not sure yet what I'll do, I'd hate to bring a second line in just for the radio (FT 107) and amp. I'll figure something out. Right now my tuner, feedline and antenna all max out at 300 watts, so I'm not in an all fired hurry I guess to push legal limit LOL.

[WB2WIK]

Thanks for the info guys. As far as the wiring goes, I'm on a 30amp 110v shore power for the boat. So not sure yet what I'll do, I'd hate to bring a second line in just for the radio (FT 107) and amp. I'll figure something out. Right now my tuner, feedline and antenna all max out at 300 watts, so I'm not in an all fired hurry I guess to push legal limit LOL.

The amp will use almost all of that available line power, by itself. I guess the "give it a try and see what happens" approach is probably best.