Amp Supply Company LK 500-ZB

Discussion in 'Amateur Radio Amplifiers' started by KF7MJF, Feb 20, 2011.

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  1. W9GB

    W9GB Ham Member QRZ Page

    Guess you will have to read by candle light or a separate battery based circuit ...
    your transceiver, that amplifier and your basics on that 110 VAC circuit will use all the available current (30 amps) from that shore feed -- when you trasnmit.

  2. KF7MJF

    KF7MJF Ham Member QRZ Page

    Yeah, I am going to see about getting a second line on on the boat, or if I can get into a slip with more juice.
  3. W8JI

    W8JI Ham Member QRZ Page

    If you are on SSB, it won't be so bad.

    First, the LK500 is just barely bigger than something like an AL80B. The cooling is so limited the net safe dissipation in the tubes is only
    700 watts or so. HV also isn't high enough to push the 3-500's to capacity. So you have a 1000-1200 watt PEP amp.

    You might draw 25 amps on a carrier, but average power on SSB will only be a few hundred watts at 1200 watts PEP. Say worse case you have 400 watts average power. The amp will be drawing 10 amps or less short term average from the mains.

    The only place you will run into trouble is on CW or RTTY, or some other high average to peak ratio mode. For example 1000 watts PEP CW power is the same as 1000 watts average power with the key locked closed. In that case draw would be 25 amps or more.

    If you wire for 120 volts (which is really almost always 125 volts) you will be perfectly fine on SSB if you tune with a peak reading meter and a tuning pulser. Just don't run heavy speech processing or push the average power over 400-500 watts out. PEP can be a billion watts, if the short term average power is down around 400 watts out.

    Unless you upgraded the cooling, you would not want to run high average power anyway in that amp.

    73 Tom
  4. KF7MJF

    KF7MJF Ham Member QRZ Page

    Tom, I have read about the cooling problem, I have had thoughts of installing some external cooling to the unit, perhaps one of the systems used on high end PC's to help keep things cool.

    I'm not going to be running CW or RTTY, just SSB, and maybe some AM. Really I wasn't ready to buy an amp, but I got this one with a spare 3-500 tube for $200, so I jumped all over it. Now I've at least got something to study before I put it into service.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    $200 is a great deal...a good tube alone is worth $175, just for the tube. I would have jumped all over that, also.

    I wouldn't run AM with that amp given its evidently weak cooling system and only a limited amount of AC line power available (two strikes). AM is very hard on linear amplifiers. You might run it at 100W carrier power, which is about 6 dB more power than the average HF transceiver can run, but I wouldn't push it beyond that.

    Great deal for $200, though!
  6. W8JI

    W8JI Ham Member QRZ Page

    That amp was actually started as a parts kit. I worked with the designer of that amp at one time. He was personally a great guy, but a real seat-of-the-pants engineer. He never calculated things like dissipation, Q, or anything else. He designed a pair of 3-500's amp for a major radio manufacturer, and that amp had the same cooling issues as the LK500. Eimac would not even warranty tubes used in that amp. It was a very unpopular amp and faded from production quickly. Tubes traditionally, with his cooling systems, go over Eimac's seal ratings when just at idle. No RF drive, just quiescent current, puts them over rated temperature. He never measured temperatures. Fortunately most things missed are easy to correct.

    The problem is the radial or transverse airflow, and the very low fan speed he liked to use. I don't think he ever measured airflow or seal temperatures in his life.

    Traditionally transverse cooling will work, but it takes more overall airflow than chimneys and you have to plan what is around the tube to make sure all areas of the envelope, and especially pins, have adequate airflow. You'll have to open up the tube chassis at the outer edges away from the fan to let the air flow under the chassis without restriction, and just about double fan flow rate, to keep the envelope within seal and envelope limits at normal duty cycles. This means more noise, but longer tube life. The seals won't go over temperature at 250 watts dissipation per tube if you open up the far end of the tube chassis and double up the airflow rate of the fan.

    Just adding extra fans won't fix the real problems.

    At $200 that was a great deal.

    73 Tom
  7. KF7MJF

    KF7MJF Ham Member QRZ Page

    Tom, thanks for the input on the cooling. I opened up the chassis once so far just to peak inside. I've read a couple of modifications about increasing the cooling, and changing the fan. Is there a particular fan that is recommended for this, or simply look around for a fan with a faster speed?
  8. W8JI

    W8JI Ham Member QRZ Page

    You want more airflow at about .1 inches of static pressure.

    'What fan is in your unit, and is it run with full voltage???
  9. KF7MJF

    KF7MJF Ham Member QRZ Page

    AFAIK, the fan is stock, and I've yet to run it. It's from an estate, and was a working pull. I have no idea it's past use.
  10. WA7PRC

    WA7PRC Ham Member QRZ Page

    Omega has temperature indicating labels, crayons, cements and lacquers that you can use to see how hot various parts are getting. Too hot? More airflow! Or, you could just the method recommended for the "Umac 606 Phantasatron". ;)

    Attached Files:

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