Two amps (two 3-500z), different drive input power required

Discussion in 'Amateur Radio Amplifiers' started by K5VV, May 28, 2016.

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  1. W8JX

    W8JX Ham Member QRZ Page

    The temperature of that air at any given dissipation level depends entirely on airflow rate. Plus, the cooling on anode connection is equally applied from all side as well unlike a fan merely blowing air across it from side. Once again it is foolish to suggest that designer of tube does not know best method to cool it.
  2. AF6LJ

    AF6LJ Ham Member QRZ Page

    The point you are missing is this.
    The air system sockets and chimneys are only a recommendation they are not required.
    You haven't successfully provided an argument against the method used to cool those tubes. The uneven cooling argument doesn't wash, Aluminum is a decent thermal conductor and will provide enough cooling with little difference between the fan facing side and the side that faces away from the fan.

    I was hoping you could provide some evidence (real, measurable evidence) At this point I see no productivity in continuing this discussion.

    Please red the datasheet and understand the difference between a requirement and a recommendation. No 3-500Zs have failed due to overheating in a properly tuned, maintained, and driven SB-220.

  3. W8JX

    W8JX Ham Member QRZ Page

    The point you miss is that the designed operating limits are for with a envelop not in free air. (some amps like L4/B and AL82 etc use proper cooling) There are many 3-500z tubes used in SB220 and similar amps that have needed to have there pins re-soldered because they overheat without proper cooling. To some the solution is to use silver solder on pins rather than address the cause of problem ie lack of PROPER cooling.
  4. AF6LJ

    AF6LJ Ham Member QRZ Page

    I explained the exact cause of the overheating pin problem.
    Operate the amplifier with the front tilted up an inch like they were intended and the solder won't melt. There is enough cooling on those pins when the amplifier is allowed to breathe.
  5. KM1H

    KM1H Ham Member QRZ Page

    You never were very big on technical knowledge over the years you have been on here and elsewhere and apparently havent improved much.

    Even the Eimac data shows the tube is less efficient at low voltages as is common with their line from the 4-65A to the 3-1000Z. Study the tube curves for an understanding.

    Run the amp at 1000W INPUT on the CW position and at 2000W INPUT in the SSB position by following the manual procedure. When doing this the tank impedances are equal but it does not meant the efficiencies are.
    Do not change the drive power either.

    That is a good procedure to sound like a CBer if you are running the same drive power at half the INPUT power.
    No more than 100W PEP should be used to drive that amp which is a nominal 25W carrier and that should result in 1200W PEP in the SSB position which is way more than the transformer can handle except for a short time. About 15-20W carrier should be the limit and you can use an inline attenuator if the drive cant be reduced. AND you will be a lot cleaner.

    I use primarily audio modified controlled carrier rigs for my 2X 3-500Z, 4 X 572B, 2 X 8875, and other power supply limited amps which further reduces the heat a lot. Increased bias and improved cooling is also used to further reduce heat and improve efficiency to the point that a Clipperton L can run all evening at 1000-1200W PEP in roundtables with only a trace of anode color on voice peaks with Chinese tubes and a happy transformer.

    Id suggest either learning the subject or going back to that unmoderated forum you came from.
    AF6LJ likes this.
  6. KM1H

    KM1H Ham Member QRZ Page

    Eimac approved the axial fan cooling for the 4-400A as far back as the Johnson T Bolt plus various 3-400Z and 500Z amps.
    Its funny that only a kit built amp by those who cant read instructions have pin problems.
    AF6LJ likes this.
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    As I remember, and I did build an SB-220 from a kit, it was a pretty easy kit and the only thing complicated that I recall was the input tuned circuit subassembly which is up at the front panel and once installed has stuff in the way. It was easy to build it "right," but of course soldering techniques and abilities vary a lot.:p

    I never had any kind of pin overheating problem with mine, but then sold it before the original fan had any problems. If I had one today I'd probably change the fan to a new, modern, higher-speed (even if noisier) ball-bearing fan and try to remember to clean the blades annually -- which I think a lot of people don't do.

    I didn't like the SB-220 enclosure, which required removing the feet as well as screws in the back and then jockeying the thing about to slip the chassis out or the cover off. But that had nothing to do with the fan.
    AF6LJ likes this.
  8. WA7PRC

    WA7PRC Ham Member QRZ Page

    VA7JW produced a method of slowing the SB-220 fan during idle periods. I contacted him and queried him about the actual wire-glass seal temperature during idle. Using thermocouples, he measured the temperature of the two filament wires adjacent to the seals and found the worst-case to be 50°C below the 200°C limit.

    David K5DBX added a shroud to the fan and found an increase in airflow and a decrease in noise.
    AF6LJ likes this.
  9. KM1H

    KM1H Ham Member QRZ Page

    The fan was fine as long as the darn thing got cleaned and lubed once in awhile. Based upon the over 300 SB-220/221/HL-2200 Ive converted to 6M or repaired for HF many were in a heavy smoking and/or dirty environment. Brown tubes and fan blades from nicotine covered with dirt didnt help the cooling nor did the idiots who left off that little aluminum strip off the back of the cover which is there to direct airflow to the pins.
    Other idiots didnt bother to read the fan blade placement on the shaft instructions either.

    Going to a too high speed fan can actually reduce the cooling. That amp was actually engineered well but decades of incompetents posting idiotic mods and other changes will live on the Web forever and infect others.

    The quality of the soldering of the filament circuit wiring is another sore point with me.

    Id warrant a "guess" that most SB-220 family complaints can be traced right to the builders and later owners who havent learned how to read the manual nor have a clue how to use the amp.

    AF6LJ likes this.
  10. W8JX

    W8JX Ham Member QRZ Page

    Funny how we are talking about 3-500z tubes that was designed to work with chimneys for design ratings and you tilt/switch to 3-400z which dissipate 20% LESS heat.

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