3-500z info

Discussion in 'Amateur Radio Amplifiers' started by KA2KDZ, Feb 20, 2012.

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  1. KA2KDZ

    KA2KDZ Ham Member QRZ Page

    Do some one can tell me how long i have to burn 3-500's before tx?.Plz email me ka2kdz@yahoo.com..Tnx in advance for ur help.john 73
     
  2. WA7ACE

    WA7ACE Ham Member QRZ Page

    You can let them "season" at idle for an hour or so before transmitting. I do just out of respect for the cash I paid for them.
     
  3. KG7MB

    KG7MB Ham Member QRZ Page

    I let them run 24 hours before I load them. Here is what RF parts has to say...
    Transmitting tubes generally require a "burn in" time to increase emission to its nominal value. In broadcast stations, 1-3 hours at rated filament voltage is allowed for burn in. This initial operation allows the getters, materials which absorb and hold residual gas, to finish the vacuum of the tube in its final operating environment. In an Amateur Radio amplifier, tubes will sometimes require 50-200 hours of accumulated "key down" transmit time to remove the residual gas and condition the filament for full emission. It is well advised to allow tubes to operate in standby mode (filaments on, no transmit) for 30 minutes before tune-up.

    The 811A, 572B, 3-500Z, 4-400, etc. utilize a thoriated tungsten filament, which is highly dependent upon sufficient filament temperature to provide adequate electron emission for normal operation. Emission increases as the thorium migrates towards the surface of the filament wire. This is why it is recommended to "burn in" these tubes before operation. Some amplifiers exhibit higher than rated filament & plate voltages due to excessive AC line voltage. This is often the case with older equipment rated for 115 or 230 VAC operated on our standard (higher) line voltages i.e. 120/240 VAC. Should you find the filament voltage is greater than the tube is spec'd for, adding a small amount of resistance in the primary of the filament transformer can reduce it to proper value. If the filament power comes from a multi-winding transformer (where additional windings are in addition to the filament winding), adding a small resistance between the filament winding and the tube socket will work.

    Note: excessive filament voltage above that specified for the tube will result in significantly shorter filament life.

    http://www.rfparts.com/tubeapp.html
     
  4. W1BR

    W1BR Premium Subscriber QRZ Page

    The gettering for the 3-500 tubes is in the plates. The tubes must be run showing some plate color
    inorder for the gettering to aborb residual gas. Running the filaments won't improve gassy tubes.

    Pete
     
  5. W8JI

    W8JI Ham Member QRZ Page

    10 seconds.

    If you run them 10 years, or run them 10 seconds, it will be the same.

    As K1ZJH correctly points out, they do NOT getter or condition from the filament, so it doesn't matter how long you cook them.

    If you want to getter them, you have to either intentionally arc them at very low current or run the anodes red hot.

    The same goes for emission life. If anyone tells you cooking the filaments before applying HV does something to improve emission, you better get a different tube. The ONLY reason to cook a filament for emission is because the tube manufacturer did not build and condition the tube properly, or the tube is near the fatal end of emission life. To condition the filament, it really has to be operated far above normal voltage.
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    You must have a lot of patience. I only wait about two seconds with 3-500Z type tubes. They seem to work fine after two seconds.

    I might try one second in the future.:p

    I've used a lot of 3-500Z amps from the SB-220 to today and never "cooked" them at all.
     
  7. KM1H

    KM1H Ham Member QRZ Page

    Agree, anything over 10 seconds is pure mythology. Its more important to be sure the filament voltage at the socket is well within the +/- 5% spec between no load and full load. The pair in my 1986 LK-500ZC are the original Eimacs and run at 4.85V under load using a stiff 240V line and output is still 1200W since Ive never pushed it higher and run 80-85W drive which is the IMD sweet spot for my TS-940.

    You DO need to get the anodes to color every few months at least to keep it gettered, the 3-500 of any make is one tube that does not age gracefully in a box or unused amp. Use it or lose it.

    Carl
     
  8. AG6K

    AG6K Guest

     3-500Zs and 3-500ZGs require no break-in period. Operating the filament does nothing to scavenge gas molecules inside the envelope.
     
  9. GM3SEK

    GM3SEK Ham Member QRZ Page


    The gettering for the 3-500Z is not exclusively on the anode. According to an Eimac source (retired and now SK), this tube also has getters at the base of the grid and the base of the filament. Those three getter areas are designed to work together, mopping up different gas species at their different operating temperatures.

    So the full reason why a 3-500Z needs to be operated at or near the rated anode dissipation is to bring all three getters up to temperature.

    That's probably true for all glass transmitting tubes, for the reasons stated above. But metal/ceramic tubes are different (which may have been the source of the original confusion).

    In a metal/ceramic tube, the getter is located on the indirectly heated cathode (or on the filament support structure of a directly heated tube) because those are the only parts of the tube that reach a sufficiently high operating temperature. Therefore the getter in a metal/ceramic tube can be activated by operating the heater/filament alone.

    Operating any tube at full anode dissipation will release more gas molecules which the getter must then collect; but it won't improve the gettering action in a metal/ceramic tube.



    73 from Ian GM3SEK
     
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