Drake L4-B Resto

Discussion in 'Amateur Radio Amplifiers' started by WB1E, Sep 27, 2017.

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  1. AA2AS

    AA2AS Premium Subscriber QRZ Page

    ozone? oh no! I see a clipperton there?
    WB1E likes this.
  2. WB1E

    WB1E Ham Member QRZ Page

    Yea, the Clipperton plays very nice with the Murch, but not the Drake L4B, just too much voltage. Same for the SA2060A tuner. Even after a complete going through. The original silver plating is beautiful after the aluminum & baking soda, in boiling water treatment which worked excellent as does the tuner, I'm sure. But with my OCF 160m Vee Beam, I'm pushing the capacitor spacing as arcing is way out of control over 400 watts carrier. Especially on voice peaks.

    So I'll be looking to build up something more substantial for the AM mode especially.

    Happy Easter

  3. KM1H

    KM1H Ham Member QRZ Page

    Naturally since both had the same owner but since Dentron never had a 3-500 amp I fail to see the significance.

    Both brands built stable amps even with the added gain of direct grounded grids. Heathkit did not and toss in that they were kits built any which way the negative FB was desirable. Thousands of the SB-200 and 220 family are still in daily use without Hammy Hambone mods of questionable benefit. Toss in the TL-922/922A. They all had an effective grid fuse since those chokes saved many tubes from destruction.

    The L4/4B used such low DC resistance grid chokes that were useless for any purpose. Interesting to note is that the PS were different.

  4. W1QJ

    W1QJ Ham Member QRZ Page

    Yes, I know there were no 3-500 Dentron amps but they did have a pair of 572b's like the Heathkit SB-200. In the SB-200 the grids were floated on caps but Dentron directly grounded them and used conventional biasing. That was my point.
  5. W9JSW

    W9JSW Ham Member QRZ Page

    Bryan, trying to find this drawing... @WA7PRC
  6. WB1E

    WB1E Ham Member QRZ Page

    Just an update, the Drake L4B is working perfectly. No more OCF antenna, now cut to 3870Mhz. Those big heaters are gone finally. Now I using a NTE-5248A (7.5v-50watt) Ziener for the bias. Best thing I have ever done to this amp. She is finally under control and has no bad habits. Actually for sale !
  7. W9JSW

    W9JSW Ham Member QRZ Page

    Can you show a pic of how you installed the zener?
  8. W1QJ

    W1QJ Ham Member QRZ Page

    The zener simply goes in series with the B- to the CT of the filament transformer. Observe polarity that's all.

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