Drake L4-B Resto

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

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  1. WA2LXB

    WA2LXB XML Subscriber QRZ Page

    Hi Lou!

    Agree. Factory spec should be close to achievable if all is well in the amplifier. If not, then I'm either loading it wrong, or I'm not matching the exciter to the L-4B properly or there is some other technical issue. As I'm a relative noob to linear amps-having spent more time freshening it up than operating it, I'll keep trying to load into my 2KW fan cooled dummy, following the L-4B manual, and if I can't get 1.0KW CW and 1.2KW PEP or more on SSB, then I'll have to reach out for help.

    I'm only seeing about 800W out in CW mode with 100W exciter input into a 50 ohm dummy. That said, I didn't hit the tuner button on the 7300 when I was exciting the L-4B-Doug remembered to do that. More test runs to make, hopefully this weekend.

    My wife walked in to bring me a cup of tea the other night right after I had concluded 800W key down carrier into the dummy for 60 seconds. She said: "It smells like something is burning"...I told her that's the sweet smell of 50 years of ham memories being re-awoken...and yes, it's supposed to smell like that:cool:

    Lou, what technique do you use to calibrate the vernier pointer on the Plate capacitor on the L-4B? Do you use the method mentioned in the manual, or could an antenna analyzer (i.e. AA-600) on the RF input with a dummy on the output be made to perform the task?
    Last edited: Mar 22, 2018
  2. W1QJ

    W1QJ Ham Member QRZ Page

    If you are getting 800 watts of key down carrier in the CW mode then you should easily get 1000watts + in SSB mode key down. But don't forget you will have to re-load the amp when you switch modes. The loading will change for sure and when you "tweak" it the power will rise even more than after you switched the switch. With the pointers, they are set so that when both the load and tune caps are at full mesh (full ccw) the pointers will be a the full CCW position on the scale. Depending on your antenna load will determine where the tune cap will point on any given band, you may want to adjust that so on all bands it points in the region on the scale. The load is arbitrary.
    WB1E and N4FZ like this.
  3. WB1E

    WB1E Ham Member QRZ Page

    itsalive-min.jpg Hello also Lou!

    With these Chinese tubes....?

    So far only exceeding recommended Ia to 650mA, Ig=220mA, Exciter in CW at 75 watts input, after 20-30 secs, dull red glow. Not in AM with 30 watts in (always tuned in/out to 1:1)

    One thing Hugh that I did notice, is that after I do preform the L4B tuneup in CW and go for the BIG power in HV (ssb-red switch up) mode, my SSB power is finally up around 800w PEP with the LOAD at about 12 o'clock. If I tune up in the AM (30 watts Avg in) from the exciter, I can only get .350mA Ia or 450 watts PEP in HV mode. and the LOAD knob is always fully CCW. So I'm tuning up in CW, more tonight.

    Last edited: Mar 22, 2018
    KD2ACO likes this.
  4. W1QJ

    W1QJ Ham Member QRZ Page

    Doug, when you load up for AM you must first load up at full carrier power of 100 watts, you never load at the carrier power.
  5. WB1E

    WB1E Ham Member QRZ Page

    Hello Lou,

    That's all she's got captain. :) Ft-2000D AM output power is 30W (avg) So am I doing the right thing loading up at 100W (avg) in CW mode? The L4B always tunes up better doing it this way at the higher (CW) input to the Amp from the exciter.

    from Yaesu's website...."The FT-2000 and FT-2000D provide a full 100 & 200 Watts of power output (AM: 25 W) on the 160-6 Meter Amateur bands, and the U.S. version includes a special memory bank containing the five 60-meter channels, as well. "

    link https://www.yaesu.com/indexVS.cfm?c...02&encProdID=66EA91711DFB68C03DED4AD35153E12C

    I know this L4B will love life connected up to my Valiant II. And to my Swan 500. But will be sure to not overdrive it.

    Last edited: Mar 22, 2018
  6. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Hi Doug,
    It's been fun watching you bring the amp back to life! It's beautiful.
    I believe what Lou meant was to tune the amp in CW to full power then switch to AM...

    Thanks for sharing your rebuild.
    WB1E likes this.
  7. WB1E

    WB1E Ham Member QRZ Page

    It's the the instead of that I think is what caused the confusion on my end. I had 500 watts of AM I think, or maybe it was a dream. Either way, today on 3890, I'll give her a try. She'll do 300w at least.

    KD2ACO Chris: I can't express how much fun this has been, taking my time, and coming out on top with a real sweet looking and working Drake L4B. Thank You Sir!

    I will keep this thread going until I get the bugs out, or I should say my perceived bugs. Plus a list of mods that I may or may not do. I have a Hamfest (Belton, TX) coming up in which I will be consulting with more experts regarding the potential fate of this one.

  8. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I finally got some AM going but I had to buy it instead of build it due to a crushing work schedule, (radio du plastique). I'm keeping an ear out for ya!
    WB1E likes this.
  9. W1QJ

    W1QJ Ham Member QRZ Page

    Yes, that is exactly what I meant.
    WB1E likes this.
  10. W1QJ

    W1QJ Ham Member QRZ Page

    I have a Drake L4/L7 power transformer. It is said not to be good. I don't know. Probably can be rewound. If someone wants it I will let it go for Shipping and handling.

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