Drake L4-B Resto

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

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  1. WB1E

    WB1E Ham Member QRZ Page

    Offers for free stuff? And Belton hamfest is right around the corner. That is tempting Lou.

    I wrote: with the pot to CW gives about 20% more output, Not anymore if ever, I was under the impression that it was somehow working with no ALC cable connected. Perhaps simply the tubes coming up to and gettering. There was dynamic changing by the minute of these tubes. Even after hours of filament ON time.

    The TX RX relay is not acting nice, dirty contacts on Receive. Cleaning tonight. Perhaps a replacement even.

    On SSB: 950 Watts PEP last night, tuned up with 80 watts CW excitation! 100 watts CW tune up makes stuff happen :) I swear that I saw 18 Ohm (3x in parallel) resistors inside those Drake parasitic chokes. Well I'll be in there later today and attempt to verify. If so that would make these combined... a 5 Ohm/ 15 Watt resistor.
     
  2. WA2LXB

    WA2LXB XML Subscriber QRZ Page

    CW-Tune into dummy at 40M, 1.13SWR: 1850 plate volts, plate dipped, load peaked to 0.565 plate amps, 105W exciter, 906W out with 3-500ZGs
    SSB-Same as above, 2650 plate volts, AGC adjusted to 0.580 plate amps, in SSB position, shrill whistle, 105W exciter, 1350W out.

    No ALC cable between IC-7300 and L-4B. Ameritron ARB-704 soft keyer being used.

    I'm not convinced I have the tank tuned perfectly. Going to use CW pulser method next round. http://wb4hfn.com/DRAKE/DrakeHamvention/2015/Drake_Forum_Slides_2015.pdf
     
  3. AI3V

    AI3V Ham Member QRZ Page

    No way are those DC input and RF output numbers even remotely accurate.

    Rege
     
  4. W1QJ

    W1QJ Ham Member QRZ Page

    You guys have to realize that the tuning instructions for most vintage amps, especially the ones with dual voltage settings are no longer valid. Those instructions were geared to the old power regulations. They had to use instructions that did not cause you do go beyond the one kilowatt DC input regulation. Since the power regulation has changed over the years it makes those instructions obsolete. Basically the way to do it these days is to tune for maximum output with full drive power and don’t exceed 1500 watts output or 900ma of plate current whichever comes first. Lastly slightly over couple the load.
     
    WB1E likes this.
  5. WA2LXB

    WA2LXB XML Subscriber QRZ Page

    Yep, thanks Lou...got it...and thanks for the "1500 watts output or 900ma of plate current whichever comes first. Lastly slightly over couple the load."

    I ignored the 1KW power limit curve in the manual. I wanted to follow the manual to the letter to make sure I didn't exceed any tube or amplifier design limits. Now that I'm comfortable with that process, it's time to layer on tuning for maximum FWD power without exceeding 220 grid MA.

    BTW, I'm using an LP-500 to monitor amplifier SWR and power to the dummy.

    I would appreciate your thoughts on the methods below...which are very similar other than exciter power levels at the beginning.

    At about 9:30 in this video shows tuning for max FWD power in CW mode:

    AD4U writeup in eham wasn't specific to CW or SSB:

    Tuning the L4B...can be accomplished in just 3-4 seconds.

    1. Set the L4B bandswitch to the proper band

    2. Preset the L4B tuning control in the center of the band segment arc indicated on the panel behind the knob

    3. Preset the L4B loading knob to around the 10-11 o'clock position

    4. Apply 100 watts drive from the exciter

    5. Adjust the L4B tuning knob for maximum power as indicated on the L4B wattmeter. If it was preset as stated in #2 above, this will be a very slight adjustment.

    6. Adjust the L4B loading knob for maximum power as indicated on the L4B wattmeter

    7. Re-adjust the L4B tuning knob for maximum power as indicated on the L4B wattmeter

    8. OPTIONAL - Adjust the L4B loading knob very slightly clockwise until the power output JUST starts to drop. I used a Drake L4B for over 20 years. I never did #8 but many today seem to think it improves the quality of the signal.

    Remember the Drake L4B was never intended to be a 1500 watt OUTPUT amp (1200 is max) nor was it meant to be operated on the WARC bands. It was built in the days when the legal limit was 1000 watts INPUT on CW and 2000 watts INPUT on SSB and before we had the WARC bands.
     
    Last edited: Mar 25, 2018
  6. W1QJ

    W1QJ Ham Member QRZ Page

    1. Set the L4B bandswitch to the proper band

    2. Preset the L4B tuning control in the center of the band segment arc indicated on the panel behind the knob

    3. Preset the L4B loading knob to around the 10-11 o'clock position

    4. Apply 100 watts drive from the exciter

    5. Adjust the L4B tuning knob for maximum power as indicated on the L4B wattmeter. If it was preset as stated in #2 above, this will be a very slight adjustment.

    6. Adjust the L4B loading knob for maximum power as indicated on the L4B wattmeter

    7. Re-adjust the L4B tuning knob for maximum power as indicated on the L4B wattmeter

    8. OPTIONAL - Adjust the L4B loading knob very slightly clockwise until the power output JUST starts to drop. I used a Drake L4B for over 20 years. I never did #8 but many today seem to think it improves the quality of the signal.


    The above procedure is what I would recommend which is essentially what I stated. His #8 is what I also mentioned and isn't a bad idea with some radios that have some over shoot problems. He is right by saying that the L4b and other amps like it were never to be intended as 1500 watt amplifiers, however for casual SSB without heavy processing a full 100 watts of drive should be no problem for these amps. The weak link in most of these vintage amps is the transformer. They can supply plenty of power but only on a very slight ICAS type of service like casual SSB. Don't expect contest type operation with voice keyers and processing because the transformers will eventually give out. For DXing like calling in pile ups full bore should easily be possible. Also keep in mind that the 225ma of grid current is a 24/7 key down rating so a mode like SSB the grid current could be considerably higher. In one case Eimac Ok'ed 400ma of grid current for SSB peaks for a pair of tubes. For plate current .9-1 amp is also no problem for a pair on SSB either. A pair of 3-500's should be good for 2000w output of pep ssb power under the right design of the amplifier. Henry made use of this parameter very well in some of their amplifiers. Over dissipation is what kills tubes not power output.
     
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  7. WA7PRC

    WA7PRC Ham Member QRZ Page

    ...and adjust drive to make the LINEAR amplifier operate LINEARly.
    N8LP's LP-500/LP-700 also has a VERY nice envelope & trapezoid display: http://www.telepostinc.com/LP-500.html
     
  8. WA2LXB

    WA2LXB XML Subscriber QRZ Page

    Yep...gonna get to that trap display soon-thx!
     
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  9. WB1E

    WB1E Ham Member QRZ Page

    My Murch tuner has been complaining lately, and rightly so Hi! So after attempting to use my newly acquired SA2060A which promptly started singing at anything over 300 watts, It was time to go over the Murch UT200A. Discovered a long outstanding issue with a bad solder joint on the output PL239, finally, now the tuner is back in service.

    I've been holding out at Ig= 220mA/ & Ia= 600mA for the below values. In H.V. 2.6kV

    In AM mode, the plates have been getting red about halfway up after 30 seconds. Running 350 watts (AVG) / 900-1000w (PEP)
    In SSB mode, around 900 watts (PEP)

    Thx again Lou! These L4B's are working great.

    Doug
    N5DMC
     
  10. W1QJ

    W1QJ Ham Member QRZ Page

    Doug, what do you mean about the SA-2060a "singing over 300w"? I have a 2060A and I have run it into an 80 meter Zepp fed with ladder line at 1500 watts on many different bands with no pain no strain. I think it is a very fine tuner.
     

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