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

    Hello Fellow QRO'ers,

    A Drake L4-B followed me home the other day. Missing a few items however I may have a line on the missing goodies. I do have one simple question to kick off this thread.....the drive chain is missing. Having never been around one of these, I am attempting to develop an opinion of what material the chain is made of, plastic or metal material of construction. The stock one looks to be white. I have found metal (#3 ball chain) online.

    The next item is the "AGC/ headlight push-pull switch" which also I have a line on. Hi! He simply needs to "find it" as I totally understand in that regard. Worst cast is that I could simply use a toggle switch and a pot.

    Chimneys. I heard that for the 3-500z tubes the Coleman lantern "You can also use Coleman’s lantern globes for their propane gas lanterns, part number R214D046C. If shopping at your local sports store, the box has a UPC number of 20071213 and on the globe itself is No. 277C043 3009." Found online, and from a few other hams, so I'll give that a try.

    The chassis is very clean for it's age. I'll include the serial number, PS boards have been re-capped, however have not preformed a close up inspection yet. The front panel looks fairly nice. Meters included. It's bottomless however, still need to find a lower cover or go ahead and bend one up at my local sheetmetal shop.

    So I'm taking any and all opinions. Drake Linear love / I'll miss your input sue!! Pictures up and coming.

    N4FZ likes this.
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The "chain" really is a metal chain connecting the input switch shaft to the main bandswitch shaft. Sounds like you found the right thing.

    If the amp hasn't been used in a long while, do you believe the tubes are still good? If one flashes, usually the 0.82 Ohm resistor in line with the B+ will blow open like a fuse and save damaging other components.

    What's an "AGC/headlight" switch? The L-4B has a front panel AGC pot (what most call "ALC") and a push-pull switch for STBY/OPER. It's weird that would be missing.

    Have fun, it's a pretty good amp!
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  3. W9GB

    W9GB Ham Member QRZ Page

    Drake L-4B HF Amplifier (using 3-500z glass RF tubes)

    Drake L-4B Rocker Switch repair / rebuilding

    Mark Olson, KE9PQ (Nationwide Radio Sales)
    Drake L-4B : Replacement Power & CW/SSB Switch Assembly
    Instructions by WB4HFN using the KE9PQ part

    Harbach Electronics stocks some L-4B Repair Parts.
    60EBDF1B-37A4-4450-ACED-537CCE3EBE2B.jpeg 6CE3E5E9-E688-4BF1-8587-200585C85474.jpeg
    The Red / Yellow Indicator Neon Lights are easy (Old Chicgao Miniature Light, CML) —
    still manufactured by VCC (datasheet). Price: $3.48 each
    Mouser Catalog Page — VCC Indicator

    Red: 1050C1 (1/2 watt, 125 VAC) : Mouser part number: 607-1050C1

    Amber: 1050C3 (1/watt, 125 VAC) : Mouser part number: 607-1050C3
    IF you need the VCC “Speed Nut”, that is part number: SN-0461C (datasheet)

    VCC SN-0461 : Mouser part number: 607-SN0461-C
    Last edited: Sep 27, 2017
    WB1E, N4FZ and N2EY like this.
  4. W9GB

    W9GB Ham Member QRZ Page

    Last edited: Sep 27, 2017
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  5. WB1E

    WB1E Ham Member QRZ Page

    WB2WIK, It came without tubes and chimneys. So I'll be shopping these out looking for fresh in service tubes as these do not last long unused on the shelf as I have heard. Perhaps RF parts and a 3 year warranty may be a good choice.

    W9GB, thank you for the free beer! The nationwide radio link is priceless for me right now, well priceless is a bad word. However Mouser is right up the highway, and normally I can have FedEx ground delivery next day.

    Thank you gents. I'm charging my PayPal batteries as I write.

    This chassis serial is #4556.

    The blower is simply not available, nor are any small blower wheels in that size. Blowerwheel.com did list something close, but nothing even close these days, so I now will go forward with plan B, the rebuilding of the original wheel. With close inspection, the wheel is showing degradation, half inch long cracking with the center 1/4" hub simply falling off. My plan is to install a lathe spun 3/32 or 1/8" round disk to flatten and reinforce the blower rear structure. By spinning this on a lathe, the fit and balance will be the best possible. Then screwed every 60 degrees (6 places) and the original hub pressed in. Well I could spin a one piece hub-washer out of 3/8ths plate. Need to check if I have some of that aluminum plate. The deal with the current squirrel cage blower wheel is that it's also egg shaped, but....goes back perfectly round when you press it flat on a table surface. So, one would think that all is good when & if it could be held in that position with such a washer-hub / sub-assembly.

    I'm not one for 100% correct in any of my restorations, but if it can be done with a little bit of extra work and not much $$, why not. Safety and performance Mods not withstanding.

    More soon.
    N4FZ likes this.
  6. W9GB

    W9GB Ham Member QRZ Page

    Drake L-4B Blower Wheel
    Question / Answer was addressed, here on QRZ Q&A, March 2017
    by Bill Peckhart, WB9ENB
    I did find a source for blower wheels that have the same Torrington part number.
    It is the same blower wheel but the hub is 5 mm instead of the 1/4" bore.
    The hub also has the same outside dimensions as the original.
    These can have the hub enlarged and then they are exact replacements.

    Metric Conversion (reminder) : 1/4 (0.25) inch = 6.35 mm

    Electric Trading Company
    1 Mercer Street (SoHo)
    New York, NY

    Single Inlet Blower Wheel 2-3/4" Depth; 1-1/4" Width; 5mm Bore
    SKU: 02240108-5mm-P-CCW-01
    IN STOCK : $20.99 USD

    How to Correctly Size Blower Wheels
    Last edited: Sep 28, 2017
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  7. W9GB

    W9GB Ham Member QRZ Page

    Push-Pull Switches, on a Potentiometer — also called a “Push Pull Pot” are still made —
    and in controls for electric guitars. Majority of these have a potentiometer value >100 Kohms.

    What is a Push Pull Pot ?
    Two electrically independent components are controlled by a single knob shaft.
    When the shaft is rotated, the potentiometer (and whatever it's wired to do) is operated.
    You can also pull up on the knob shaft, which will change the on/on switch from its "down" position to the "up" position. Remember, the pot and the switch are separate components, so there is no interaction between them unless you wire the push-pull pot to do so.

    CTS Potentiometers usually added a Push-Pull assembly to their standard Circular pots.
    These can often be repaired.

    Alpha Potentiometers (Taiwan) use a different assembly.
    Last edited: Sep 28, 2017
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  8. WB1E

    WB1E Ham Member QRZ Page

    It was in their "discontinued" section, didn't think to look there as I've been all over this site before. Thanks again!!


    Drake blower is back, ($48 bucks shipped) will just need to bore the hub to 6.35mm (1/4") accurately. OK trigger pulled on this one. The chain (if they'll let me order a sample) is on the way as well, but, I hope they don't ask me to order a football field's worth.

    Oh and WIK, sorry, the Headlight Switch, remark was referring to the AGC switch actually ALC. Push-Pull and rotate, you know like the old style headlight control.

    More soon....Doug
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  9. W9GB

    W9GB Ham Member QRZ Page

    Drake L-4B HF Amplifier : Standby / AGC Control
    Photo by Ron Baker, WB4HFN
    You can see the replacement control used by WB4HFN was a CTS 450 series “Push Pull Pot”,
    that he removed from a Heathkit HW-104.

    In the Drake HV Power Supply, the 5K ohm, 10 watt resistor is a common failure.
    When it goes bad, the resistor opens up, which takes away the ground potential for the high voltage filter capacitors. That in turn puts high voltage on the AGC control, which immediately burns the control open. It only takes a few seconds for the control to be destroyed.
    This is another component in the Drake L4B that can be hard to find.

    CTS Series 450 Rotary Potentiometer
    Industrial, 24mm Diameter, 1/2 Watt, Composition
    Mouser and Digi-Key are CTS distributors (CTS HQ : Elkhart, IN)
    Drake L4/L4B Blower Fan Repair/Upgrade
    by Gene McCalmont, W5DDW
    http://www.wb4hfn.com/DRAKE/DrakeArticles/L4B-Fan/Drake Fan Replacement.pdf
    Last edited: Sep 28, 2017
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  10. WB1E

    WB1E Ham Member QRZ Page

    So things are looking up. Got the blower wheel shipped. Funny thing, speaking with the sales guy, he mentioned that some other fella (5 blocks away) came down and purchased 2 blower wheels elated that they were the exact correct ones for his Drake L-4B.

    Also check out what I found for the replacement drive chain! Used for your ceiling fan pull chain, 5 bucks. At Lowes.

    The seller called today and alerted me that he has the bottom cover for me, plus the PS cage.

    I have a bunch of links to study, plus the schematic ongoing. Thinking of upgrading the power supply diodes with the 1N5408, however the original ones might be fine. Looking forward to testing the HV transformer on the variac for starters, and getting the Power Supply back up. Speaking of that, I'm looking for how the HV wire interfaces into the RF deck. The Nut is missing, I imagine that it had an O-ring or ferrule to hold the wire in place between the nut and the connector mounted on the Amp rear panel. I don't want to not have this assembly less that 100%. Is the HV wire striped back some distance, quarter inch? Need to get this part right. I may have to make a new nut and cast it from the existing thread with grease & epoxy, or simply change it over to a newer plastic 1/4" water or air fitting.

    73 for now, more soon.

    Drive Chain.jpg

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