0.82 ohm HV fuse

Discussion in 'Amateur Radio Amplifiers' started by WB1E, Jul 28, 2018.

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  1. WB1E

    WB1E Ham Member QRZ Page

    Well it could of been cat hair, but my Drake L4B blew the 0.82 ohm HV fuse. (It was as loud as a 22 round) And I can't remember where to find any. EBAY & Mouser carry them, however I'll be darned if I can track down any whatsoever.

    This, just before I was filling out Mom's life insurance papers, claim form. Could be an how you say....Oman?

    The rectifiers, & secondary winding all look good. Next will be checking the RF deck rather than simply soldering in another fuse.

    So, this is it for the HOA antenna test site. The flat top 75m long Vee Beam has been hidden all the while.
    Updates on the L4B's status will be delayed for a couple of months until the dream shop & tower goes up!

    In the mean time if yall could remind me where the best place to get some replacement 0.82 Ohm HV fuses, I'd thank you :)

    Doug
    HV Fuse-min.jpg
     
    Last edited: Jul 28, 2018
  2. W1QJ

    W1QJ Ham Member QRZ Page

    I’ve got them. Send me an email at gudguyham@ail.com. You are correct, they are s special type of fuse resistor. Lou
     
  3. WB1E

    WB1E Ham Member QRZ Page

    Again Lou, you are the greatest! 73

    Doug
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I have some also, if Lou ever runs out!

    BTW the cause of the failure wouldn't be anything in the power supply; it's there as a "glitch" resistor to protect the power supply and other components from a short circuit (or arc) in the RF circuitry. An internal arc in one of the tubes, even a very momentary (milliseconds) ion arc, will cause it to blow open.

    Usually it's an indication of a failed 3-500Z.
     
  5. W1QJ

    W1QJ Ham Member QRZ Page

    Doug, just noticed the photo, that’s NOT the original resistor from the factory. The ones I have are the original ones that Drake and Heathkit used. They have a special two letter designation that I don’t recall.
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It's type BWH 0.82 Ohms, 2W and it's not carbon, it's wirewound internally.
     
  7. WB1E

    WB1E Ham Member QRZ Page

    Ah HA, I was interested in what the wattage value was.

    It happened after a 5 minute warm up, then keyed up to do a fine tune at around 60 watts drive. The amp was already tuned up on 75m the night before. Was just checking on a 30Khz change and attempting a quick peak.
    I checked the HV input to ground and saw around 12 MOhms, so everything is being packed up at this point, hate to pack away something that needs repair. I guess I can heat up the filaments awhile looking at the back panel HV input to ground for DC Ohms. At least get the tubes hot and have no HV present.

    Not surprised given that the original RFC / capacitor combo had shorted out that the HV 0,82 resistor-fuse was not stock. I'll have to do a post mortum on that little bugger and shoot some pics and see what she's made of.

    Thank you everyone whom replied so far with support & acknowledgment. My cat (like Lou's she is white) loves to hang out on the floor with the power supply, maybe because it's warm.

    HERE is one thing this did just the other day that sounded very weird. Apx 2 operating hours ago, when I switched he HV to low from the high position, there was a sound from the RF deck that sounded like a stepping on a frog, 200Hz constant tone lasting for 2 seconds. Capacitor maybe?

    I just witnessed about 3 months ago Mouser actually had these in one of their advertisement emails. Ohmite perhaps, I'll have to browse my old emails from them and get back here and post.

    'yall are the greatest, but for now it's pack it up and go. More soon-

    Doug
    N5DMC
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The wattage rating isn't as important as the construction. As Lou pointed out, the one in the picture is definitely NOT original and looks like carbon or metal film -- that won't do the job well. You really want to use type BWH which is a molded wirewound.
    I think more likely an arc. An arc can sound like a low-pitched but sharp-edged hum (more like a "buzz"). A low-energy arc inside one of the tubes can sound like that, but eventually something will blow (in this case, the .82 Ohm resistor).
     
    WB1E likes this.
  9. WB1E

    WB1E Ham Member QRZ Page

    Update....

    I have not done anything yet. With moving and cervical vertebrae fusing, this ham is without any shop and nothing but packed boxes currently.

    A low pitched flutter sound is another way I would describe the sound that occurred about 2 operating hours before the resistor blew. I have had no chance to check anything out internally as of yet. Soon, hopefully I'll have a shop back up and running and will have my way with this sweet Drake L4B. I agree, could be a tube. I may also send the pair of 3-500's back to Merit at RF parts and see what he thinks while I have the time. The sockets were in wonderful shape and will these a good look over as well.

    Radiculopathy is a bad deal, ongoing.

    - Doug
     
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    I would clean up that solder joint and get rid of the sharp edges and make a better ball joint.

    [​IMG]

    Have Fun.
     
    WB1E likes this.

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