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Broken VR-105

Discussion in '"Boat Anchor" & Classic Equipment' started by K9VKY, Jul 4, 2021.

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  1. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    VR tubes don't have a filament, but I wouldn't snort any residue from inside the broken bulb. Don't snort fragments of filament from a glass transmitting tube nor bits of the ceramic from an external anode tube. And it goes without saying, don't eat any shards of glass from the broken envelope.

    Otherwise, I'm about equally fearful of radioactivity from radio tubes as I am of RF radiation from my HF transmitter.
     
    N2EY, AD5HR and KA0HCP like this.
  2. KM1H

    KM1H Ham Member QRZ Page

    Not entirely in tube gear as NOS and good used replacements are readily available at reasnable cost.

    The octal based versions regulate at 5 to 40 ma while the miniature versions are 5-30 ma so a 10W zener is needed to replace an octal 105 and 150V and a 150V miniature tube running at full current specs....with a safe overhead. The zener is a one shot event to short it and in some apps they are capable of oscillation. The zener is not very good for a screen voltage supply in an amp when it comes to IMD.

    Also note that the internal gas may have deteriorated over time and not be very stable even at a constant current, its a good idea to test them in use.

    Im also a big fan of modern SS diodes in place of gas rectifiers such as the 866A which dont last forever and can be a bit temperamental with age and I wouldnt trust Fleabay used ones. A dollars worth of 1N5408's is rated at 5000V at 3 amps brand new from a major distributor.....6 from another for $1.02:D I replaced all my 866A's and 872A/8008's decades ago.

    Carl
     
  3. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    Plus, there's the 874, a 4-prong voltage regulator rated at 90V, 10 to 50 mA. I believe this was the first gaseous VR tube released on the commercial market, dating back to 1930 or maybe earlier.

    I have had good luck with the drop-in solid state replacements for the 866A and 8008 in my converted broadcast transmitter. Never had a lot of luck with a string of ordinary diodes in series; after a while, the whole string would would inevitably go off like a string of firecrackers. I did pick up a cigar box full of microwave oven rectifiers at a hamfest, and I have strung several of those together like you would ordinary diodes to make a HV rectifier, and they have held up for years. I believe microwave oven rectifiers are actually several carefully selected matched diodes in series, sealed in epoxy.

    I also use xenon gas direct replacement rectifiers for mv tubes, 3B28 for 866A and 4B32 for 872A. They seem less fussy than mercury, because xenon is already in gaseous form at room temperature thus no mandatory warm-up delay.
     
    N2EY likes this.
  4. KM1H

    KM1H Ham Member QRZ Page


    I didnt mention that one since few know about it. It is used in the PS of my 1934 RCA designed USN RAK/RAL regens.
     
  5. N2EY

    N2EY Ham Member QRZ Page

    The 3B28 is rated to operate from -75 degrees C to +90 degrees C (-103 degrees F to +194 degrees F)!

    There's also the 3B25. It's practically the same as the 3B38 except for maximum PIV being 5000 volts. In many applications, 3B25 is a drop-in replacement for 866A or 3B28.

    73 de Jim, N2EY
     

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