rectfier tube to diodes

Discussion in 'Shock Brother's DIY Amps' started by Mongo Park, Nov 10, 2019.

  1. Mongo Park

    Mongo Park Tele-Holic

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    I have noticed some amp builds using Diodes instead of a rectifier tube like a 5Y3. What I am not finding is the specs on the diodes. I read people saying use a uf4007 diode, but are there different values. Do they come rated for volts and watts. So say I want to build a champ what uf4007 diode would I use, or does any garden variety do the job.
    Any help or direction would be appreciated.
    Cheers Ron.
     
  2. Snfoilhat

    Snfoilhat Tele-Afflicted

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  3. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Diodes have a current rating and voltage rating. They don't get a wattage rating since they aren't usually used in a position to do that type of work.

    I always use the 1n4007 but the UF is like fine. "ultra fast." In a rectifier position, and in anything guitar related, I don't think you'd notice a difference.
     
  4. Mongo Park

    Mongo Park Tele-Holic

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    Beauty, thanks for the quick and knowledgeable reply
    Cheers Ron
     
  5. Dacious

    Dacious Poster Extraordinaire

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    Also you"ll note some schematics showed stacked where there's several diodes in parallel, or there's 2,3,4 diodes end to end.

    This is because when you click a power switch and hit them with high AC voltage off the HT secondary it can flash them for an instant past their rating.

    Both stacked and ganged help individual diodes not instantaneously carry overcurrent, or where there's big current draw spread it.

    Diodes let you have one less circuit to worry about, but if you replace a tube rectifier with diodes be warned it will push up voltage some - typically 20-30 volts depending on what's either side. That will raise voltage throughout the preamp and power amp. Not usually a problem unless you're already pushing say EL84s or 6V6s pretty hard.
     
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  6. muscmp

    muscmp Tele-Afflicted

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    some people add the diodes to the rectifier tube so that if the tube goes bad the diodes still work.. that's one of robrob's mods.

    play music!
     
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  7. DavidP

    DavidP Friend of Leo's

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    AKA the "Dynaco mod"!
     
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  8. Wyatt

    Wyatt Tele-Afflicted

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    That’s not quite what they are for.

    The SS diodes are in series with the rectifier. In most cases a rectifier tube will fail and leave the circuit open and the SS diodes will not continue to operate.

    The SS diodes are there for the rare cases where the rectifier shorts “closed.” In those cases the diodes will protect the filter caps from seeing damaging high-tension AC voltage. The tube should be replaced ASAP because the higher voltages can damage other parts

    I specify “solid-state diodes” because a tube rectifier is a diode as well.
     
    Last edited: Nov 11, 2019
  9. Mongo Park

    Mongo Park Tele-Holic

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    Thanks for the added advice. I was starting from scratch so I will account for the higher Voltage.
     
  10. Peegoo

    Peegoo Friend of Leo's

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    Why not install a tube socket, and then use a Weber Copper Cap SS rectifier? You'll always have the option of popping in a glass tube if the notion hits ya.
     
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  11. Dacious

    Dacious Poster Extraordinaire

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    And it still has the advantage of retaining the heater, but not actually using it and reducing stress on the P/T. Should you ever wish to go back to a tube you can.
     
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  12. Viejo

    Viejo Tele-Afflicted Silver Supporter

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    Last edited: Nov 12, 2019
  13. mabinogeon

    mabinogeon Tele-Meister Silver Supporter

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    Late to the party, but those 1N4007 diodes are just so tiny.

    I switched to using RL207 diodes, which are a 2A version. I tried to use the 1N5408 3A, but it's too big.
     
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  14. Tele Slacker

    Tele Slacker Tele-Meister Silver Supporter

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    At the risk of resurrecting an old thread, I thought it may be a relevant enough to this thread to ask here. I am building a 5f1 using an Hammond 290AX. The PT allows either 325-0-325 or 275-0-275 secondaries. I’ve opted for the 275-0-275 secondary.

    I’ve wired things up, going through startup procedure, checking voltages. At pins 3 and 5 of the rectifier (“upstream” of each diode), I’m seeing 293-0-293... all good, considering no tube load yet. On pins 4 & 6 (downstream of diodes), I’m seeing 160-0-160. Not good. Cathode of diode (barred end) towards 4 & 6.

    Heater voltages good as well.

    What am I missing?
     
  15. Nickfl

    Nickfl Friend of Leo's

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    Did you switch your meter to read DC when you measured the voltage after the diodes?
     
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  16. Tele Slacker

    Tele Slacker Tele-Meister Silver Supporter

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    Excellent observation! I did not. Doing that, I’m at 135v (DC!!!) on each pin. This is my first time with diodes... is that voltage reasonable/expected?
     
  17. Nickfl

    Nickfl Friend of Leo's

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    Honestly, I have no idea. I would never have bothered checking voltage at that point without anything else hooked up. If I were you I'd go ahead and stick the rectifier tube in and fire it up through your light bulb current limiter and if there are no shorts move on to the next step.
     
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  18. robrob

    robrob Poster Extraordinaire Ad Free Member

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    1N4007 diodes are rated at 1000 peak volts, not RMS so putting two in series for a solid state rectifier is recommended.

    When using them as safety diodes with a tube rectifier the tube is the second rectifier and the tube and solid state rectifiers share the load. The diodes make life easier on the tube rectifier but you still get "real" sag.

    I definitely did not invent the rectifier safety diode mod.
     
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