snubber circuit... on the OT primary leads / power tube plate pins ?!

Discussion in 'Shock Brother's DIY Amps' started by owlexifry, Sep 19, 2021.

  1. owlexifry

    owlexifry TDPRI Member

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    been tinkering with my 100w peavey/2203 clone thing again..
    had some great results after i put the 1000pf bright cap back in (ceramic this time), and a couple other cap changes.

    it is now very bright (holy crap). mostly in a good way.
    but i do want to tame some of the fizz/harshness without killing the good qualities of a pleasant high gain tone.

    i've already added these snubbers:
    - 22pf plate-to-cathode V1b (1st stage) ...considering increasing to 33pf / 47pf / 82pf / 100pf?
    - PI plate-to-plate snubber: 82pf 500v SM ...considering increasing to 150pf?
    - PI plate load resistor bypass caps: 120pf 500v SM, on both
    - NFB resistor (33K) bypassed with 100pf cap, "ice pick cap mod"-per robrob.

    been searching forums for a few days for topics that cover snubber caps / circuits.

    then i saw something i've never seen or seen discussed before:

    snubber circuit on the OT primaries / power tubes plate pins? wtf?
    snubbercircuit.PNG
    "published during the 1930s in the Radiotron Designer’s Handbook, and it’s called a “Snubber.” The idea behind it is to create a filter at the primary side of the output transformer that removes unwanted high frequencies while leaving the rest of the frequencies untouched. A relatively simple circuit, the Snubber connects between the two plate/anode connections on the primary side of the output transformer. Because only plate connections are required, soldering the Snubber directly to the power tube sockets at the same two locations where the output transformer wires connect to the sockets is an excellent solution. The great thing is that a Snubber requires only six parts: Two high-power resistors, two high-voltage capacitors, and two lower power resistors"

    from: https://www.tubesandmore.com/sites/default/files/associated_files/snubber_article_k-snub.pdf


    Is there a good reason why i haven't seen this before / why it doesn't seem to be that widespread?
    Does anyone actually endorse / recommend this snubber circuit? (the one above appears to be specific for an EL84 power section)

    not sure how well this would apply/translate to a 4x EL34 100W power section...

    another query: is it a bad idea to use ceramic caps as snubbers on V1b/input stage? (something something ceramic microphonic. could cause noise? ...but it's not a signal cap?) or does it not matter for snubbers?
     
    Last edited: Sep 19, 2021
  2. tubedude

    tubedude Tele-Meister

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    If your ceramic cap isn't microphonic I'd leave it. I prefer foil/film, or Styrene if the heat isn't excessive.
     
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  3. owlexifry

    owlexifry TDPRI Member

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    well, further reading suggests that apparently this type of snubber / "conjunctive filter" was designed for and is probably better suited to single ended/class A type power sections that don't use NFB..... makes sense
     
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  4. danlad

    danlad Tele-Meister

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  5. danlad

    danlad Tele-Meister

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    It's interesting on the discussion above that some of the old timers seem to say this idea crops up every so often! Does seem to suggest it's worth trying. Wonder if it was something that serves a purpose but ultimately using negative feedback instead became the de facto norm?
     
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  6. dan40

    dan40 Friend of Leo's

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    I have used that exact circuit in my Marshall 18 watt style build. It does work but I'm not sure how well it would work with the nfb as you mentioned.

    Marshall has used ceramic snubber caps on v1 in some of their MV amps. I agree, if it's not showing signs of microphony I would leave it.
     
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  7. owlexifry

    owlexifry TDPRI Member

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    many thanks for the responses.

    i'm starting feel a bit silly for posting this thread at all...

    overall doesn't seem like a sensible idea for a push-pull power section with NFB (which I have).


    for V1 snubber cap, i recently changed it from an old, heavily used 47pf (silver mica) to a new 22pf (ceramic), and banded/covered the cap in heatshrink in an effort to minimize vibration to the cap.
    i'm wondering how significant this cap change may have been..
    not actually sure what the "stock" snubber value is, since i've never managed to find one on any 2203 schematic...

    probably just gonna try different values (33pf, 47pf, 100pf) until it sounds right.

    also, i read that for a plate snubber, apparently it makes no difference whether you shunt plate to either B+ or cathode - how true is this? which is "better"?
    (practically, going plate to cathode is simplest, can just solder leads direct to tube socket pins)
     
  8. dan40

    dan40 Friend of Leo's

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    I have read some of Merlins info on this and he states that the cathode potential is very close to ground so either method will work just fine. You can also snub directly across the plate resistor and see if you like it.
     
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  9. owlexifry

    owlexifry TDPRI Member

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    sounds good, thanks.
     
  10. printer2

    printer2 Poster Extraordinaire

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    With NFB you can try rolling off the highs along with the snubber. So rather than the NFB fighting the snubber you can get them to work together.
     
    Last edited: Sep 22, 2021
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