Purpose of resistor, Marshal 18W lite build

Discussion in 'Shock Brother's DIY Amps' started by Diverted, Jul 17, 2019.

  1. Diverted

    Diverted Tele-Meister

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    Hi all,

    First off, sorry. I don't have a schematic for this amp, just a layout. Looked around but could not find one; would have rather used a schematic to be honest.

    Anyway when I started putting it together I noticed a 220K resistor between the diode rectifier and first filter cap, attached to the standby switch (I built it without the switch). I'd never seen such a large resistor in that spot and thought initially it would kill the B+ voltage.
    Well that's what happened. Fired up for the first time today and I was only getting max 75VDC at the first filter cap before it started settling down lower. So I pulled the resistor and hooked the rectifier DC out directly to the first filter cap. Now the amp's getting the DC it should, low 300volts, and sounds killer.

    Anyway I'm wondering if anyone tell me why that resistor would be 18WPlexi-Layout.jpg there?

    Thanks!
     
  2. drf64

    drf64 Poster Extraordinaire Silver Supporter

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    No idea. Is this a Ceriatone? I wish Nik would publish schematics. I don't know if he sends one if you buy a kit.
     
  3. Diverted

    Diverted Tele-Meister

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    It looks like a Ceriatone but it’s not listed on their site so maybe a discontinued item?
    I really like it, put in a tone stack bypass switch and it really gets raw.
    Only thing I don’t like is the master... I may change it to a larmar PPIMV.
     
  4. Tom Kamphuys

    Tom Kamphuys Tele-Meister

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    Is it supposed to drain the caps? Value and power look appropriate for that...

    At the Build Your Own Clone, Trinity Amps and Tube Depot site you can find lots of info btw.
     
    Last edited: Jul 17, 2019
  5. VintageSG

    VintageSG Friend of Leo's

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    I think it's a holdover from valve rectifiers, designed to keep the cap charged so there isn't a surge current causing flash over when the standby is used, or a drain so you don't get tickle-finger when prodding about.
     
  6. Diverted

    Diverted Tele-Meister

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    If it was supposed to drain the caps I would have thought it’d be from the first filter positive to ground.
    As laid out in the pic all it does kill off most of the B+. Really strange.
     
  7. tubedood

    tubedood Tele-Meister

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    A few of the other layouts and schematics seem to show a 220k in that position to ground... maybe a typo on this layout?
     
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  8. Diverted

    Diverted Tele-Meister

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    Gotta be. Only thing that makes sense?
     
  9. D'tar

    D'tar Friend of Leo's

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    I don't know the intentions of that resistor but one might think to use it as pop reduction across the standby switch. This is obviously not how it is utilized on the layout. Another option would be a sag resistor but the wattage would be greater and different value. I would omit and carry on. YMMV
     
    Last edited: Jul 17, 2019
  10. robrob

    robrob Poster Extraordinaire Ad Free Member

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    It's got to be an error. Just delete it.
     
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  11. Tom Kamphuys

    Tom Kamphuys Tele-Meister

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    I agree. Looks like an error.
     
  12. Tom Kamphuys

    Tom Kamphuys Tele-Meister

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    tubedood likes this.
  13. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    Isn't the 18w lite from the 18watt.com build site?
    They should have lots of info/ schematics/ layouts there.
    I tried to join numerous times but my login never worked so I gave up.
     
  14. tubedood

    tubedood Tele-Meister

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    Speaking of the 18 watt project... I am thinking of one of these builds in the near future. They seem to be great amps!
    Do keep us updated on your build Diverted!
     
  15. Diverted

    Diverted Tele-Meister

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    Yup. Took it out 10 minutes after firing up amp for the first time. Plays great now
     
  16. Diverted

    Diverted Tele-Meister

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    I’ll post some pix and vids soon as it’s all together. Love it so far.
     
  17. Bitsleftover

    Bitsleftover Tele-Meister

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    Pop reduction as D’ter said. It’s in parallel with the open switch, (ie shorted out) not in series with it.
    No requirement with the switch removed.
    I. cant see how it would drain a cap? It’s not connected to a ground anywhere.


    Sent from my iPhone using Tapatalk
     
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  18. Diverted

    Diverted Tele-Meister

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    Thanks. To clarify, in the layout I posted at the beginning of the thread it looked to me like it was connected in series after the switch, running from rectifier to first filter. With switch on (or in my case, no switch but instead hardwired to rectifier) it was DEFINITELY reducing the DC coming out of the rectifier before it hit the first filter.

    In the schematic later in the thread it was running from the first filter to ground and would quickly discharge the caps once power was turned off.
     
    Last edited: Jul 18, 2019
  19. Diverted

    Diverted Tele-Meister

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    Nope, I got it here. Lots of stuff on this page:

    http://rh-tech.org/public/18-Watt/
     
  20. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    I'd bet many or most of that content was pirated from this (below linked) site, which is where the 18w build community shares, discusses and develops designs for 18w variants.
    I'm not sure who originally created the 18w TMB, though often Ceriatone is credited with the published TMB circuit.
    You can sort of tell that these amps were designed by a hobbyist community when you note that they put the PI tube in between the two preamp tubes, instead of closest to the power tubes.

    I think the 18w Marshall lite and TMB variants are foremost examples of a community based product that didn't originate in a single designers shop.

    18watt.com also has sister sites including SEwatt.com, which did a lot of tweaking of the popular Epi VJr when it first hit the market.

    AFAIK the 18w lite originally came from those Valve Jr chassis and PT modded for a second power tube into an 18w Marshall variant.
    18watt.com and (SEwatt.com) really is the place to go for this stuff, though your question did get answered here.
    I'm not sure what they are up to these days though, as I haven't visited there in a while.

    https://www.18watt.com/

    http://sewatt.com/
     
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