SANO 160 Filtering Questions

Discussion in 'Amp Tech Center' started by MasterEvan07, Jul 11, 2020.

  1. MasterEvan07

    MasterEvan07 Tele-Meister

    Posts:
    342
    Joined:
    Apr 19, 2013
    Location:
    Dakotas
    Trying to return this Sano 160 to stock, as well as make it safer, for a guy and found there's some curious, and heavy, filtering with an aftermarket can cap that was installed some time ago.

    I don't have a proper ESR meter to confirm the can is bad but it's a 60/20/20/20 can and the 160R schematic (the only 160 variation I can find a schematic for) uses a 40/20/20.

    There's also a bulging old 30µF Sprague Atom that's got a node going to the PI which I'm unsure of why it's there as node B looks like it should take care of the PI, but I'm likely missing something glaringly obvious - any thoughts on it?

    [​IMG]


    [​IMG]

    [​IMG]

    [​IMG]


    [​IMG]
     
  2. Jon Snell

    Jon Snell Tele-Meister

    Posts:
    397
    Joined:
    Aug 31, 2015
    Location:
    Jurassic Coast. UK.
    If you want to return it to 'stock', replace the electrolytics like for like as they are at present and any drifted value resistors. The coupling capacitors, as far as I can see from your photos look of a reasonable type, eg; not paper or paper in oil that tend to electrically leak due to absorption of moisture.
     
  3. MasterEvan07

    MasterEvan07 Tele-Meister

    Posts:
    342
    Joined:
    Apr 19, 2013
    Location:
    Dakotas
    I’m with you, but I don’t have a certain reference point for “like for like” since the can cap is a replacement and I can’t find an exact schematic to refer to. The closest is the 160R schematic I posted here, and it assumedly appears that it’s the same, but with that grafted in reverb portion at the top. Hence my trying to suss out if there’s something I’m overlooking what with the seemingly additional Sprague filter I’ve no reference for.
     
    tubegeek likes this.
  4. tubegeek

    tubegeek Friend of Leo's

    Age:
    59
    Posts:
    2,480
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    Sometimes the best you can do is the best you can do.

    FYI: hayseedhamfest at https://hayseedhamfest.com/ is a source for a wide variety of can combinations if you want to try and put it to (what may perhaps be) the original can values. I have not purchased from them, but I plan to.

    The added Sprague may be some kind of repair attempt to fix the filter for a humming PI, just a guess.

    It looks to me like your assumption that the extra reverb circuit is the only difference is borne out by the way the 160R schematic is marked. I'd try it with 40/20/20 and see what you get.

    If you wanted to get slick maybe put the small Fender choke instead of the 2K dropping resistor, that way you'd KNOW you had good filtering for the screens, PI and preamp. That Sprague might be a hint that the 40/20/20 wasn't enough filtering in the opinion of the previous tech. Rather than piling up more uFs, spending the 20 bucks or whatever on the choke strikes me as a better solution. How's the heater wiring? Twisted? Center tapped? Elevated? Maybe some room for improvement there in the fight against hum and that's certainly a cheap thing to fix.
     
    Last edited: Jul 12, 2020
    MasterEvan07 likes this.
  5. Jon Snell

    Jon Snell Tele-Meister

    Posts:
    397
    Joined:
    Aug 31, 2015
    Location:
    Jurassic Coast. UK.
    MasterEvan07 and tubegeek like this.
  6. MasterEvan07

    MasterEvan07 Tele-Meister

    Posts:
    342
    Joined:
    Apr 19, 2013
    Location:
    Dakotas
    Heaters twisted with a CT. I'm going to do the simplest, back to stock 40/20/20 and proper grounded cable and go from there. I'm trusting it just needs to return to spec, be made safest, and will be fine.
     
    tubegeek likes this.
  7. tubegeek

    tubegeek Friend of Leo's

    Age:
    59
    Posts:
    2,480
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    Well if it isn't, the path forward will be more predictable too.

    If you get a chance to connect the heater CT at the power tubes cathode instead of ground, that can sometimes make a big difference (sometimes it doesn't but it never hurts to try.) Is the PT actually the way it shows in the schematic with a "real" center tapped heater winding?

    Oh!
    A recent thread reminded me: connect both output tubes heaters the same way, same side of the heater winding to the same pin. Then the push pull arrangement will cancel any heater hum between those two tubes. Another super easy thing to try.
     
    Last edited: Jul 12, 2020
    MasterEvan07 likes this.
  8. MasterEvan07

    MasterEvan07 Tele-Meister

    Posts:
    342
    Joined:
    Apr 19, 2013
    Location:
    Dakotas
    Very cool, thanks for the thoughts and recommendations!

    The amp is functional at the moment and has a hum that goes away after playing for a few minutes. All original tubes - Amperex 7025 x3 and GE 6BQ5s x2, diode rectified. Once the circuit is addressed I'll see if there's need for any new tubes. It sounds pretty stiff/sterile, so hopefully some relaxed (to spec) filtering will liven it up some.

    It's not really a prime guitar amp but it will suit the purpose for this guy I'm helping.
     
    tubegeek likes this.
  9. MasterEvan07

    MasterEvan07 Tele-Meister

    Posts:
    342
    Joined:
    Apr 19, 2013
    Location:
    Dakotas
    Ok, so I'm pretty positive I did this properly but I need a second, third, and so on set of eyes.

    New cap is grounded on the opposite tabs under the resistors. Bottom "D" is 40µF, the remaining are all 20µF.

    As far as I can tell it's wired back to stock now. Bottom tap is feeding the OT (schem A), left is screen grid and trem plate (schem B), top is all the preamp and PI (schem C), and left is the suppressor grid filter shown in the image below.

    New grounded cable, death cap gone. Voltage are really high though and I feel like I'm missing something.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  10. timfred

    timfred TDPRI Member

    Posts:
    93
    Joined:
    Mar 14, 2016
    Location:
    Northern CA
    Do you have tubes in? Voltages will be high until there’s load on the power supply.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.