Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups darrenriley.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Tonemaster Troubadour 214 (Magnatone 213) - Help diagnosing crackling

Discussion in 'Amp Tech Center' started by GoKart Mozart, Aug 4, 2018.

  1. GoKart Mozart

    GoKart Mozart TDPRI Member

    81
    Aug 30, 2012
    Killen, AL
    This is kind of a "part 2" to a previous thread I started last month. I recently got a Tonemaster 214 in a trade. I put in a 3 prong cord, removed the death cap, and replaced the filter cap can with a new one from CE Manufacturing. When I got the amp, it had some static/crackling and I was hoping that replacing the electrolytics would help but unfortunately it has not.

    [​IMG]

    [​IMG]

    [​IMG]

    When I got the amp, it had the original Telefunken 12AX7s, GE 12AU7, Sylvania 6V6s, and GE 5Y3. I thought I had some of the static/crackling isolated to the 12AU7 so I replaced it with a NOS GE tube but it really didn't help any. I've swapped around all of the tubes with ones from other amps and the crackling is still there.

    Here's a video.


    I've cleaned the tube sockets but that hasn't helped any. Is there a "right" way to troubleshoot an annoyance like this?
     
    LarryBudMelman likes this.

  2. GoKart Mozart

    GoKart Mozart TDPRI Member

    81
    Aug 30, 2012
    Killen, AL
    Forgot to post this; this is the closest schematic I've been able to find. This was a later evolution (Magnatone model 413) that replaced the 12AX7 oscillator with a 6AV6 and added some tone switches in the preamp. Other than those changes, I believe it's identical to mine:
    http://www.magnatoneamps.com/schematics/magnatone_413.png
     

  3. Nickfl

    Nickfl Tele-Holic

    990
    May 24, 2016
    Florida
    At this point I'd suspect a leaky coupling cap. See if you have some DC voltage on the pots or somewhere else you shouldn't.
     
    LarryBudMelman likes this.

  4. GoKart Mozart

    GoKart Mozart TDPRI Member

    81
    Aug 30, 2012
    Killen, AL
    I checked them and the only one showing DC voltage is the coupling cap going from the V1 plate to the channel A volume pot (measuring at the lead going to the pot). I had to set my meter to the lowest DC setting; it’s jumping around between -20mV and 20mV.

    Seems small but none of the other coupling caps appear to be letting even that small amount of voltage through. Could this be it?

    Thanks!
     

  5. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia
    Crackling is a bad connection.
     
    LarryBudMelman likes this.

  6. corliss1

    corliss1 Friend of Leo's Gold Supporter

    Sep 13, 2008
    Lansing, MI
    The "right" way is to use a signal tracer to check various points of the amp, sending the signal out to your test amp. When you find where the crackle noise starts you've located the component or area of the issue.

    I would bet on plate resistors causing this noise as that is the classic "bacon frying" sound of old plate resistors.
     
    Nickfl and LarryBudMelman like this.

  7. LarryBudMelman

    LarryBudMelman TDPRI Member

    Age:
    99
    40
    Jul 26, 2018
    South.
    Do what the gurus say first, (Im far from that ;) ) But I have found a few bad parts/connections with the chopstick test. Its not very scientific.
     

  8. GoKart Mozart

    GoKart Mozart TDPRI Member

    81
    Aug 30, 2012
    Killen, AL
    Thanks for the tip! So even if they’re old and causing the crackling, will they still measure the proper resistance?
     

  9. corliss1

    corliss1 Friend of Leo's Gold Supporter

    Sep 13, 2008
    Lansing, MI
    Yup - resistance will still measure fine and everything will "work" - just you have that noise.
     
    GoKart Mozart likes this.

  10. wanderin kind

    wanderin kind Tele-Meister

    Age:
    63
    137
    Apr 24, 2018
    Olympia WA
    does it sound like bacon cooking or microwave popcorn? (dang, now i'm hungry, bacon and popcorn, never tried that combo,)

    if bacon, then change out the plate resistors and you should be good. they absorb moisture and will get noisier over time.
     

  11. GoKart Mozart

    GoKart Mozart TDPRI Member

    81
    Aug 30, 2012
    Killen, AL
    I ordered some resistors and replaced the plate resistors on the first two preamp tubes but unfortunately that didn’t fix it. I was hoping I wouldn’t have to dive into the other two preamp tubes since they control the vibrato circuit and it’s a big mess o’ stuff all around those pins. Haha
    I’ve got a few more parts that I’m going to have to order for those, so more to follow.

    All of the resistors on the input jacks are carbon comp and I’m REALLY hoping I won’t have to resort to replacing those.
     

  12. GoKart Mozart

    GoKart Mozart TDPRI Member

    81
    Aug 30, 2012
    Killen, AL
    Also, I replaced the carbon film screen grid resistors on the power tubes. The cathode resistor gets REALLY hot (one of those old blocky ceramic ones) and I thought that maybe it being right on top of the screen grids could’ve cooked them but replacing them didn’t help any.
    It got me thinking though, might the cathode resistor be the cause of the crackle?

    Cathode resistor is in the top left corner:
    [​IMG]
     

  13. corliss1

    corliss1 Friend of Leo's Gold Supporter

    Sep 13, 2008
    Lansing, MI
    <cough>signal tracer<cough>

    But really, that's the right way to go about this. Without doing that you're just sorta guessing at parts, swapping them out, and hoping that's the fix. You might get lucky, or you might replace every part in the amp.
     
    Nickfl and GoKart Mozart like this.

  14. GoKart Mozart

    GoKart Mozart TDPRI Member

    81
    Aug 30, 2012
    Killen, AL
    Crap...you’re probably right. Do you have any low budget signal tracer recommendations?
     

  15. corliss1

    corliss1 Friend of Leo's Gold Supporter

    Sep 13, 2008
    Lansing, MI
    One capacitor and a cut off guitar cord. Google how to make one.

    I should just write an article on my own site since I link this a lot but I don't like it...

    http://musicfromouterspace.com/analogsynth_new/HOT_TIPS/ampsignaltracer.html

    Do that, skip the resistors. You can even skip the alligator clips and use the one end of the cap as the probe. Get in the habit of touching it to the chassis after each test to discharge it - the cap is there to keep DC from going out into your test amp.
     

  16. GoKart Mozart

    GoKart Mozart TDPRI Member

    81
    Aug 30, 2012
    Killen, AL
    Ah, interesting. So this doohickey goes into a separate amp than the one I’m actually working on, correct? Then I just run some kind of audio signal into the input of the amp being worked on?
     

  17. corliss1

    corliss1 Friend of Leo's Gold Supporter

    Sep 13, 2008
    Lansing, MI
    This takes the signal from your amp under test and sends out the specific point you probe to another amp so you can listen.

    Since you're listening for noise you wouldn't need to have a signal in the amp under test - you just want to find the noise and don't care about the "good" audio over it.

    It may also be helpful to plug the amp under test into a dummy load so you don't hear the noise in two places.
     
    GoKart Mozart likes this.

  18. GoKart Mozart

    GoKart Mozart TDPRI Member

    81
    Aug 30, 2012
    Killen, AL
    Sweet, thanks for the tip at the end! I’ve got a UA Ox that I can use as a load and mute the output.
     

IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.