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

5F2A Weirdness...Troubleshooting

Discussion in 'Shock Brother's DIY Amps' started by keithb7, Nov 24, 2017.

  1. The Guy

    The Guy Tele-Holic

    596
    Sep 15, 2016
    Guitarsphere
    I had a similar problem once, same fireworks... it was a preamp tube pushing too much current. Check those out.
     

  2. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    When things go from bad to worse...The voltage drop worked. Before buttoning up the amp, I take the chopstick test. Hmm. Something is up. Something on the board is chirping when I tap around. The whole board no matter where I tap. The amp works but something ain't right I tell ya. I see a small crack around the grey ceramic looking outer layer of a resistor. I get to looking and I see a another one cracked too. I test the resistors , they measured in spec. Tap some more. Bloody well, I think its these resistors! I heat up a turret to remove suspect resistor and the lead comes right out of the resistor. Broken inside. Then another one. Same thing. 1 of said resistors is NFB resistor. Hmm. Imagine that. Remember in the video on page 1 here, the arcing changed when the NFB was switched on. The next bad resistor? The 220K to ground off 6V6 pin 5. That would be the grid resistor. Imagine if that resistor were shorting out, what that might do to add to to power tube arcing? The dang resistors measured good when tested with my DMM. Intermittent problems. Yes sir, they'll drive ya mad. Well a home amp hack anyway.

    These resistors are some type of older resistor that I picked up somewhere. They don't like heat much I reckon. Remember I said I built this amp a while ago? It was 2010. New in my amp phase. I am guessing I cooked these when I built the amp. They lasted 7.5 years and the problems began. Today, I can only blame the builder.

    The good news is the 6V6 will be running at a nice lower voltage. The wiring got cleaned up. We added a 470R 5W screen resistor to keep a cool head. Now we get to install new resistors. And the best part? One of my turrets popped out of the board when I was lifting off a resistor. Life is sure hard when you're dumb and trying to get through it. Lol.
     
    Last edited: Nov 29, 2017
    King Fan, Axis29 and jsnwhite619 like this.

  3. jsnwhite619

    jsnwhite619 Tele-Afflicted Ad Free Member

    Sep 10, 2013
    Georgia
    Well cheers in seeing those cracks. Could have been a much longer haul if you hadn't noticed them.

    I'm amazed that the diodes worked so well. It's crazy how the whole system works - the center tap is grounded to the chassis, and you can touch the chassis, but adding the diodes between that CT and ground dropped, what, 80v off you B+? It still just amazes me sometimes how things work.
     
    King Fan likes this.

  4. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    Well would you look a' that...Just look at the culprits here. I was tapping and tapping. Listening. I know I’ve heard something like this before. Tap-tap...Tap-tap...I a see the crack. My internal light bulb limiter went real bright.

    What are these? Wire wound type?

    [​IMG]
     
    Last edited: Nov 30, 2017
    Axis29 likes this.

  5. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia
    Sounds like the amp got played a lot
     

  6. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    Yes. On 10. :)
     

  7. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia
    That's a good thing
     

  8. Mr Ridesglide

    Mr Ridesglide Tele-Afflicted Silver Supporter

    Dec 11, 2009
    Bloomington, MN

  9. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    Tap 'em lightly with a hammer, you'll see if there's a wire element inside. Strange to see 4 at once fail in the same way.
     

  10. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    Humbly, I'm looking for ideas tonight. I've worked myself into a frustrated state.

    Above mentioned resistors replaced. When I fire up the amp now, the amp makes noise with a guitar but it's quiet. It almost sounds like the OT signal is grounded or something. I have been racking my brain for hours over this symptom. Trying different things to no avail. I have got myself worked stupid over it and need to take a break and a fresh new look after a rest.

    I've tried swapping in known good tubes. All except rectifier. Left in so far as I am making good steady B+.
    Lifted board several times to look underneath and inspect & check wiring
    Checked and rechecked all my wiring against layout wiring many, many times. Visual and continuity checks with DMM.
    I replaced the 2 coupling caps and the 2 cathode caps.
    Checked all my contacts for grounds or not, as required.
    Lifted board and ran amp to ensure nothing underneath is possibly making ground contact. No improvement.
    I have tried different speakers and cords and guitars to eliminate those variables.
    Chopstick entire circuit when on, it's all nice and quiet now.
    The switchable NFB: I hear a little crackle when I switch it on and off. Same as before. I also removed NFB completely to eliminate that option. No improvement.
    Tone and volume knobs work as they should. Just the amp is quiet. It breaks up, as I crank the volume, like it used to. It just puts out what sounds like about 1/4 of a watt of power.

    Next I was thinking I'd take voltages and post. Tomorrow maybe. I think I need a break for a bit. Sleep on it.
    Maybe put it away until Monday with fresh eyes and start over.

    Tips are appreciated. Thanks, Keith
     
    Last edited: Dec 1, 2017

  11. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Oof. Total bummer. Ow.

    I’m not usually the guy to figure anything out, but new resistors in several places remind me that you should triple check all their values. Says the guy who put a 470K instead of a 470R.
     
    clintj likes this.

  12. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    This. Voltages, and verify values by meter. It's probably something simple, but it's easy to get too involved. Step back for a bit, and look at it when you're fresh.

    Oh, and a 330k looks a heck of a lot like a 3.3M. Just sayin' ;-)
     

  13. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    Thanks guys. Will do later. Have you ever been worked to frustration?

    I stubbornly plowed on without pulling out the schematic nor measuring voltages up to this point. I had only swapped in some simple parts and the amp made plenty of noise before. I figured “I got this”. :lol:

    Alas, its beating me up. Lol.
    Yes probably something simple. Hard to see through the fog of war when your frustrated. Your support is appreciated.
     

  14. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia
    Good luck and I am sure that you will be able to shake it out with a complete set of voltages.




    I think a good voltage chart looks like this



    Pin 1 ?

    Pin 2 heater ________

    Pin 3 plate ________

    Pin 4 screen ________

    Pin 5 grid _________

    Pin 6 screen res _______

    Pin 7 heater _______




    I find the voltage charts are so much more readable if the name with the pin is included, like plate
     

  15. jsnwhite619

    jsnwhite619 Tele-Afflicted Ad Free Member

    Sep 10, 2013
    Georgia
    I've been racking my brain because I've had the same symptoms in a build before - the 5F4 Super I did a while back. Like you said, everything worked like it should have, but it sounded like you were listening to a headphone/line out signal. Definitely not what a 2x6L6 Fender should be doing. Finally found it after a week of going over it with my continuity tester. I had crossed and accidentally swapped two leads on V2 - maybe pins 2 & 3, I can't really remember - but that was it. With all the parts swapping you've done on this one, it might be something to check.
     
    keithb7 likes this.

  16. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Here's some encouragement:

    - You very, very likely know enough to fix this. It's not some crazy, weird problem that will require an exorcist.

    - You do know what you're doing. It's not your fault or something for fooling with it too much. Machines, I think, come to have a will of their own.

    - You are very often encouraging to others when they get zeroed-in and in a funk because they can't solve something. Try not to be too hard on yourself.

    - Go play some of your other awesome amps for a while to remind yourself how good you are at building these things and how good you are at repairing them. This one issue at the moment should not define the way you think of yourself vis-a-vis all amps for all time.

    - Back away from working on it until it doesn't stress you out. Then start again afresh with an approach that is not coupled with stress. When I get super-stressed, my tendency is to plow through it and fix it (damn it!), but that normally makes everything worse.

    - You'll get it. You have time. It's not like you're under the gun with a deadline for a customer.

    - Go play music for a while and remind yourself what you love about all this rather than thinking about what is frustrating.
     

  17. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    I've totally worked to the point of anger before. Go take a walk if it isn't snowing, and relax. Heck, even if it is snowing go for it. It's peaceful to watch the flakes as long as you don't have to shovel them.

    I've had to flip a chassis and layout diagram 180° before to force myself to look at it as if it's a complete unknown. Totally trapped in the "I checked it as I went, it has to be right" mindset.

    I can't remember from past conversations, but do you have a scope? If not, a DMM is useful. It will show you the AC voltage at each tube grid so you can quickly check gain staging. I've used mine to do a quick go/no-go check of pickups and such before out in the field.
     

  18. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia
    Amp vital signs


    Healthy plate voltage
    Robust bias voltage to deal with the healthy plate voltage
    Strong signal to work against the robust bias voltage.




    Also, I think it's good to know the resistance of the OT primary ahead of time, so if something like this happens you can quickly verify that the OT is good. The secondary could also be measured, but it is way less important.
     
    magic smoke likes this.

  19. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    LOL! Don't you remember me going back and forth with my Twin a little while ago? Metering all the components made the difference for me. I was swearing I'd done it right and put the right resistor in that place.

    As much help and encouragement as you were to me, I know I won;'t be much help, but I will encourage! You got this.


    And, yes, I have gotten tot he point of losing my temper and wanting to throw stuff... Usually it involves plumbing. Actually, after several plumbing repairs, I've had to make wrench size drywall repairs. And, normally I'm the most laid back dude you'd ever know.
     
    magic smoke and keithb7 like this.

  20. Mr Ridesglide

    Mr Ridesglide Tele-Afflicted Silver Supporter

    Dec 11, 2009
    Bloomington, MN
    Oh boy. After this week I can feel the pain! Hang in there.
     

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