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5G9 Tremolux build troubleshooting

Discussion in 'Shock Brother's DIY Amps' started by montana, Feb 2, 2019.

  1. montana

    montana TDPRI Member

    69
    May 5, 2003
    Seattle
    Hey all, I fired up a new 5G9 build and encountered some puzzling issues that I'm hoping some of you more experienced builders could help me with. Voltage numbers appear a little high but within reason. The issues are:

    1) Moderately loud hum on startup, that quickly fades to a low level hum. This is without anything plugged into the input jacks.

    2) With guitar plugged in, the bright channel barely passes a signal. The normal channel passes signal but the volume pot is silent up until 2 then suddenly goes to approx 3/4 of full volume.

    3) With the somewhat working normal channel, it has a bad distorted tone. When playing a single guitar note there is an effect to the sound like a super fast tremolo— not like what I’ve understood as motorboating, but more like when you talk into a fan and it sounds like a robot :) This is at any volume.

    4) The circuit board is very microphonic when tapped. Louder near the preamp area.

    Things I’ve checked or tried:

    • I’ve gone back through touch up soldering on all eyelets.

    • Depth and speed of tremolo circuit sounds like it’s working ok.

    • Tone pot seems ineffective.

    • I’ve swapped out V1 and V2 with different tubes with no change to the problem.

    • Confirmed good resistance values between the 4 input jacks and V1 tube pins.

    • That capacitor connected to pin 2 of V2 and the volume pot pops very loud when measuring voltage on it. Swapping this cap out made no difference. And pin 2 of V2 is very sound sensitive and pops/cracks when tapping it with a chopstick.

    • I built it as a clone, so grounded the filter caps to their cover. Tried rerouting the ground to the rest of the power section grounding point to see if it made any difference in hum, but it didn’t.

    • Tried different speakers

    Sharing some photos and voltages for context. Any suggestions on what else I could try to solve this would be appreciated.

    Screen Shot 2019-02-02 at 10.48.44 AM.png IMG_1342.JPG IMG_1343.JPG IMG_1350.JPG
     
  2. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Pretty build -- deserves to work!

    I can't be much help, but a few random ideas here.

    You say you tested resistance from input jacks to V1. Did you do this connecting to the tabs of a plug in the jack? Those 4-plex input farms are famously tricky to wire cleanly, and then Switchcraft jacks have a fairly common issue where the shunting prong doesn't open all the way -- sometimes even with one ¼ plug and not another.

    You get a loud pop on V2 p2? Do you get a loud pop on V1 p2? V1 p7? Should be louder to probe the grids (signal) earlier in the amp cuz more amplification downstream. Does anyone think some of your other notes hint we may be dealing with a problem between V1 and V2?

    Microphonic in my limited experience has been tubes -- even when the whole chassis or whole amp seems microphonic and tube tapping doesn't 'ring a bell.' Did you try known-good new tubes in V1 and V2? Don't exempt the other tubes either. If all new tubes don't fix it, I guess I'd maybe suspect the tube pins / sockets? Maybe somebody else knows other causes of microphonics.

    Without dissecting the voltages, have you compared resistances from the schematic (amp off) from the grids and cathodes to ground? You can also confirm that plates are correctly connected to the proper B+ nodes.

    I'm sure the cool kids will get here soon and chime in with more help. I'll say in closing your tests so far show method and thought that also deserve to be rewarded.
     
  3. tubeswell

    tubeswell Friend of Leo's

    Jul 1, 2008
    NZ
    IMG_1350.JPG

    'Grounding' the filter caps like ^that^ is not grounding them properly. That is not how a clone is supposed to look. In a stock tweed tremolux (and any similar fender amp with filter caps in a doghouse outside the chassis), the filter caps are mounted on an eyelet board firmly secured to the back of the chassis. The doghouse cover is only a cover and does not carry any electrical return current. You need separate wires from each filter cap ground return lead back to the rest of the amp and a proper grounding scheme.

    Before you turn it on again, mount the filter caps on a proper eyelet or turret board
     
    Last edited: Feb 2, 2019
  4. mpassell

    mpassell TDPRI Member Platinum Supporter

    45
    Sep 26, 2011
    San Francisco CA
    It's hard to see where the pre-amp ground bus gets to its final ground point. I suggest grounding it on the input jack side of the chassis.
     
    boredguy6060 likes this.
  5. montana

    montana TDPRI Member

    69
    May 5, 2003
    Seattle
    Very much appreciate the input guys,

    The preamp section is grounded to the top right input jack.

    I measured the input jacks from tip of instrument cable to pins 2 and 7 of V1 depending on input, and they check out right. And mechanically they appear to be fine when plugging into each of them. I also went and swapped my V1 and V2 tubes out again with other known good tubes—no change. So if all is ok up until V1, including the tube, it makes me wonder if it’s the tube socket like King Fan suggests. Or volume pot(s)?

    I’ve triple checked the wiring and the voltages, but I feel I must still be missing something. The voltages (although a bit high like 402 for B+) are not way off of the schematic.

    My intent was to ground the filter caps to the doghouse like Fender did on some early tweeds like the Bassman and 5G9 Tremolux for aesthetic reasons, just for this one build, but change it if it didn’t work. When I thought it might be the cause of hum I disconnected the doghouse with caps from the chassis and grounded it at the power section ground and it made zero difference in hum.
     
  6. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    It sounds like the amp is oscillating. Pull V3 to kill the tremolo circuit and see if that affects the noise. Have you tried another set of power tubes?

    [​IMG]
     
  7. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Do you have a 6.3vac heater center tap?

    More pictures... Straight on, but not too close up, so we can follow wires. Like three from right to left showing inputs, vvt, trem, pilot and switch. Then the board same 3 sections, then the tube sockets. More eyes=more better.
     
    King Fan likes this.
  8. montana

    montana TDPRI Member

    69
    May 5, 2003
    Seattle
    Pulling V3 was a great idea. Really was hoping it would isolate the issue, unfortunately the oscillating sound persisted exactly the same.

    Swapped power tubes for another known good pair, but unchanged.

    My heaters are reading 6.43vac. I'm using an artificial center tap grounded with 100 ohm resistors on V4.

    Adding more photos as suggested...

    IMG_1364.JPG IMG_1365.JPG IMG_1371.JPG IMG_1367.JPG IMG_1368.JPG IMG_1369.JPG IMG_1370.JPG
     
  9. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    OK, that mirror-finish chassis is messing with my already-limited ability to trace wires. :) Side note: Looks awesome. What kind / where'd you get it?

    While the sharp eyes here trace the wiring, though, I've had good luck with an audio signal trace in this setting. (Did we ever hear the results of a complete left to right grid-tap test or 'pop test'? More primitive but way easy.)
     
    Snfoilhat likes this.
  10. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Double post, forum seems to be at a crawl again.
     
  11. montana

    montana TDPRI Member

    69
    May 5, 2003
    Seattle
    Got the chassis from Weber. They finally did another run of Super chassis labeled for a Tremolux. I've been wanting to build one for quite awhile so jumped on it!

    Did the “pop” test like @King Fan suggested—could be a clue to what’s going on—because pins 1 and 2 on V1 make an expected pop sound but pins 6 and 7 are very very subtle with volume all the way up. That aligns with the super low output of that channel. So does that mean the issue would be something in the signal path after V1? I checked my wiring from the board through the volume and tone pots again (referencing Fender 5G9 layout) and it appears right. Unless the cap values I chose are wrong...

    IMG_1380.JPG IMG_1381.JPG

    Also Pin 2 (grid) on V2 (phase inverter) pops crazy loud compared to all other pins. Loud as if the amp is at full volume even with the volumes all the way down. That seems suspicious.
     
  12. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    V2 P2 is downstream of volume and tone control so they will not have effect on the pop there. That sounds good.

    That super shiny reflective chassis makes it a task to trace the circuit. I would take a fresh layout drawing and a highlighter. Go over each individual wire on the layout and say outloud where the wire starts and ends then compare that to your build. Confirm it at least twice. Then highlight the wire on the layout and move to the next. Its easy to overlook something youve been staring at for a week.

    Hows the humm? I would be chopsticking all those parallel wires around the tube sockets. The illusion of the chassis likely makes it look worse than reality!

    Edit to say... You might try turning off your flash(if using it)when taking photos.
     
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  13. flyswatter

    flyswatter Friend of Leo's

    Jan 12, 2013
    Quebec
    You might need to ground the FCs for the preamp to the preamp bus (which ideally should be grounded one end only, finishing at the grounding lug for an input jack), separately from the reservoir cap, etc. that should ground to the power supply star. I built a 6G3 Brownface Deluxe (which is more tweed Tremoluxy than Deluxey) "vintage correct" that hummed like crazy until I changed the doghouse grounding scheme -- then was perfect. I did a thread on Shock Brothers -- it's post #6 on this thread: http://www.tdpri.com/threads/my-6g3-brown-deluxe-build.913632/

    I concur with "tubeswell" that those fliter caps really need to be on an eyelet or turret board. The problem is that if they bend down and touch the chassis and the amp is accidentally on an ungrounded circuit (like an old house or somebody uses a dollar store extension cord) you end up with 400 volts live on the chassis.
     
    Last edited: Feb 4, 2019
  14. dan40

    dan40 Tele-Afflicted Silver Supporter

    Aug 19, 2015
    Richmond Va
    The pops when probing with your meter are perfectly normal but the hum and extra microphonic issues you are hearing may indicate a faulty solder joint in the preamp. Have you reflowed all joints and grounding points? A full set of DC voltages at all tube sockets would also help narrow things down.
     
    trouserpress likes this.
  15. montana

    montana TDPRI Member

    69
    May 5, 2003
    Seattle
    Retraced wiring twice with highlighter and layout as recommended. My eyes are getting buggy, but everything appears right.

    I've reflowed nearly every eyelet, but haven't done that to the tube sockets, which I will do next.

    The amp consistently produces a 4 second wave of loud hum when the tubes get warmed up, then fades to a low level hum. Not terribly bad, but when compared to my other very quite tweed builds, it's noticeable. I will unground the filter caps from the cover and try running a single ground wire off the filters to the power supply ground, and if that doesn't help I'll try the preamp ground bus.

    Thanks for hanging in there with me fellas.
     
  16. montana

    montana TDPRI Member

    69
    May 5, 2003
    Seattle
    Ok, had a chance to switched up the grounding on the filter caps to the power supply ground point, but no change in hum. Then tried the pre amp ground point and hum was worse, so put it back at the power supply grounding point. Reflowing the solder of the tube sockets and pots unlocked the signal path in the bright channel and now that and the tone pot seems to be working proper. Hooray!

    I also when through the lead dress and moved the wires around quite a bit with a chopstick but that didn't create any noticeable changes to hum or distorted tone.

    Still getting a surge of hum at startup that mellows out a bit and the nasally oscillating sound. I recorded a video to illustrate...
    1) Power up with surge of hum that quiets but is still present.
    2) Volume down, tapping circuit board
    3) Volume up (instrument cable plugged in), tapping circuit board = microphonic
    4) Plug cable into guitar
    5) Distorted oscillating sound



    One other thing I haven't tried is swapping the rectifier tube for another known good one. Maybe?

    I also started to suspect if I wired the output transformer correctly. I have the orange wire going to B+, green and brown going to the plates (pin 3) of the 6V6's. There's only one wire (yellow) on the secondary wired up to the speaker jack. There was no "COM" on the transformer so I'm assuming the transformer is self grounded to the chassis. Is that correct?

    IMG_1387.JPG
     
  17. dan40

    dan40 Tele-Afflicted Silver Supporter

    Aug 19, 2015
    Richmond Va
    There are alot of wires bunched into one area that may be causing an oscillation. It may be wise to shorten the leads as much as possible leading to the sockets and pots. Anywhere the plate leads cross a cathode or grid lead, it should do so at a right angle. I like to lay my plate leads against the chassis and run the others up off of the chassis. Those tweed chassis are very cramped so lead dress can be very important.

    Before going to all of that trouble, you should get a full set of DC voltages at all pins and also check AC voltages at the filament connections. This will really help to narrow things down.
     
  18. dan40

    dan40 Tele-Afflicted Silver Supporter

    Aug 19, 2015
    Richmond Va
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  19. trouserpress

    trouserpress Tele-Meister

    Age:
    55
    498
    May 4, 2015
    Leipzig
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  20. montana

    montana TDPRI Member

    69
    May 5, 2003
    Seattle
    Thanks @dan40. I did move those leads around quite a bit to check for any changes but didn’t have any luck. I generally have just made sure all the yellow DC wires cross the AC heaters at 90 degrees. Are there any other best practices for how they should or should not interact?

    Here are my voltages listed out:

    Heaters = 6.47vac

    V1 12AY7
    Pin 1-plate = 175
    Pin 2-grid = 0
    Pin 3 & 8-cath =2.8
    pin 6-plate = 177
    Pin 7-grid = 0

    V2 12AX7 (phase inverter)
    Pin 1-plate = 217
    Pin 2-grid = 18
    Pin 3 & 8-cath =28
    pin 6-plate = 217
    Pin 7-grid = 19

    V3 12AX7 (tremolo)
    Pin 1-plate = 265
    Pin 2-grid = 0
    Pin 3-cath = 2
    Pin 6-plate = 396
    Pin 7-grid = 265
    Pin 8-cath = 267

    V4 6V6
    Pin 3-plate = 388
    Pin 4-grid = 396
    Pin 5-grid= -27
    Pin 8-cath= 3

    V5 6V6
    Pin 3-plate = 388
    Pin 4-grid = 396
    Pin 5-grid= -27
    Pin 8-cath= 3

    V6 5U4
    Pin 2 =402
    Pin 4 = 338 AC
    Pin 6 = 338 AC
    Pin 8 = 402
     
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