Results 1 to 18 of 18

Thread: 5e3 Troubleshooting

  1. #1
    Junior Member
    Join Date
    Jan 2011
    Posts
    16

    5e3 Troubleshooting

    I finished my 2nd 5e3 build and just can't get it going. Initially, only one channel worked. I traced everything, couldn't find it. Pulled the circuit out, re-wired, and now both channels work... Well, in theory. I am hearing signal from my guitar out of 1&2 B&N it just sounds like a bad fuzz pedal. The sound is low volume, but there is input. I tried different power/pre amp tubes and the same thing happened.
    I need some kind and wise elder to talk me through the basics of taking readings. I just got a sweet new meter, but really don't know how to use it correctly.

    I tried to take some readings and fried the 100ohm resistors from the pilot light
    That was dumb. I replaced them, but now I am back to square one.

    I am at the place where I am ready to learn from this frustrating build but I am at the limit of my experience. All of the previous posts have been insightful, just not quite my situation.

    My current theory is that it is either the OT or the Rectifier tube (two things I haven't swapped out). The fact is, before I go replacing stuff I need to learn how to meter. I have done continuity checks on every connection. That was a no-brainer.

    I am using the schematic Mojo provides in their small-parts kit.

    Help!

  2. #2
    Supporting Member txstrat's Avatar
    Join Date
    Mar 2008
    Location
    Germany
    Posts
    1,237
    I think it's unlikely to be the OT or recto tube since the amp had worked before (at least one channel).
    It might be a wrong or missing wiring. Could you post some pics of your build?
    To measure your voltages put the black probe of the meter to ground and the red to the spot you want to measure.
    Set the meter right (AC, DC, OHMS).
    Be aware, the voltages in tube amps can KILL you.

  3. #3
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    Thanks. Here are some pictures:
    photo-2.jpgphoto-3.jpgphoto-4.jpg

  4. #4
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    And a few more...
    Attached Thumbnails Attached Thumbnails photo-5.jpg   photo-6.jpg   photo-7.jpg   photo-8.jpg  

  5. #5
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    Okay, this will sound dumb, but I am measuring DC voltages on the pins of V1-5. Am I attaching the leads to the meter at 10A or CxmA (200mA)? Obviously COM is ground. But what is V Omega? Is that for resistance measurements?

    Also, these measurements on V1-5. Are they taken with the standby switch on or off?
    I know, I know: this is real basic and I should know, but I am trying to be careful and learn!

    meter.jpg

  6. #6
    Supporting Member txstrat's Avatar
    Join Date
    Mar 2008
    Location
    Germany
    Posts
    1,237
    Right, COM is ground (or COMmon). The red one on the right is for Voltage and Ohms (the omega sign stands for ohms). Use the 1000v setting on DC while measuring inside the circuit (after the rectifier). While measuring the transformer leads (before the rectifier) set in on AC. For the heaters you use the AC setting too (you could set it on 20v to get a more exact reading).
    The amp has to be in play mode (stand by in ON position) - otherwise there would be just the heaters voltages on the tube pins.
    Search through this forum to get an idea what the voltages in a 5E3 should read (I've seen several threads with them voltages listed).
    Your build looks quite tidy and on first glance I can't make out anything obviously wrong.
    Do the tubes glow?
    Look for accidentally wrong connections.
    Maybe the shielded wire was too hot soldered and the isolation melted - leading to a short (just a shot in the dark).
    Compare every solder joint with the schematic (make a copy and take a pencil to cross out every checked connection).
    More ideas might come up when you post the voltage readings.
    (maybe you could use alligator clips on your meter probes -to avoid slipping- and switch the std by in ON position when you clipped them in place)
    Good luck and be careful.

  7. #7
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    Thanks for the tips. I was able to measure everything. Here are the readings:

    pin: 1 2 3 4 5 6 7 8 9
    V1 12ax7: 208 1.64 3.37------ 206 1.63 3.37
    V2 12ax7: 201 1.54 3.37------ 306 5 3.37
    V3 6v6GT: 3.37 394 379 3.37 26
    V3 6v6GT: 3.37 396 380 3.37 26
    V5 5y3GT: 117 393 392 117

  8. #8
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    Sorry, that didn't come out looking as cool as the way I typed it!

  9. #9
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    Here it is better organized:
    V1 12ax7:
    Pin 1: 208
    Pin 3: 1.64
    Pins 4-5: 3.37
    Pin 6: 206
    Pin 8: 1.63
    Pin 9: 3.37

    V2 12ax7:
    Pin 1: 201
    Pin 3: 1.54
    Pins 4-5: 3.37
    Pin 6: 306
    Pin 8: 5
    Pin 9: 3.37

    V3 6v6GT:
    Pin 2: 3.37
    Pin 3: 394
    Pin 4: 379
    Pin 7: 3.37
    Pin 8: 26

    V4 6v6GT:
    Pin 2: 3.37
    Pin 3: 396
    Pin 4: 380
    Pin 7: 3.37
    Pin 8: 26

    V5 5y3GT:
    Pin 2: 117
    Pin 4: 393
    Pin 6: 392
    Pin 8: 117

  10. #10
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    I just re-measured the Rectifier because 117 ain't right for sure! Here is what I read this time:
    V5 5y3GT:
    Pin 2: 8
    Pin 4: 393
    Pin 6: 392
    Pin 8: 8

    I'm not sure how I got 117 before! Although 117 is a familiar voltage! According to the Mojo transformer schematic, it should be 5v ac.

  11. #11
    Supporting Member txstrat's Avatar
    Join Date
    Mar 2008
    Location
    Germany
    Posts
    1,237
    What about pins 3 and 7 on tubes 1 and 2?

  12. #12
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    I will have to take a look this afternoon. I was reading a chart that didn't give voltage for pin 7 on tubes 1 & 2 so I didn't measure them. I got that chart off the web and nearly all of the voltages were lower than anything that I was reading.

    Pin 3 was 1.64 on V1 and 1.54 on V2

  13. #13
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    Okay, I built a jumper with clips on each end and a 2w 470ohm resister inline to drain the caps. I have read several different approaches here, I was wondering:
    What mV reading is safe? For instance, I connected each cap (positive side), waited, and re-measured. They still don't read 0.00. Right now they read 5.0 mV.

    Should I reconnect them one by one and wait longer until it reads 0.0? Or should I try another method like grounding pin 1 of a pre-amp tube and waiting?

  14. #14
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    Here is something that I noticed doing continuity checks. When I ground one probe and then touch the speaker tip, I get the continuity alarm. Is my OT to speaker correct?ot-speaker.jpg

  15. #15
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    I just finished resistance checks on the input wiring that Loudthud posted in another thread:

    "With power off and no cable plugged in, the grid of the tube (pin 2 or 7) should measure 34K to ground. With an open ended cable plugged into the #1 input you should measure 1.034Meg. With the cable in the #2 input you should measure 68K. Next measure from the end of the cable where it plugs into the guitar. The #1 input should measure 1Meg between tip and ground. The #2 input should measure 136K. Now measure between the tip of the cable and the grid pin on the tube socket. 34K on the #1 input and 68K on the #2 input. Measure both channels."

    Everything checks out in both channels so I think I can rule out the input jack wiring. Any other suggestions?

  16. #16
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    Alright! I found that I missed the 1.5K resistor on the tag board. I just forgot it! So I wired it in and it works!!!

    Phew! Thanks for answering my dumb questions and giving me a little confidence to forge ahead.

    Now I need to do some forum research on here to debug it. When I turn the tone pot up all the way it shrieks horribly. Turn it down and it sounds great.
    But that is a HUGE improvement over no volume at all!

  17. #17
    Supporting Member txstrat's Avatar
    Join Date
    Mar 2008
    Location
    Germany
    Posts
    1,237
    Great to hear that it works. Well done.
    Regarding the shrieking: if the amp had a negative feedback, I'd say interchange the wires to the power tube plates. But a standard 5E3 don't have a NFB.
    Might be the lead dress.
    Take a wooden stick (chopstick) and move the wires inside the chassis around. Any changes?
    Look if you could shorten the grid wires (of any tube) or move the 1.5K grid stopper resistors (to the power tubes pins 5) from the board directly to the tube sockets.

  18. #18
    Junior Member
    Join Date
    Jan 2011
    Posts
    16
    I'll have to get into it in the morning. Thanks again!

    I have moved this thread to:
    5e3 Feedback when tone pot is turned up

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. transistor troubleshooting
    By trem in forum Maintenance, Troubleshooting & Repair
    Replies: 2
    Last Post: 09-28-2010, 04:17 PM
  2. RAT Troubleshooting
    By ManRay in forum Guitar Effects
    Replies: 2
    Last Post: 08-11-2010, 02:21 PM
  3. Replies: 7
    Last Post: 06-26-2009, 06:24 AM
  4. Troubleshooting motorboating
    By EETStudent in forum Maintenance, Troubleshooting & Repair
    Replies: 1
    Last Post: 04-23-2008, 11:17 PM
  5. 6g15 troubleshooting
    By joelw in forum Guitar Effects
    Replies: 2
    Last Post: 03-25-2008, 06:42 AM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •