Announcement

Collapse
No announcement yet.

Having a hard time debugging this one...

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Having a hard time debugging this one...

    One time only, for a good friend who's building me a Tele in trade, I'm doing a copy of a Jim Kelley Single Channel Reverb head. Started on it a long time ago and just got around to finishing the wiring on it. The problem I'm having is no sound. There's an occasional bump on the speaker while probing the power tube pins but otherwise not a sound.

    I'm testing it in 30w mode (2 center power tubes only) and without a reverb tank attached.

    I've gone over the layout and wiring several times and did find a couple mistakes an corrected them. But still no sound.

    note: during initial start up a meter probe shorted a power tube plate to its heater pin momentarily. It shined a small bright light for a moment and blew the B+ fuse at the same time I was able to reach for and disconnect power. Doesn't seem to have affected the B+ but the heater circuit is running at 5.9vac(virtual CT in place -- 2 100ohm resistors to ground). I didn't get a heater voltage reading before the short occurred so I don't know if that caused any damage to the heater windings. Resistance on the OT primary is 90 ohms and 45 ohms each between the center of the primary and each outside lead, so the OT seems normal the best I can tell.

    Voltages all seem normal except for the plate voltage to V1b is rather low.. gonna replace the resitors that feed plate voltage to V1 and see if that helps.

    Enzo has been in my brain telling me to "test parts of the circuit" so been checking resistance from cathodes to ground, and in various other parts of the circuit making sure the resistance adds up to what it should across parts of the network. So far all is normal. Everything that should be grounded is grounded... I also hear Enzo saying "look for horses nor zebras", so I'm looking for my simple error somewhere but just can't seem to find it.

    Does any of the following data help you to help me get closer to the problem?

    Also, I have a signal generator but before I go trying to use it, thought I would ask if there are places in the circuit where I should absolutely not drop a signal in? I've only ever put signal into the input jack of an amp circuit, never droppped one in the middle somewhere. I'm imagining I should be able to drop one on to the power amp first, then work my backwards until I get find where the disconnect is?? Any help is appreciated.


    V1
    p1 103.6
    p2 .00
    p3 .57
    p6 49.24
    p7 1.5
    p8 1.33

    V2
    p1 463.6
    p2 .08
    p3 7.98
    p6 463.6
    p7 .08
    p8 7.95

    V3
    p1 141.9
    p2 .80
    p3 2.17
    p6 105.1
    p7 -.19
    p8 .80

    V4
    p1 159.8
    p2 .12
    p3 1.7
    p6 272.8
    p7 274.6
    p8 272.8

    POWER TUBES
    p3 476.8 & 477.1
    p4 476.1 & 475.9
    p5 -63.9 & -63.9
    p8 0 & 0


    schematic: http://www.jimkelleyamplifiers.com/12.jpg
    ~Semi-No0b Hobbyist~

  • #2
    Yes, V1 seems to be the problem area. First, there is a typo, pin1 resistor should be 150K, not 150.
    Do you have roughly 245V at that supply node feeding V1 plate resistors?
    Do you have those diodes to pin7 reversed by any chance? There should not be DC on pin7.
    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

    Comment


    • #3
      I assumed, hopefully correctly, that the bias caps should be oriented wit their positive end on ground... is that correct?
      ~Semi-No0b Hobbyist~

      Comment


      • #4
        Originally posted by g1 View Post
        Yes, V1 seems to be the problem area. First, there is a typo, pin1 resistor should be 150K, not 150.
        Do you have roughly 245V at that supply node feeding V1 plate resistors?
        Do you have those diodes to pin7 reversed by any chance? There should not be DC on pin7.
        Yeah I had noticed that and used a 150k.

        nodes have:
        A- 474
        B- 461
        C- 294
        D- 172

        they are correct. whit stripes facing toward pin 7
        ~Semi-No0b Hobbyist~

        Comment


        • #5
          Yes, that is correct for bias caps.

          Justin
          "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
          "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
          "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

          Comment


          • #6
            Can you check those C & D node readings with V1 removed?
            And double check V1 pin7
            "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

            Comment


            • #7
              Oops. Did someone forget to draw in the coupling cap off V1 pin 1 ?
              "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

              Comment


              • #8
                Originally posted by g1 View Post
                Can you check those C & D node readings with V1 removed?
                And double check V1 pin7
                with V1 removed
                C- 309
                D- 222

                P7 has about 1.3vdc with V1 installed and about 8vdc with teh tube removed
                ~Semi-No0b Hobbyist~

                Comment


                • #9
                  Originally posted by g1 View Post
                  Oops. Did someone forget to draw in the coupling cap off V1 pin 1 ?
                  should there be a series cap between pin 1 and the pot?
                  ~Semi-No0b Hobbyist~

                  Comment


                  • #10
                    Yes, like in V1 stage here:
                    http://www.prowessamplifiers.com/sch...kelly_facs.pdf
                    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                    Comment


                    • #11
                      Originally posted by mort View Post
                      should there be a series cap between pin 1 and the pot?
                      Yes. The published schematic has always had that mistake. Use a 0.01uF.
                      Good eye g1.

                      Comment


                      • #12
                        ok I tacked in a .01 cap and the DC is off of pin 7 and my plate voltages on V1 are now 101 and 106. Still no output though
                        ~Semi-No0b Hobbyist~

                        Comment


                        • #13
                          V4b voltages are wrong and once again the reason is the schematic is wrong - that 56K(?) should not be going the supply.

                          On the prowessamp link it shows 5.6M to supply and 1.5M to OV
                          Last edited by nickb; 04-24-2016, 08:45 PM.
                          Experience is something you get, just after you really needed it.

                          Comment


                          • #14
                            Originally posted by nickb View Post
                            V4b voltages are wrong and once again the reason is the schematic is wrong - that 56K(?) should not be going the supply.

                            On the prowessamp link it shows 5.6M to supply and 1.5M to OV
                            another good catch. I had read that as 5.6K and that's what's installed. I have a 4.7M I can sub in. do I also need that 1.5M to ground for the circuit to work?
                            ~Semi-No0b Hobbyist~

                            Comment


                            • #15
                              Originally posted by mort View Post
                              another good catch. I had read that as 5.6K and that's what's installed. I have a 4.7M I can sub in. do I also need that 1.5M to ground for the circuit to work?
                              You'll need the 1.5Meg to OV. The aim to to get about 1/4 to 1/3 of the supply voltage at the grid.
                              Experience is something you get, just after you really needed it.

                              Comment

                              antalya escort
                              kartal escort
                              sex vidio
                              altyaz?l? porno
                              antalya escort
                              beylikduzu eskort bayan eskort bayan escort antalya sirinevler bayan escort
                              gaziantep escort
                              Working...
                              X