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Peavey Classic vtx series- Troubleshooting repair help needed!!!

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  • Peavey Classic vtx series- Troubleshooting repair help needed!!!

    Hello to all,
    Recently I had picked up a Peavey classic vtx series combo out of a storage unit, it was sitting in the corner rotting away with the ages and had caught my eyes as most musically driven items do. What also helped was the re-cover job-(burlap and staples) - with grim results, that led me to want to save this amp. So, I dug her out- FS and all and took her on home.

    Upon a thorough external exam, everything seemed to be intact- Power tubes, Reverb pan, the FS was in fair to poor condition, had all its knobs and the pots where a little stiff. External fuse was good and intact. Power cord was missing its ground prong and slightly frayed. Speaker jack was in good shape and the speakers seemed to look ok, except some age. We all know about looks- there deceiving. So, I proceed w/ plugging it in and powering it up accordingly- everything is in check- status led’s are working , no cracks or pops, funny smells, tubes are operating good from visual inspection- glowing evenly and not operating overly hot. So, I plug in the guitar and turn the standby switch. Wow, what a bummer- very weak low volume w/ a hissing/buzz. Everything is still in working properly just there is no great sound coming from this thing as I have read these things are pretty perky when working correctly. Frustration gets the better of me for a bit, and it is retired to the GARAGE!!!!
    Few days later I decide to pull it out of the COLD garage, let it warm up for a few hours, throw some newer 6L6’s in her I had lying around, power up accordingly, and “damN” She was off to the races, nice and loud at reasonably low settings, full of tone variations, the FS was even working considering the shape it was in. Everything seemed fine- Then in the middle of our new found love affair, she turns and walks away, back to the comfy confines of her previous state- low volume w/ a hissing buzz!!! Thinking of course, swapping the tubes with some old ones I had laying around was the fix last time, I ran out to buy some new tubes to see if this would be the fix. Nope, same story w/ the new tubes. So, I proceed to plug directly into the back of the chassis to the “power amp in” jack. The power amp works remarkably well, although there is no volume control (normal, there is no preamp control- it’s bypassed). It sounds ok, and I spent a minute playing through it this way. “Power amp is fine”!!! Next, what I do know is that the preamp out and the power amp in jack are wired together in a relay of sorts, so to see if the connection was bad between the jacks internally, I connected them externally w/ a ¼” 90deg. Patch cord. Still the same result- Low volume w/ a hissing/buzz! That leaves me with no other option but to break her down and get it up the bench. I start this as I do any other rebuild or repair- An extensive research campaign, finding any and all info. I can about this particular amp. – Schematics, Calls to Peavey, Forums, Internet, Books, Astrological Signs and Moon Beam Deflection- Kidding!! Upon some learning a little more of this amp., I begin an internal examination of the chassis, pcb’s, wires ,internal fuses, solder contacts- everything seems to be fairly clean and in good shape no funny smells, bulging caps, fried wires . Clean it all up, flushed pots, cleaned pcb w/ board cleaner, cleaned some contacts, and replaced the a/c line cord with an exact gauge match that had a ground prong. Reassembled, same as before powering up and still the same results. Low volume w/ a hissing/ buzz.
    So, I proceed to take some of a fellow owner of the same amps advice with the same symptoms and some suggestions from peavey to try and correct these problems.
    First, I replaced the audio driver transistors located on top of the heat sinks on the pre-amp board.Here are some pics of the new transistors in place.

    Second, I replaced the driver transistors, Here are some pics of the new transistors in place.

    Fairly easy replacements, I have a bit of experience w/ PCB’s and the soldering was perfect on theserepairs,hard to locate they blend in w/ the factory contacts. Gave it a good examination to make sure everything was correct and reassembled, and began the precursory fire up and “BOOM” I’m blowing internal fuses now!
    Here are some pics of the power board and the fuses that are blowing.

    The amp will remain on and the power led will start from nothing and increasingly get brighter to a degree, the standby led doesn’t work at all, all other fuses are ok, and the tubes are seemingly ok-not overly bright, overly hot, no strange arcs or pops other than the two internal fuses.

    I have a few ideas as to what it might be but was interested in some feedback and possible help narrowing it down. Or, quite possibly I could have overlooked something or done something wrong. I am fairly new to the Amp. Tech world itself, but have some experience and am aware of the dangers and how to avoid them. Feel free to school me on the knowledge and the no-no’s, after all any help would be appreciated. Thanks and happy holidays!!!
    Brian

    I also have a bunch of other pics of this amp!!!!!

  • #2
    Peavey Classic VTX

    Did you get a schematic taht you can post from Peavey.
    If the amp is anything like the 5150, the 1 amp fuses are for the + - 25 volts.

    Comment


    • #3
      F2,F3 are the fuses for the +/-15v supplies.

      If they are blowing, look first at the four rectifiers, CR7-10, then check the filter caps C6,C7. Looking for shorted parts.

      The 15v zeners could be shot, but that wouldn;t usually blow fuses.

      But there is a little four pin cable over to the preamp from the power supply board. In your photos it looks like 6 pins, but I think only the center four conductors are in use. Make sure that connector is not off one pin either direction. But you could also just unplug it to see if that affects the fuse blowing.
      Education is what you're left with after you have forgotten what you have learned.

      Comment


      • #4
        Troubles Solved!!!!!

        Well, sorry for the slow response- holidays and all!! Anyway, funny story!! The day after my initial post, I sit down once again to get to the root of the problem on this thing- and "POOF" right in front of me is the ribbon connecting the power supply board to the pre-amp board is a little askew, It was off by 1 pin- In an elated burst of excitment, I run to the computer to report my findings and see that I had a reply on the forum- It was the answer to my problem, right on the money, althought I had already caught my "stupid mistake", I was impressed by the diagnosis and it taught me a good lesson- "pay attention"!!!! Thanks guys for your replys and all your help!!

        The amp by the way sings to no end!! The variations in the tone are fun to play w/!!! Its as quiet as can be too, sitting idle you cant even tell its on.

        [IMG][/IMG]

        Looks alright- but could use a new covering!! all-in-all not to bad for a storage unit find- cant beat free!! Thanks again!!

        Comment


        • #5
          driver update

          i have the same problem with my classic and ordered the drivers, the 2n3904 are still used but the mje15030 are now mje15032, they sre rated for 250vdc instead of 150vdc.

          Comment


          • #6
            Classic vtx

            Hello all. This is my first post here. I am trying to fix this amp for my brother-in-law and I am in need of help. I have the same symptoms listed in this thread,
            Sound- low and distorted
            Power led comes on but not Status (I had the status light come on once, when it did, the sound was full and powerful but faded away after about 30 seconds.)
            Tubes, seem to power up fine ( I don not have a tube tester)
            I tried plugging the guitar straight to amp in but still had the same results, low distorted sound.

            It sounds like the drivers are what needs replaced. Any advice on where to get these parts?
            Smolty: It looks like you had ordered the drivers for your amp. Did you get them replaced? If so, how was it, and are you having any problems? Any help would be greatly appreciated, Brian.

            Comment


            • #7
              Welcome to the place. This thread is so old, I doubt that the OP is still hanging around here. Why not start a new thread for your amp?

              From your description, It sounds more like a mechanical problem like a broken connection, than a driver transistor. If you give the amp a good Enzo whack with your fist, can you get any change in reaction from the amp?

              Start by contacting Peavey and ask for a copy of the schematic for your amp, it will help in relaying information back and forth here on the board.

              Comment


              • #8
                Hello and thanks for the welcome. I figured I was taking a chance posting in such an old thread but it really did seem to fit my problem. I have to admit, I dont play (yet) but I am a huge audio fan (not audiophile) and I like to work with the vintage equipment. I thought as nicely laid out as this preamp is, it would be doable, otherwise this poor amp would just be sitting in my brother-in-laws storage unit.

                I did try light taps with the "universal alignment tool" but no luck.
                I did take it apart and do a search for loose or broken connections and once again, tried very light taps (with the handle of a screwdriver) here and there to try and reveal a loose connection but no go.

                I have powered it up a couple of times now and when I flip the stand by switch, the status light turns on and I have about 30 seconds of great sound and then back to low distorted sound.

                I do have a schematic for the amp now, but I am still trying to get registered with the peavey forum. Thanks for the help! I am still leaning towards the transistors as the problem, but will continue to do more search. Brian

                Comment


                • #9
                  That is different than your original post, I though that you said it only powered up the status light once.

                  I don't have access to the schematic right now, but a good place to start is by checking the voltages in the power stage. Look for the voltage that initially starts out fine, but slowly changes as the sound fades out. Then try and figure out what is causing the voltage to change.

                  Comment


                  • #10
                    You are correct sir. It has done this ( status light on) 3 times now with the same result each time. I am no expert so bear with me.
                    I completely agree with the voltage issue.
                    This is something I did not mention before, but when switching to low power on stand by (after power up) once I pluck a couple of strings the sound quickly goes from low and distorted to nada, zip, zilch. Just like once voltage is applied, something gives in, or is not operating up to spec.

                    52 Bill, thank you so much for the help! I do have a m.m. and understand enough to know when to say when, so I look forward to any more info/help. Thanks again, Brian

                    Comment


                    • #11
                      Hi Marley I'll add my tuppence worth here and add the schematic for (hopefully) others to follow.
                      Firstly It would be good to narrow down the area the fault is in.
                      Although initially it looks like power supply-output stage fault (diminishing HT) maybe check a few things to make sure you're on the right path.
                      Firstly to make sure its either in the pre or power amp stages you can make use of the effects loop the preamp out/poweramp in jacks.
                      Connect a seperate amp input to the preamp out jack of the Classic ..guitar in to front panel jack on classic ...classic preamp out to external amplifier.
                      According to the schematic this should work without the standby switched to operate
                      low or high.
                      Bearing in mind the signal to the second amp will be greatly amplified so watch levels.
                      If thats all good it points to the power amp if not check the 15 volt supply see attached jpg.
                      The zener circuits do dissipate a lot of heat so it may pay to look at the solder joins
                      on the reverse of the power board particularly around the zeners and associated resistor.
                      + 15volts is also fed to the grids of the 6L6's via R112 (100 ohms) so maybe check that
                      as well. i.e. measure between junction of R112,113 & 114 and ground.
                      If not C 50 (22uF 25v) could be faulty.
                      Feeding a signal (ipod/cdplayer with volume control) into the power amp in will check if the power amp is ok in isolation bearing in mind the level from the player should be low as the Classic has no volume control after the power amp in jack.
                      Setting your MM to the high DC volts setting as Bill52 suggested monitor the voltage at
                      the power board when the s/b switch is set to low and high and observe if it fades away.
                      Likewise with the above +15v after R112.
                      Attached Files

                      Comment


                      • #12
                        Thanks for all the advice. Although I cant stop thinking about this amp, it is mothers day weekend and I need to spread the love. Once I can try a few of the suggestions, I will report back. Thanks again, Brian

                        Comment


                        • #13
                          Just thought I would touch bases with yous guys that are helping me out with this. I really feel confident that I can fix this.
                          I have talked to my brother in-law to let him know where we stand, and what I need from him to help me out. You know, I love my brother in-laws' laid back attitude but sometimes its a real pain in the butt!

                          By that, I mean I have not been able to completely rule out the power amp. Not to worry, I know a few other musicians that might be able to help me out.

                          I have to say that from what little I have heard from this amp, I want it. I found out that this amp has been sitting inop. for at least the last 10 yrs! My brother in law couldnt even tell me the procedure he used to power the amp up. (power on, while stand by is in the neutral position, and then flip stand by to high or low?) Again, I am just learning to play, but I could have alot of fun with this amp! Brian

                          Comment


                          • #14
                            I was able to get my neighbor to help out and we discovered that the problem is in the power amp. Using my pre amp into his amp, sounded great!
                            Now I guess the first thing to do is have the tubes tested. Could it be that simple? I doubt it. Brian

                            Comment


                            • #15
                              It just ocurred to me before you get too technical..after reading your post
                              that if the standby switch was faulty (eg had been arcing) that this could cause the fade...
                              Sometimes the obvious escapes... anyway just a small point..
                              Also occasionaly the crimped internal wires with spade connectors can
                              be faulty so examine them. Sometimes I attach a meter with a continuity "beeper"
                              with strong alligator clips onto the spade connectors then wriggle and pull on the wires
                              and observe if the beeping stops.If the wire comes out can often clean the connector top and resolder covering it with a bit of heat shrink.
                              Have you got the user manual ?
                              http://www.peavey.com/media/pdf/manuals/80343008.pdf
                              I presume this one is the same as yours with the 2 inputs.
                              Peavey did make several classics I think the majority have made it to this forum over the years.
                              Although not your VTX here's another that was resurrected ! (4 inputs)
                              http://music-electronics-forum.com/t20714/
                              http://music-electronics-forum.com/t20737/

                              regarding tube testing .. usually a new pair is tried or old ones put in something thats known to work. I would check the voltages first before plugging in a new set.
                              As the pre-amp works you should find the 15v (well a bit less) at pin 5 of the 6L6.

                              Another thought (geeze I've got to stop having these) in case its the last IC U8A
                              a 4558 causing trouble - borrow the one from the reverb (U6) and put it in U8's position. Be careful not to bend the pins and observe which way they go in.
                              Last edited by oc disorder; 05-11-2011, 02:13 AM.

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