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Ampeg SVT 7 PRO U2 (ICE2A165) repair

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  • Ampeg SVT 7 PRO U2 (ICE2A165) repair

    Hi all!
    I have a SVT-7 PRO over my workbench who simply don't work if I connect the Preamp Board (or another 12v charge).
    First to all, the amp came from another tech with a really bad mess with the U2 & asociated components of this PSU (practically all the PCB behind U2 was carbonized). I repair the mess with the carbonized section, replace the ICE for the big one (ICE2A265) and replace too all the PSU components next to U2; then I plug the AC cord (with a protection light bulb to prevent shorts) and the amp simply don't work at first.
    I disconect the Preamp section and again plug and switch to On and the Main Board works fine, with all the voltajes perfectly regulated, so I connect just the filaments of the 12AX7 to 15v and ground and again the PSU don't work, simply can't handle any other charge connected to +15v -15V. I probe the preamp & output boards on a working SVT7 PRO from a friend an the boards are all fine (and put the preamp and output SVT7 boards of my friends amp and don't work) so I know that they're working properly.
    Any suggestions to check the PSU section?
    Thanks in advanced...

  • #2
    Originally posted by Khefer Kaos View Post
    Hi all!
    I have a SVT-7 PRO over my workbench who simply don't work if I connect the Preamp Board (or another 12v charge).
    First to all, the amp came from another tech with a really bad mess with the U2 & asociated components of this PSU (practically all the PCB behind U2 was carbonized). I repair the mess with the carbonized section, replace the ICE for the big one (ICE2A265) and replace too all the PSU components next to U2; then I plug the AC cord (with a protection light bulb to prevent shorts) and the amp simply don't work at first.
    I disconect the Preamp section and again plug and switch to On and the Main Board works fine, with all the voltajes perfectly regulated, so I connect just the filaments of the 12AX7 to 15v and ground and again the PSU don't work, simply can't handle any other charge connected to +15v -15V. I probe the preamp & output boards on a working SVT7 PRO from a friend an the boards are all fine (and put the preamp and output SVT7 boards of my friends amp and don't work) so I know that they're working properly.
    Any suggestions to check the PSU section?
    Thanks in advanced...
    Do you have a spare 12ax7? So what happens if the 12ax7 is removed? Will it still power up? What are your voltages on the tube socket?
    nosaj
    soldering stuff that's broken, breaking stuff that works, Yeah!

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    • #3
      Originally posted by nosaj View Post
      Do you have a spare 12ax7? So what happens if the 12ax7 is removed? Will it still power up? What are your voltages on the tube socket?
      nosaj
      Yeah, I probe anoher one, nothing changes. The amp came with a JJ 12ax7 who works fine too. The Main Supply doesnt work with or without 12ax7, just works if I disconect completely the preamp Board. Without preamp, all the Main voltajes go perfectly fine (+ -15 V, +300v, + -55v and -43v measures perfec). I conect the 12ax7 filaments directly to +15 and GND without conect the preamp board and the power supply doesnt start running.
      It's something weird haha...

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      • #4
        Originally posted by Khefer Kaos View Post
        Yeah, I probe anoher one, nothing changes. The amp came with a JJ 12ax7 who works fine too. The Main Supply doesnt work with or without 12ax7, just works if I disconect completely the preamp Board. Without preamp, all the Main voltajes go perfectly fine (+ -15 V, +300v, + -55v and -43v measures perfec). I conect the 12ax7 filaments directly to +15 and GND without conect the preamp board and the power supply doesnt start running.
        It's something weird haha...
        If I' understanding you correctly and I'm not sure I am.
        Your preamp board possibly still has a short on it.

        Also from what I understand SMPS power supplies do not generally like a dim bulb tester. You also need to be very careful with the smps supplies.

        Can you post any pics of the repair section?

        Thanks,
        Jason

        nosaj
        Last edited by nosaj; 08-04-2018, 01:53 AM.
        soldering stuff that's broken, breaking stuff that works, Yeah!

        Comment


        • #5
          Originally posted by nosaj View Post
          If I' understanding you correctly and I'm not sure I am.
          Your preamp board possibly still has a short on it.

          Also from what I understand SMPS power supplies do not generally like a dim bulb tester. You also need to be very careful with the smps supplies.

          Can you post any pics of the repair section?

          Thanks,
          Jason

          nosaj
          Ok, tomorrow I post some pics. The preamp is working right, I put it on another SVT7 and all are perfect, not shorts or malfunctions, just works like a new one...

          Comment


          • #6
            Sorry, I can't post photos, i don't know why. Whatever I follow doing some tests:
            I work the PSU without bulb dim, but with no differences, so again, disconection of +-15V (and even 300v to 12ax7) was the only way to work with.
            Putting an external power supply to the preamp was one solution (300v, +-15v), so whit this, the amp works great (ICE chip runs normaly and cold). So I'm thinking in let the PSU +-15 only supplying the power amp section and do another supply for the preamp.
            Any suggestions???

            Comment


            • #7
              My 7 Pro has had problems with U2, and I switched from a real tube to a Retrovalve FET replacement to get rid of the tube heater load. I actually like the sound better.

              Comment


              • #8
                Retrovalve FET its a "Solid State Valve"? One of the options on my mind, was to rid off the Valve and doing this stage with two fets and a bias of 4.5v like a valve emulator...

                Comment


                • #9
                  Originally posted by Khefer Kaos View Post
                  Retrovalve FET its a "Solid State Valve"?
                  Yes. http://www.robertsaudiotech.com/designs/retrovalve.php

                  I find them really useful debug tools as well, rather than having some "golden 12AX7" or something. I have to say the LED bulb inside is a little bright if they were trying to emulate the soft glow of a tube heater.

                  Comment


                  • #10
                    Revision H01 SVT7

                    H01
                    New Power Management IC (U2)
                    Current IC overheats. New IC ICE2A265 runs cooler.
                    Replace U2 0026347 with 2046141.

                    Comment


                    • #11
                      I'm in Michigan looking at the exact same issue. Ampeg SVT7 with blown U2, open R46 and bad D9. Can I chime in with questions along this line or would you rather I start anew? Thanks, Mike

                      Comment


                      • #12
                        To all that have been reporting this members posts... I believe there is a lack of adware blocking on their media and I don't perceive this as intentional spamming. Member checks out otherwise as far as I can tell.
                        "Take two placebos, works twice as well." Enzo

                        "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                        "If you're not interested in opinions and the experience of others, why even start a thread?
                        You can't just expect consent." Helmholtz

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                        • #13
                          If this is in regards to the Retrovalve link, I found that an interesting device, never having seen them before. It does figure someone would have built such devices for commercial sale by now....I've just never come upon them before.
                          Logic is an organized way of going wrong with confidence

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                          • #14
                            This patent is from 1973.

                            US3742261 SS Device _Vacuum Tube Replacement.pdf

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                            • #15
                              Hey guys… it seems as the U2 IC upgrade chip ICE2A265

                              ​ is now obsolete.

                              any suggestions on a replacement?

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