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70s Ampeg V4B Blows Fuses

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  • Originally posted by g1 View Post

    Did you find out why R28 is burning? (see second part of post #214). Did you get all the power tube heaters running yet?
    There are several problems with your amp and they need to be dealt with, if you have done so, let us know. If not, tackle them before moving on to other issues.
    V4 pin#3 and #8(0.8mv) without V201 installed, 0.4mv with V201 installed.

    Comment


    • Originally posted by g1 View Post

      Did you find out why R28 is burning? (see second part of post #214). Did you get all the power tube heaters running yet?
      There are several problems with your amp and they need to be dealt with, if you have done so, let us know. If not, tackle them before moving on to other issues.
      Anything look wrong about any of these readings in relation to power tube heaters?

      Comment


      • Originally posted by The Dude View Post
        Oh, come on g1, we're only at 224 posts on this one amp. There's plenty of space on the server.
        How much of that do you figure is due to misguided attempts to 'blueprint' the amp rather than just get the darn thing working (and I'm not talking about the OP) ?
        "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


        • Originally posted by ca7922303 View Post

          V4 pin#3 and #8(0.8mv) without V201 installed, 0.4mv with V201 installed.
          And does R28 still measure 1.5K ? V4 heaters are lit?
          With those voltages V4 is not working, so you would not hear anything if you connected signal to 'ext.amp' jack. Is that the case?
          "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


          • Originally posted by g1 View Post

            And does R28 still measure 1.5K ? V4 heaters are lit?
            With those voltages V4 is not working, so you would not hear anything if you connected signal to 'ext.amp' jack. Is that the case?
            R28 is still 1.5k and getting signal thru ext. Amp jack, but not preamp out.

            Comment


            • Have you considered filling in your profile? Maybe there is someone nearby who can take a quick look at your amp.

              Comment


              • Originally posted by ca7922303 View Post

                V4 pin#3 and #8(0.8mv)
                Originally posted by ca7922303 View Post

                R28 is still 1.5k and getting signal thru ext. Amp jack, but not preamp
                Those 2 things can't both be true at the same time.
                If you can get sound by going in the 'ext.amp' jack, then V4 is working. If V4 is working, those voltages would be what is shown on schematic.
                Your measurements are not reliable or they are taken under the wrong conditions.

                Measure DC volts at V4, pins 1,3,6, and 8. (with 120VAC from wall (or variac) and amp on in 'play' mode).
                Keep trying til you get consistent readings that match what it shows on schematic for V4. Dig your probes in and you may even need to sharpen them so they make better contact.
                Until you can get consistent reliable readings you will not be able to do any more with this amp.

                "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


                • vintagekiki
                  vintagekiki commented
                  Editing a comment
                  Your measurements are not reliable ...

              • Originally posted by g1 View Post
                Until you can get consistent reliable readings ...
                Show must go on. Click image for larger version

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                Who does not know and knows that he does not know - teach him Confucius)
                Who knows and does not know that he knows - wake him Confucius)

                Comment


                • Originally posted by Pixel View Post
                  Have you considered filling in your profile? Maybe there is someone nearby who can take a quick look at your amp.
                  Good idea. I hope it's not me (put cringe smiley thing here.)
                  Enjoy. Every. Sandwich.

                  Comment


                  • Originally posted by g1 View Post

                    Those 2 things can't both be true at the same time.
                    If you can get sound by going in the 'ext.amp' jack, then V4 is working. If V4 is working, those voltages would be what is shown on schematic.
                    Your measurements are not reliable or they are taken under the wrong conditions.

                    Measure DC volts at V4, pins 1,3,6, and 8. (with 120VAC from wall (or variac) and amp on in 'play' mode).
                    Keep trying til you get consistent readings that match what it shows on schematic for V4. Dig your probes in and you may even need to sharpen them so they make better contact.
                    Until you can get consistent reliable readings you will not be able to do any more with this amp.
                    V4 pin#1(542v), #3(10.4v), #6(541v), #8(10.4v). Tested with V6 & V8 installed. Able to hear signal thru ext. Amp jack. When V5 &V7 installed pin#3 &#8 go to 0mv and no signal thru ext amp jack.

                    Comment


                    • Originally posted by vintagekiki View Post
                      Show must go on. Click image for larger version

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Views:	60
Size:	27.0 KB
ID:	930925
                      You are not being helpful. Many of your posts in this thread have just made it worse. Maybe reconsider your contributions.
                      What would be very helpful would be for you to learn the official language of the forum and abandon the 'translation machine'.
                      You do not need to know the language if the only things you post are links or attachments. If you want to participate in discussions, being able to understand the language is essential.
                      "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


                      • Originally posted by ca7922303 View Post

                        V4 pin#1(542v), #3(10.4v), #6(541v), #8(10.4v). Tested with V6 & V8 installed. Able to hear signal thru ext. Amp jack. When V5 &V7 installed pin#3 &#8 go to 0mv and no signal thru ext amp jack.
                        What’s the voltage reading at R28 when v6 & v8 are installed. Also check voltage at r28 when v5 & v7 are installed. I am curious to see if there is a difference at r28 between those two conditions. We know that r28 burnt up earlier.
                        When the going gets weird... The weird turn pro!

                        Comment


                        • Originally posted by g1 View Post
                          You are not being helpful. Many of your posts in this thread have just made it worse. Maybe reconsider your contributions.
                          What would be very helpful would be for you to learn the official language of the forum and abandon the 'translation machine'.
                          You do not need to know the language if the only things you post are links or attachments. If you want to participate in discussions, being able to understand the language is essential.
                          Dear friend you're right.
                          I did all to understand you ...
                          Not a problem in understanding the language, the 'translation machine' is quite sufficient to understand what it is about, the problem is in the diversity of language syntaxes, which the other side want or not want understand.
                          Possibility for individual learn the official language it is incomparably greater than the possibilities that 80% of forum participants learn the basics of electronics.
                          But if you say ...
                          Who does not know and knows that he does not know - teach him Confucius)
                          Who knows and does not know that he knows - wake him Confucius)

                          Comment


                          • Originally posted by DrGonz78 View Post

                            What’s the voltage reading at R28 when v6 & v8 are installed. Also check voltage at r28 when v5 & v7 are installed. I am curious to see if there is a difference at r28 between those two conditions. We know that r28 burnt up earlier.
                            I can get readings this evening when I get off work. I've got a 10k resustor @ R28. Any reason to believe thats an issue?

                            Comment


                            • Originally posted by DrGonz78 View Post

                              What’s the voltage reading at R28 when v6 & v8 are installed. Also check voltage at r28 when v5 & v7 are installed. I am curious to see if there is a difference at r28 between those two conditions. We know that r28 burnt up earlier.
                              R28 with V6/V8 installed(10.6v/0mv), R28 with V5/V7 installed(10 6v/0mv).For some reason now all four power tubes pin #1(245v),pin#3(10.5v), pin#6(246v), pin#8(10.5v), and able to hear signal thru ext. Amp jack. Something is intermittent here it seems to me. Still no signal thru input front of amp.

                              Comment

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