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My 5e3 Tweed Deluxe is quite poorly, can you help ?

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  • My 5e3 Tweed Deluxe is quite poorly, can you help ?

    My 5e3 circuit amp is made up from a heavily damaged late 1950s tweed Deluxe. Much was lost but the transformers, along with some caps and resistors made it through. All that was missing was replaced and the amp converted to a head along the way.
    Before I bought it the owner even had it fitted with a full compliment of 1950s RCA valves before shipping it to me here in the UK.

    Tonality from the outset was just exceptional, everything you could hope for from this circuit, exept that the amp was somewhat quieter than I had anticipated. I reasoned that perhaps my use of a step down transformer keeping the voltage at 110v may be the reason, given that back in the US it would have seen 115v or more..

    However shortly after after my concern about the lack of volume was confirmed with a comparison with a Fender reissue, I suddenly lost 99% of all available volume. With volume maxed I have the quietest Tweed Deluxe on earth. All is well with the valves, no buzz, fizz, motorboating, redplating or anything else that would cause concern. No excessive heat of transformers or circuit can be detected.

    So.. I have a functional amplifier, with a barely discernable volume.. If youve read this far, thankyou, if you also have an idea as to whats going on here Im all ears

  • #2
    It’s beyond my knowledge but, as a 5e3 fan, I hope you get some help.


    • #3


      • #4
        a tweed deluxe isnt a overly loud amp to begin with but even before things took a turn for the worse, it seems like something may have been wrong. have you opened the amp and looked around for any obvious component failures?


        • #5
          First and foremost, you need to weed out if it is the tubes. Starting with the preamp, replace one tube at a time with a known good tube. If the problem persists, move on to the power tubes. Replace the pair with a known good set. If the problem still persists, then it is in the circuit. With something like that, where it seemed to get worse over time, it could be a number of things. The power transformer could just be weak, the heater filaments could be starved of voltage ( not good ), or you could just simply have a component like a grid leak that has drifted in value dragging the volume down.

          Unfortunately, if changing tubes doesn't do the trick, you will have to open the amp and start taking voltage measurements. I usually start with the heaters and then get HT nodes and plate voltages. I'm looking for no less than 6v and no more than 7v on the heaters. As for the HT nodes and plates, I will refer to a respected schematic with voltage specs on it. The voltages at the HT nodes and plates can vary from the schematic a little bit ( I would say that 20 volts + or - is in the realm of acceptable, and anything 40 volts + or - is highly suspect ). More what you are looking for is if there is one section ( of the amp ) that is starkly different than the rest based on the readings and expected voltages. If V1 is 40 volts lower than the schematic and everything else is about right, for example, then the problem could be based around V1 and its lower than expected voltage.

          If all those major voltage points are correct ( or close enough ) then you need to move towards cathode and grid voltages. The grid of a typical preamp tube should have no DC voltage on it. If there is even a few millivolts of DC on the grid, it will throw the bias of the tube off and can cause all kinds of issues. You more or less rummage around with a voltmeter looking for things that are suspect. Of course, if you are not comfortable with that, then you need to send the amp to a tech. I would suggest that you change out the power transformer for one that is made to work with voltages in your country. The step-down transformer may be doing too much stepping down? Can't tell until some voltage readings are taken.


          • #6
            My thanks to Jeremy and Ewizard for your responses.

            Im looking forward to going through all the valves (tubes) in my amp in the hope that one of them has a fault. Im fortunate to have all of the spare valves needed to complete such a check of the 12ay7, 12ax7, 2x 6v6gt. Im sure I have a spare rectifier somewhere, I just need to find it.

            Speaking of the 5y3 rectifier, could a fault here account for the loss of volume Ive described.? Just a thought..

            Ewizard, Im very greatful for you providing me such a detailed response to my dilemma, and while some technical details are a little above my head I grasped enough to help me take some provisional readings.

            If I get stuck I wont burden you and the forum with details of an amp you cant see for yourself its not really fair, but will pass your post to whoever gets to work on the amp and report back when the amp is finally repaired with all the details.
            Last edited by AcVox; 10-20-2021, 11:14 AM.


            • #7
              yes. the 5y3 could absolutely be the issue or part of the issue.


              • #8
                Different rectifiers have different output voltages. So it can be a factor of your problem is voltage based. I would not suspect a rectifier to be an issue with very low volume. An interesting factoid is that tubes that are 100% fine and in working order can have weird anomalies that cause a circuit to crash. Intermodulation, feedback, and even induction can be a symptom of a tube in a circuit. Change the tube and all those problems can go away. Two tubes, both totally fine, but in that scenario, one just doesn't like what is going on around it. This is usually indicative of preamp tubes, not so much rectifier tubes, although it is not impossible or improbable.

                Just go through the basic steps first. It is usually the simplest thing.


                • #9
                  It seems clear that I should start with the 12ay7 and 12ax7. I have a good selection of suitable nos and current valves to try out.
                  As I thank you for reading these posts, wish me well on my journey..