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1960's Barvic 15AM tube amp with Lenco phono

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  • #16
    thanks g1, I will follow that lead and see where it takes me...


    • #17
      Sounds like its going well.
      Changing those capacitors gives you hands on experience in component placement.
      A lot of the new ones are smaller so you will be able to make it a bit neater hopefully !
      From another post here found myself led to this site.


      Seems to be a lot of good "Olde Worlde" articles there which make interesting and educational reading.

      The mic transformer may be there so an extra long mic lead can be run.

      If it's a 3 wire circuit - positive going wire ,negative going wire all wrapped in a metal shield, it would be a low impedance balanced circuit.

      This is a clever trick .. any noise induced into the positive and negative wires cancels ... leads to differential input.

      Has a relationship to the twisted pair reduce interference etc.

      As a mic signal is such a small voltage (not exactly a kilovolt generator) the lead can be susceptible to picking up interference.

      Phantom power to microphones too is an interesting concept. Using the same 3 wires , DC about 48volts is fed down the audio line
      to power the microphone with active circuitry and doesn't affect the audio signal.

      This is additional stuff to basic theory but gradually it starts falling into place..

      98 pages here .. one of the first books I actually sent away for many many moons ago .. that helps fill in a few gaps.

      The Electric Guitar Handbook by Jack Darr. (4.3megs)


      • #18
        Mica caps (postage stamp) for schematic

        I have been attempting to read the values of the postage stamp mica's, and I believe I have figured it out, for example, reading left to right, (all mine are JAN (first dot black)), so "black, red, green" top row = JAN, 2, 5.

        The bottom row (left to right) "brown, yellow, brown" = "class", "tolerance" (+ or - 4%), "multiplier" (10).

        so I have 25 X 10 = 250 pF.

        If this is correct logic, please let me know--AND what is concerning me is what about Voltage? all the other caps I am replacing (not replacing mica at this time) have voltage designation...

        I would like to put voltage for mica on schematic, and I may need to replace some micas after start-up, so can anyone explane or give me direction? thanks


        • #19
          James Grey1 day ago
          Hi, am am currently rebuilding a tube PA from 1962 (Barvic Eng.) and it has 8 of the "postage stamp" micas (areovox)...finding this vid was very helpful, and

          my question is re: voltage...

          In replacing all the other caps (electrolytic, etc.), voltage was an important consideration...I have spent three hours over the past 5 days trying to find info on the voltage of the mica caps, with no luck...

          is voltage a non-issue? or is there a way to read it from the dots. Thanks

          Mr Carlson's Lab
          Mr Carlson's Lab1 day ago
          +James Grey
          Hi James. Most modern Mica's are 500 Volt rated, and the majority of the older Domino's were 400 Volt rated. If in doubt, just purchase a Mica capacitor with a voltage rating higher than the B+.


          • #20
            Barvic diagram (schematic)

            Well, after many weeks of strain, agony and enlightenment I have completed a reverse engineering diagram of the tube amp.

            I welcome feedback, and I realized during the process that my lack of knowledge of how-to wire something lead to way to many lines, particularly ground wired (though I may be wrong, but my diagram is so much "busier" than any other schematic I have seen, thus I believe my "novice-ness" is laid bare in this effort).

            Now that I have the diagram, I am going to start replacing the Caps, then boot it up and test for sound quality...

            then convert it to a guitar amp, building a cabinet etc..

            Thanks again for all your help in guiding me to this point...


            PS. not knowing what is best way to post the diagram, I provide three opportunities to view doc...two of them require "magnifying" the image, but the diagram scales well...



            Struggled with attachments, .png file would not load, so hopefully the .pdf and the digikey link will work


            • #21
              That's "Great !" James !
              Zero info to schematic in 2 months ! Must have surprised yourself!
              Now you have your own answer to the question " what is it that I have, exactly? " and when the next
              bloody ignorant junior knocks on the door and asks about a Barvic amp we'll build a wall and make them pay for it
              (just getting carried away with Auzzie humour and your election campaign... getting ready for Trump Speak- excuse me)
              that should read and when the next inquiry comes about a Barvic we can point to your post which is now most informative!

              Oh I didn't realize Digikey had that free schematic drawing program on line. Great !

              Here's a another free bit of test gear I'm about to explore. Took me 2 hours to find the on button (top lh cnr).

              Visual Analyser details

              Visual Analyzer is a free software oscilloscope made by Sillanum Software.
              They describe it as A complete professional real time software that transforms your PC into a complete set of instruments.
              No new hardware is necessary (you can use the Sound Card of your PC).

              There's some zip files with a defunct magazine article in Italian on how to build a hardware interface.. which I'm attempting to translate.

              Once again James great effort !!


              • #22
                Thanks OC, glad you took a look, and you (once again) nailed how I feel about completing and my hope it is of value to others...I hope to look at your links today to see what further mysteries your are "lighting" up...

                yesterday I was "proofing" the schematic by replacing caps and tracing their individual circuits before R&R, and found a 25 25v off of EF86-2 that I missed totally (which, I guess, is better that having mis-wired it altogether---so I am going walk-the-walk-of-shame and post an accurate one ASAP, after proofing the cap circuits, and preying the rest is accurate (I am confident, yet I was confident before)...

                Translating Italiano? just how many autodidactic skill-sets you got, Aussie? Here I thought down-under was a kangaroo filled desert without much electricity or woman and way to much sun,,,this electronic adventure I am on is enlighten more ways that I expected!!

                Thanks again and bye for now


                • #23
                  up-date on Barvic Amp & "Wiring Diagram" & a question

                  I have the Barvic up and running and the sound is pure, clean, clear...running it through the speaker that it came with (6" RCA from 1950's?) and the bass is excellent, and the treble & bass pots work well...I had posted early on that the amp worked and I had played a record, & found the bass & treble did not work...same now, but the "wiring diagram" (I was informed by an electronic engineer that my schematic effort was mostly a "wiring diagram" with some schematic features, which make sense to me) shows the mic is set up for the pots, so I switched to running the signal through the mic and low, the bass was better and attenuate-ible (ditto treble)...

                  problem I have now is my plan to convert it to a guitar amp has been overwhelmed by the sound-space this amp/speaker produce...I now loath to modify it, taking it so far away from it's creators intentions, so I am now thinking of another option...more on this later...

                  I am going to modify the "wiring diagram" (having had some mentor-ing) into a more usable/efficient schematic-like document, will post this soon.

                  I posted a week ago that I had "dropped" a 25 25v cap from the diagram--turns out this is false, I did find it eventually, while "proofing" another circuit, and it was wired correctly...I did find some small (if I may judge from my "junior" perspective) errors, like having a cap wired after a resistor, while being on the same circuit to my inexperienced eye, 3 or 4 of those, and a 100K resistor ID'd as a 1M, but that's about it.

                  I do have a small regret, that the amp did not have some problems that I would gain experience trouble-shooting, but hey, be careful what you wish for and all that.

                  I will finish with a question: I first ran the stereo signal through just standard pair of RCA jacks and sound was wonderful, then decided to try connect both channels through one RCA, and it worked, at least to my ears, but I have now understanding of what kind of signal I am creating for the amp to use...any thoughts/experience?



                  • #24
                    Barvic schematic hybrid

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ID:	841839here is the latest Barvic Schematic incarnation...not sure if I have attached it properly, so this post is a check/test
                    edited in later: okay, seems workable


                    • #25
                      Help with ID of these two transformers & what they do

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                      The Barvic had two transformers, the 119H is in speaker cabinet and brings signal in with jack, signal goes through and then to speaker (Note: in proving amp worked with speaker, I had to bypass transformer) not sure what it does nor where does it get it's power from? (if needed, by the looks of it it does not).

                      The second Trans #46090 is in cabinet with amp & phono: it has 4 wires one side, 5 other: wires running to two jacks and 3 connections going to speaker connectors, two green (4 ohm & gnd), a lime green-jumped-to-white that goes to 16 ohm speaker connector (8 ohm is ID'd on speaker connectors, but no 8 ohm wire).

                      Speaker is 4 ohm.

                      I am mystified and I find no reference as yet on Internet--hope you can help.


                      PS. FIles are +1M and I do not know id there is a smaller way to send pics...sorry and I'll work on it
                      Attached Files


                      • #26
                        Hi James

                        I suspect they are line transformers to enable multiple speakers from the one source without loading it down.

                        They could make good output transformers (one could be an o/p trans. used as a line trans.)

                        The word line (above) has nothing to do with the electricity supply to your power outlet as they are audio transformers.

                        Voltage can be seen as pressure.
                        However electricity distribution is a useful analogy without going into too much detail.
                        Here our power is 230vAC (was 240vAC).

                        If we put an extension cord with 230v across the Nullarbor Plain (Desert) with junction boxes on the way there wouldn't be much left at the other end due to resistance.
                        So what the power company do is run 22,000 volts across the poles and every time there's a farmhouse in need of a power outlet they put in a step down transformer from 22,000 to 230 v.

                        Similar to speakers. Step up the output and run 1 pair around the showground or whatever.
                        Every time you need a speaker in a position connect it via a transformer.

                        The impedance is high. You can get away with a lot of speakers which you can't do on a 4Ω o/p with 2 wires.

                        Hammond Mfg. - Sound Distribution and Speaker Matching Transformers - (117 - 119 Series)

                        Audio Transformers (scroll down)

                        Last edited by oc disorder; 05-09-2016, 09:34 PM.


                        • #27
                          Hi again James

                          All the info is on the diagram you did but it is a little hard to navigate.

                          I usually start off with ones by hand which become messy then gradually refine them.
                          Using the online circuit drawing program would be a huge challenge in itself particuarly
                          when you are still becoming familiar with the symbols.

                          But "cutting to the chase" a bit of refinement is in order so we can see at a glance the signal path.

                          I'm using an art package which is a clumsy way to do it. The last drawing program I had was for an Atari !
                          It actually worked and I could print a pcb and have a negative made !

                          Unfortunatelythe smell and chemicals didn't go down well at home !

                          I couldn't figure out R8 coming from the cathode (HT) of the rectifier and going to the 16Ω tap
                          on the output transformer then I realised the negative feedback resistor R3 was going to ground
                          and that it's just the J2 connector reversed.

                          R8 must go to ground at the rectifier and I suspect it shares it's ground with the output transformer.
                          I realise you like to show where the various ground points go or are common and actually this is a good
                          Often by moving a ground wire to another point in the amplifier can reduce noise.
                          Bit like ground loops (hum) but within the chassis one part of metal to another can contain (eddie eddey ?)
                          eddy currents .. getting out of my depth... but a lot of new amps now use the star grounding method.

                          Human version

                          Complicated Version
                          Staying Well Grounded

                          Keeping track of your grounds to me is a good idea but on the diagram it would have been far easier
                          just to drop the resistor from the cathode to a ground symbol.

                          You could however put an asterisk *g1 *g2 *g3 etc on them so you can tell where they were physically connected.
                          Also notes as you have done, help.
                          The grounded shields for the EF86's could be left off the diagram and mentioned in the notes
                          eg NOTE:Both EF86's have internal shields on pins 2 and 7.
                          Although not shown on the diagram these are grounded at the respective tube base.

                          Here's what I did one rainy afternoon...

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                          PS re my translation attempts well actually using google but have to first organise an image for the free
                          ocr program to scan... then paste that on to a text document and organise in managable paragraphs.
                          Paste the text into Google Translate then paste the translated text into a new document.
                          Still quicker than learning Italian !


                          • #28
                            Hard to navigate is a huge understatement...

                            Thanks for all the info and links...

                            I found I had to just let go of the schematic after my last post, 21 days in a row and I was burned...I downloaded LTSpice (student version) and am playing with that, and will use it with the 4 diagrams you sent me, and then build up a real schematic...have gotten away from electronics per s'e (is that a word?), but picked up a Westinghouse 697 A since posting, and am doing the wood work on the cabinet, just to rest my brain...will be back to schematic and re-capping within about 2 weeks, so will follow up then on project(s)...hope all is well at your end at the bottom of the world.



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