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Newcomb Pathfinder E-10B

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  • Newcomb Pathfinder E-10B

    Hello all

    I would like to seporate the 2 imputs on this amp. I bypassed the input transformer already and installed 1/4 input jacks on the phone spot . The amp sounds cool but their are no bass , mid pots and the treble seems kind of odd. If you turn it down you get more treble. Are their any mods i can do to inprove on the design. can i seporate the 2 channels and how would o do that?

    any ideas welcome

    thanks alot
    Attached Files

  • #2
    Newcomb Pathfinder

    I would like to get a little more volume Not Distortion) from this amp. IS there a way i can achieve that by modifing this design. What would happen if i increast the plate voltage in the preamp section ?

    Last edited by tboy; 11-07-2008, 08:12 AM.


    • #3
      I seporated the 12ax7 channels at the .5 meg mike pot and lost all sound from that input. The other input works fine. Do i need to instal another 12ax7 preamp in front of the existing one to drive that 1/2 of the tube? It looks like 1/2 of the 12ax7 is being used as the phaze inverter. Am i correct?

      anyone out there


      • #4
        I figured it out thanks to everyone for responding. NOT


        • #5
          I'm glad you got it figured out------- a big part of converting these old PA heads is experimenting, trying different things, and seeing what works to your ear.
          i recently joined this forum but i'd think that most people on here haven't seen the Newcomb E-10B circuit and really didn't know how to respond to your questions.
          I have a Newcomb E-10B head (and matching orig 1x8 speaker cab--- now it's a 1x10).
          I got tired of modding the orig oddball Newcomb circuit with the 6au6 so i built a version of the Fender Tweed Deluxe 5e3 circuit into mine and it sounds killer---- new filter caps, all new circuitry, pots, etc.
          I'll often run this head into a 4x12 cab to show people just how much sound a 10 watt amp can produce.
          I recently built a BF Fender non-reverb Princeton head (no trem) with a vintage Schumacher 4/8/16 ohm OT. Another sweet sounding small head.
          Sometimes friends will come over and we'll run these small heads thru 4x12's and jam out and not have the typical ear-ringing that the big amps produce.
          Lighten up and have some fun learning about tone/tweaking by working on these Conversion amps----- having somebody spoon-feed you the answers isn't as much fun as finding them yourself, IMO...............gldtp99
          Amp Clips:


          • #6
            I stuck a fender champ tone curcuit between the 12ax7 and the 6au6 and it sound ok but i was wondering if i could swap 6au6 with a 12ax7. Im not sure how to do that and am always concerned about burning up transformers and other parts. I dont have very much money and cant afford to take electronic classes. Sorry for being short i thought that a curcuit is just a cuircuit. I didnt realize their is such a differance in curcuits. I do apreciate the help i do get here .



            • #7
              Yes, all tube audio circuits are somewhat alike but a lot of us on these forums don't have a deep backround in formal electronics training, if we get too far away from the familiar then things get confusing---- there are many that do have a deep understanding of tube circuits but often they are quite busy and don't always respond to help with old PA conversion projects.
              The info for the US Navy electronics course is available for free here:

              A 12ax7 gain stage/Phase Inverter can be installed in place of the 6au6---just follow the Fender 5e3 schematic.
              The way Newcomb uses the 1/2 12ax7 and the 6au6 for the PI on this amp never made good sense to me so i just converted to the 5e3 circuit, with a single input-----it's one the the favorite circuits for amp builders and it sounds terrific.
              On the Hoffman forum there are some very knowledgable folks who like to help out with oddball projects--- they have quite a library of project schematics and maybe somebody's already done this circuit----if this circuit isn't covered there already, try posting there anyway----maybe someone can help................gldtp99
              Amp Clips:


              • #8
                When you did the conversion did you you changed the rectifier tube to a 5Y3GT. Did you use the existing power and output tranys? Schematics heavins 5E3 schematics doesnt show grid voltages . Can you past a shotcut to the Hoffman Forum it sounds like a cool place for info. Did you see my other posting for the Rauland amp .



                • #9
                  I used the orig PT and OT, nothing wrong with the Newcomb units-----i also used the orig 6x4 rec tube----- this PT doesn't have a 5VAC filament to power a 5y3 rec tube so why not use what's already there, it works just fine for a 10 watt amp.
                  Here's a link to the Hoffman forum:
                  Hoffman has a large collection of schematics---- maybe the voltages are listed there.
                  Yes, i saw the old Rauland amp---6L6x6 ? ---I've come around to using 12ax7's mostly in preamps (sometimes a 12at7 in a PI for some amps)----- they are plentiful, great sounding, and last a long time in most cases----i went through a period where i tried different types of preamp tubes but now i'll stick to 12a-7's---- also if i sell an amp to somebody and a 12ax7 dies, another 12ax7 can be pretty easily found---if i used 6eu7 (looks just like 12ax7 externally but has different pinout and runs on 6 VAC heater) and they stuck a 12ax7 in it's place then there could be big problems besides the amp not working.................gldtp99
                  Last edited by gldtp99; 11-11-2008, 09:59 AM.
                  Amp Clips:


                  • #10
                    Thanks for the help on the newcomb. I worked on the Rauland ( it only has 2 6L6 tubes i had a misprint) while i am wating for parts . I changed out the 50 v e-caps , wax paper caps and cleaned the pots. The thing fire up and it sound cool ( overdrive baby) and its a very quiet amp. These things where built to last.

                    Last edited by baddog; 11-11-2008, 12:52 PM.


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