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  • 5e3 build questions

    Getting ready to build a 5e3 as my second build. My first was a champ and turned out great. Is there anything that I need to specificaly pay attention to that will be different from a champ or any tips will be greatly appreciated. Also what is the best grounding scheme. On the 5f1 I put all the preamp grounds on one side and all the power and high voltage grounds on the other side and its really quite. I have seen the back of the pots used as a ground rail also. But you still want to separate the pre and poweramp grounds dont you? Thanks.

  • #2
    Originally posted by rockinmac View Post
    Getting ready to build a 5e3 as my second build. My first was a champ and turned out great. Is there anything that I need to specificaly pay attention to that will be different from a champ or any tips will be greatly appreciated. Also what is the best grounding scheme. On the 5f1 I put all the preamp grounds on one side and all the power and high voltage grounds on the other side and its really quite. I have seen the back of the pots used as a ground rail also. But you still want to separate the pre and poweramp grounds dont you? Thanks.
    If you don't have a brass plate behind the pots and jacks.... use raw zinc plated lock washers under all of them.
    Pull the grounding lug of the two volume pots right down and solder them to the pot's shell.
    The first two filter caps (or all three) negative leads can be connected.
    Main thing is to bring the red/yellow center tap from your high voltage secondary right to the eyelet of the negative lead on the first filter cap... you can then run a ground wire from there to the chassis.. like a PT mounting bolt with a star washer lug.
    The preamp stages should be ground well away from that point... ground the 12AY7's 820 ohm resistor and it's bypass cap, of the 1st preamp tube to any of the grounded lugs of the input jacks.
    Ground the 12AX7, second preamp stage's 1500 ohm resistor and it's bypass cap with the grounded 56K resistor, close to the tone pot ground or at the negative lead of the third filter cap.... and don't forget to ground the 220K power tube grid load resistors to the negative lead of the third and final filter cap's negative lead too.
    If you have a 6.3vac filament transformer with a center tap... bring that wire...(usually green with yellow stripe) ...
    over to the positive end of the power tube's cathode biasing resistor or right at the first 6V6 tube socket lug 8.

    If you don't have a center tap, use two 100ohm to 150ohm 1/2w resistors across the two 6.3vac leads, to make a virtual center tap, and connect the junction of those two resistors at the cathodes of the power tubes.
    Should be pretty quiet.
    Bruce

    Mission Amps
    Denver, CO. 80022
    www.missionamps.com
    303-955-2412

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    • #3
      Thanks Bruce!!! This kit is a mojotone and Thanks for the Very helpful info. Is it alright to run a wire to all three pots or is that a bad idea. I plan on building another 5e3 what are your PT secondary rated at i know mojo's is a little hot. the next build i do i want to try and get close to the original. I love a 5e3 with the voltages pushed but i love the sound of the old voltages to... i LOVE a 5e3! Thanks again!!

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      • #4
        Thank you Bruce! That was like sitting at Yoda's feet for me.
        It's weird, because it WAS working fine.....

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        • #5
          Originally posted by Randall View Post
          Thank you Bruce! That was like sitting at Yoda's feet for me.
          Yep you hit the nail on the head with that one!

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          • #6
            Originally posted by rockinmac View Post
            Thanks Bruce!!! This kit is a mojotone and Thanks for the Very helpful info. Is it alright to run a wire to all three pots or is that a bad idea. I plan on building another 5e3 what are your PT secondary rated at i know mojo's is a little hot. the next build i do i want to try and get close to the original. I love a 5e3 with the voltages pushed but i love the sound of the old voltages to... i LOVE a 5e3! Thanks again!!
            Yes it is quite OK to run a ground buss wire across all three pot shells... and right over to the ground lug of the closest input jack. That will be almost as good as the brass plate.
            I think you'll find using a NOS 5Y3GT rectifier tube a very good selection with the PT from Mojo Musical Supply, which is a very good kit too.
            Bruce

            Mission Amps
            Denver, CO. 80022
            www.missionamps.com
            303-955-2412

            Comment


            • #7
              I just got my 5e3 done a couple of days ago and it sounds great. But i was wonder what the current in MA should be if you take a multimeter and went from the 6v6 Cathode resistor to ground because mine is reading 162 ma. Is this right it seems a little high to me but i don't know. My plate voltage seems really good at 365 and screen at 322. Thanks!

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              • #8
                Sounds like you are trying to measure current with your meter in parallel with the cathode resistor. That will not work, you are shorting the cathode to ground, bypassing the cathode resistor. You either break into the circuit and put the current meter in SERIES, or measure the voltage across the cathode resistor and calculate the current using the formula I=V/R.
                "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

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                • #9
                  THanks. Also how much sizzle should there be in a 5e3. There isn't much on mine but it's there. and also i didn't realize this at first but when you are playing ethier channel when you turn up the volume on the other channel you get a bad hum and when there is no guitar on there is a 60 cycle hum them when you put a guitar cable with a guitar plugged in it's dead quite as long the channel you are not plugged into is off. There is just a little sizzle but it's For sure playable i compared it to my matchless lighting and i honestly like the 5e3 better if i could solve these issues. Thanks Again!

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                  • #10
                    Sounds like you have an input jack miswired or the switch in the jack is not closing to ground.
                    Bruce

                    Mission Amps
                    Denver, CO. 80022
                    www.missionamps.com
                    303-955-2412

                    Comment


                    • #11
                      Hi Bruce,

                      Thanks for that information!
                      I have a question: I will be getting a brass plate with my chassis. Which do you prefer, brass plate or no brass plate?
                      And if you prefer the plate, what then would be the best grounding scheme to use with it?

                      Thank you!

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                      • #12
                        it is real difficult to solder to the chassis itself. it is much easier to solder to the brass plate. By mounting the brass plate under the controls, it is in contact with the chassis and is considered to be the chassis electrically. So you would use the same grounding scheme either way. if you are doing some sort of star ground and not soldering to the chassis in the area near the controls, then you can leave out the plate. it does nothing but make soldering easier.
                        Education is what you're left with after you have forgotten what you have learned.

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                        • #13
                          Thanks Enzo. Yes, I was not relishing trying to get a good solder joint on that steel!

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