Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Not sure if 12ax7 was wired up properly

Discussion in 'Glowing Bottle Tube Amp Forum' started by Stevi q, Sep 18, 2017.

  1. Stevi q

    Stevi q Tele-Meister

    Age:
    45
    125
    Aug 30, 2016
    bayshore,Long Island,new york
    In the pics you can see the wire from the volume etc goes to Pin 2 on the first 12ax7.Then pin # 1 sends the output signal over to the first lug on the terminal strip where you see the round orange cap.I have signal there .I can follow the signal into pin 7 of the opposite Side of the 12ax7 ,however nothing comes out the output.you can see the output or 6th pin of the 12ax7 goes to the opposite terminal strip as pin 1,& there is a resistor between them .All the resistors work.so I don't get any signal coming off the output of the second half of the v1 12ax7.You can see there is a wire connecting that output of the 2nd half of the 12ax7 to
    The second 12ax7 .I jumpered the Input on the second side of the 12ax7 to the wire that goes to the second 12Ax7 valve 2,then I get the amp to run just fine .Tremolo works.
    The first Side of the 12ax7 has 60 volts the second plate has nothing ,zero volts.I notice that pin 2 sends the signal to pin 1 inside the tube,so why doesn't it do that for pin 6 to 7.I with care wiggled the tube to see if it was loose on the socket .Seems good to me .Didnt make any noises when I moved it.is this wiring correct?thanks for your help.
     

    Attached Files:

    Last edited: Sep 18, 2017

  2. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    The second plate (pin 6) must have voltage to run so trace backwards from pin 6 to find out why it doesn't have a voltage supply.
     

  3. Stevi q

    Stevi q Tele-Meister

    Age:
    45
    125
    Aug 30, 2016
    bayshore,Long Island,new york
    See where the the second output screen is and where it is connected to
    Thanks for the reply man.I used this probe I built that sends the signal from the amp your working on to a separate amp so you can determine where the signal is and isn't .I have the signal going up to the pin 7.when I put my probe on the 7th pin the output ,I get no signal at all.I am new to all this stuff .I noticed that the first half of the 12ax7 the signal goes from pin 2 and then out of pin 1 .Isnthe same for the other half?So does pin 7 input connect to pin 6 output through the tube like it does with pin 1,&2.I have changed the 12ax7 tube for a couple of others with same result.Does this mean my socket is somehow not passing the signal?Thanks for your help man.
     

  4. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    The "B" triode cannot pass a signal without voltage on pin 6 (plate). Trace from pin 6 with your multimeter in DC volts mode toward the power supply to find the break in the power supply.
     

  5. Stevi q

    Stevi q Tele-Meister

    Age:
    45
    125
    Aug 30, 2016
    bayshore,Long Island,new york
    There is a resistor that is inbetween the 300 volts coming from the capacitor and the plate on the second half of the 12ax7 pin 6. That resistors colors have been darkened way more then the other resistors with the the same color bands.That plus I am getting 300 volts on the one side and I am getting zero on the other side that is closest to the plate.says it is a 390k resistor.I thought I would see a physical look to the damage other then darkening.Very cool to learn that today.Do you know if I can play with that value a bit or just stay with that.I am going to solder a new resistor in place a little bit later today.It has to be that.Thanks so much for the help.I needed that guidance on how to trouble shoot this.I will post what happens .pics showing my chopstick pointing to the resistor.I thought I w
     

    Attached Files:


  6. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    41
    Mar 1, 2010
    Kent, OH
    Make sure pin 8 (V1B cathode) has a resistor to ground, and a voltage (should be about 1.5-3 volts) as long as this is a normal gain stage at least. Try a 100k plate resistor to pin 6 (that's a good place to start). You should see signal at pin 6 if you are feeding signal at pin 7.

    [​IMG]
     

  7. Stevi q

    Stevi q Tele-Meister

    Age:
    45
    125
    Aug 30, 2016
    bayshore,Long Island,new york
     

  8. Stevi q

    Stevi q Tele-Meister

    Age:
    45
    125
    Aug 30, 2016
    bayshore,Long Island,new york
    Thanks man.I have 390k plate resistors .that gives me 60 volts to the plates.I Definately am gonna try 100k.I found a plate resistor that had 300 volts on the one side and the side towards the plate didn't have anything .I am replacing that in a little while .I am grateful that I have a replacement here already.take care
     

  9. Stevi q

    Stevi q Tele-Meister

    Age:
    45
    125
    Aug 30, 2016
    bayshore,Long Island,new york
    Yea man that resistor that I traced the b+ to on one side but not the other was the problem.This amp is loud.Now I have to crank it up too loud to get that overdriven sound .I can't do that while I am living in a apartment.I swear I was enjoying the sound of the 1 half of the 12ax7 with out the other being on too.I was loving that sound .now the walls are trembling to get that same overdriven tube sound.Maybe a mod etc..iI appreciate your help BIGTIME .Very happy .take care
     
    robrob likes this.

  10. Silverface

    Silverface Poster Extraordinaire Ad Free Member

    Age:
    65
    Mar 2, 2003
    Lawndale CA
    1. What amp are you working on?

    2. "mods" are not a great idea until you really understand how the basics work. Don't change anything until you understand the signal path, the power rail (where you seem to be confused) and ground schemes. In a true PTP amp like that there are not simple "packaged" mods - you have to clearly understand what's going on *now* to grasp what a mod will do. You seem a bit confused as to why the amp has more headroom now that the preamp is operating as designed. Get all that figured out from a theoretical standpoint first, and then determine if any"mods" are even advisable in that specific amp. Many create undue current loads, change voltages in undesirable ways for certain amps etc. etc.
     

  11. Stevi q

    Stevi q Tele-Meister

    Age:
    45
    125
    Aug 30, 2016
    bayshore,Long Island,new york
    Hey silverface .This is a that no name ,no schematic amp that I found being thrown out to the garbage.I really had a fun ,crazy time bringing her back to life .I built a probe with a cap in it for safety ,and that helped a lot .Along with the multi meter.I am just starting understand how Amps work.Having the other half of the 12ax7 boosting the signal really made it loud.I wanna install a 1/4 in jack for the speakers so I can run a power attenuater.I appreciate your advice,and your time .Take care man ,I will see ya round the forum.Stevi
     

  12. Stevi q

    Stevi q Tele-Meister

    Age:
    45
    125
    Aug 30, 2016
    bayshore,Long Island,new york
    I found a 18 watt Marshall schematic that is very similiar to what I have .Even though it's a no name ,no schematic amplifier ,you can still find a similar schematic.I love this found at the curb going to the dump guitar amp.It really has a great sound.The last problem was a resistor that didn't look damaged.it did have faded band colors .The resistor read 300volts on one side and it read -450 n the other side .that was it replaced it and bam,she came on.The first issue was vintage wired el84 tube sockets.pin 1 instead of pin 2.There was a bunch of other stuff too like caps,soldering joints re flowed etc.What a fun project.thanks everyone who helped on this .stevi q
     

  13. Stevi q

    Stevi q Tele-Meister

    Age:
    45
    125
    Aug 30, 2016
    bayshore,Long Island,new york
    Here she is before I cleaned her up.I haven't put her back in the cab yet.The front panel was cleaned after this picture ,and now it looks almost new.
     

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  14. zook

    zook Friend of Leo's

    Aug 6, 2003
    Cochise, AZ
    I don't see a heater connection between pin 4 and pin 5. There is a wire going to pin 4, but I can't see that connection to pin 5
     

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