1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

First Build - Rob Robinette Micro Champ

Discussion in 'Shock Brother's DIY Amps' started by SJK45, Aug 14, 2020.

  1. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    This forum is amazing! Thanks everyone so much for all your help. Hopefully I'll get the remaining capacitors in the next day or two and I'll then post some pictures of the completed board.
     
    andrewRneumann likes this.
  2. James Knox

    James Knox Tele-Holic Silver Supporter

    Posts:
    657
    Joined:
    Aug 13, 2003
    Location:
    Phoenix
    Paul-T likes this.
  3. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    I think that I’ve completed the circuit board now. The soldering is pretty dodgy but I’m getting better. The next one will be quite nice!

    I’m going to check the resistances and then starting populating the chassis.
     

    Attached Files:

    Lowerleftcoast likes this.
  4. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    Hmmm - maybe I should have put the wires on after I had soldered the chassis....

    I also feel that I may have put the board too close to the power input?
     

    Attached Files:

    Last edited: Aug 20, 2020
  5. andrewRneumann

    andrewRneumann Tele-Holic

    Posts:
    593
    Joined:
    Mar 22, 2020
    Location:
    Cincinnati, OH, USA
    Looks like it’s coming along. What PT did you end up procuring? Does it have an HT center tap and/or 6.3vac center tap?

    How did the resistance measurements check out?

    Btw, what is this going in? Are you reclaiming something and need long pot shafts?

    So many questions.... ;)
     
  6. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    I ended up with the Ampmaker toroid one. We'll see how it goes.

    https://www.ampmaker.com/shop/240v-6-3v-toroid-power-transformer/

    I'm going to start wiring connecting the circuit board to the switches etc.

    The resistance readings were (target in brackets):

    Cathode V2 - 820ohms (820)
    Voltage dropping resistor 465ohms (470)
    Voltage dropping resistor 39.27 ohms (39)
    V2 Grid stopper 466.5k ohms (470k)
    V1B Cathode Resistor 1475k ohms (1.5k)
    V1 Load Resistor x 2 = 101.1k ohms and 98.5k ohms(100k)
    V1A Grid Stopper 32.5k ohms (33k)
    V1A Cathode resistor 1.476k ohms (1.5k)

    First time I've ever used a multimeter!

    Do I need to check the capacitors too?

    I'm not sure what it's going in yet - I'm going to build a custom cabinet. I'll probably cut the shafts on the pots as a final job.
     
    Last edited: Aug 25, 2020
  7. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    613
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    I hope that is a typo.

    Edit: same for the V1a cathode
     
    SJK45 likes this.
  8. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    Yes the V1B was a typo - missed the decimal! Sorry. Correct readings are:

    Cathode V2 - 820ohms (820)
    Voltage dropping resistor 465ohms (470)
    Voltage dropping resistor 39.27 ohms (39)
    V2 Grid stopper 466.5k ohms (470k)
    V1B Cathode Resistor 1.475k ohms (1.5k)
    V1 Load Resistor x 2 = 101.1k ohms and 98.5k ohms(100k)
    V1A Grid Stopper 32.5k ohms (33k)
    V1A Cathode resistor 1.476k ohms (1.5k)
     
  9. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    Some photos of the board in the chassis.
     

    Attached Files:

  10. Paul-T

    Paul-T Tele-Meister

    Posts:
    482
    Joined:
    Nov 23, 2018
    Location:
    London
    Looking great!

    How did you mount the toroid? I've read about it but don't understand it.
     
  11. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    The Toroid sits between a round rubber ring on the bottom and a round metal plate on top. The toroid is then mounted by screwing a bolt through the centre directly into the chassis. It is held tight because the bolt screws down onto the round metal plate on the top - I'll send some photos when I'm back building. I'm hoping to do most of the remaining work this weekend.
     
  12. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    Just a quick question. I don’t understand what the 6.3v to all fill is meant to look like when actually wired up. Can anyone give me any tips?

    Am I simply connecting a twisted power wires to the valves @4 and 5?
     

    Attached Files:

  13. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    613
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    SJK45 and andrewRneumann like this.
  14. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    613
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    9 is also connected to the heater wiring. The two triode heaters in a preamp tube can be connected in series and in parallel. If I remember correctly, parallel results in the least amount of hum. So 4&5 are connected to one heater wire, 9 is connected to the other.

    Screenshot_20200909-125628.png

    f stands for filament.
     
    andrewRneumann likes this.
  15. andrewRneumann

    andrewRneumann Tele-Holic

    Posts:
    593
    Joined:
    Mar 22, 2020
    Location:
    Cincinnati, OH, USA
    You’ll be daisy chaining all the tubes that use 6.3V heaters/filaments in parallel. The wisdom here is to go in order starting with the least noise critical tube and end with the input tube. That way the least amount of heater current is flowing at the terminals of the most noise sensitive tube. In your case it’s pretty obvious that you should start with the rectifier (I’m assuming you are building the Micro Champ as Rob lays it out), then wire over to the power tube, and finally the input tube. You’ll need to create 3 sets of twisted pair jumpers between the pilot light and the 3 tubes. Good luck and I hope this helps!
     
  16. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    Thanks guys that’s very helpful. I’ve just started my wiring.

    I’ve done the power sockets - I’m just mulling over how to hook up the toroidal transformer. I think because of its design it doesn’t have lugs so my plan is to hook up the two brown 0-240v power wires to the switch and then run another set of wires from the switch to the light but I’m not sure? It seems a bit clumsy but in the absence of lugs I can’t think of what else to do. B07A5B08-9D02-466B-AAA5-B16386D53F1C.jpeg

    E32C9EFB-A20E-41F1-8DA7-407155D5522C.jpeg

    https://www.ampmaker.com/shop/240v-6-3v-toroid-power-transformer/
     
    andrewRneumann likes this.
  17. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    These are the wires out of the transformer...

    7F6674EC-2668-4F77-A0C3-E40290931020.jpeg
     
    andrewRneumann likes this.
  18. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    454E2D11-6202-42CA-BDFB-66161D20A8EF.jpeg Hm - sorry another question. I presume on this diagram the headphone jack is in fact the one on the right and the labels for it are
    g= sleeve,
    S=ring and
    t= tip?
     
  19. SJK45

    SJK45 TDPRI Member

    Age:
    44
    Posts:
    43
    Joined:
    Jun 11, 2020
    Location:
    UK
    7FAC53A9-4693-4DB8-90C7-C225A034D1CF.jpeg This is how I’ve wired the headphone jack and the feedback switch. Not soldered it yet. Thanks
     
  20. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    7,960
    Joined:
    Dec 29, 2012
    Location:
    United States
    The headphone jack is on the left. TRS = Tip, Ring, Sleeve.

    The switched speaker jack is Tip, Switch (or shunt), Ground.
     
    D'tar likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.