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  1. Replies
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    Tone control issue ?

    Hello,
    I have a job in progress restoring an old Dynacord Bass-King. I just noticed the bass control is not quite functional as should be jumping to huge boost the bass after fraction of knob turn....
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    217

    I just work into a '63 Dynacord Bass-King....

    I just work into a '63 Dynacord Bass-King. Rectified alcohol and ear sticks (a lot) works for me. Be careful at any holes which are not solder sealed as the dirty liquid can leak on the other side...
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    463

    As can see there is a path to the v1 plate to...

    As can see there is a path to the v1 plate to ground through 500pF cap , so maybe big 2M resistor is matter. You can fit one 1M resistor in top of more common 1M pot and then get half of max signal...
  4. Take a look at this: GW Instek, gag-810.Analog...

    Take a look at this: GW Instek, gag-810.Analog basic one, 200 bucks around, very happy with it.
    https://www.gwinstek.com/en-GB/products/detail/GAG-810_GAG-809
  5. ...btw talking about speakers...something for...

    ...btw talking about speakers...something for mythbusters..:)

    https://m.youtube.com/watch?v=P4grDEC_Uj0

    https://m.youtube.com/watch?v=CDy2dwPQAFs

    https://m.youtube.com/watch?v=GIjyiIjvXFk
  6. I don't think they made transformers, but they...

    I don't think they made transformers, but they received transformers from one of their suppliers. I.m pretty sure no one supplier ship to Marshall transformers like that but pretty much well packed...
  7. Those screen draw (sometimes) current at...

    Those screen draw (sometimes) current at startup...a lot, why ?
    I asked just to share opinions about possible scenarios by the other techs experience as for me no one power tubes I used till now...
  8. ..and Yes, it was confirmed. It is a bad tube. I...

    ..and Yes, it was confirmed. It is a bad tube. I swapped it to the other side of the rail. After some successful starts up yesterday, today it was time to smoke its 1k/ 5w screen grid resistor into...
  9. ....like this ? :)...

    ....like this ? :)
    https://m.youtube.com/watch?v=_2raNqztPX0
  10. Thanks, I will swap it on other position and...

    Thanks, I will swap it on other position and hope to confirm the tube is bad.
  11. Most probable reason for screen resistor burning

    Hello,
    I recorded a issue to one of my power tube from a new 6CA7 matched set. At start up one of the screen resistor it start to burn. It is happen just at first startup after the amp stayed off...
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    2,737

    It is something which intrigues in Rod Elliot...

    It is something which intrigues in Rod Elliot floating paraphase description , as: "The second form is shown shown below (version 2), and it works by using the second valve as a unity gain inverter,...
  13. The "wattage" is expression of power and is...

    The "wattage" is expression of power and is related by the heat dissipated by the speaker coil in You instance. You have to determine this as maximum admissible condition. Maybe some guys know how...
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    2,737

    That is correct

    That is correct
  15. Replies
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    2,737

    Sure, I.ll need to do the amplification of...

    Sure, I.ll need to do the amplification of paraphase more than unity by a factor. That meant less local feedback. In consequence the feedback resistor should be bigger, That is correct ? I used 470k...
  16. Replies
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    2,737

    Can be introduced in simulation a build-out...

    Can be introduced in simulation a build-out resistor to balance the output impedance as M Blencowe suggested, please?
    ...
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    512

    It,s a "splitted" PT secondary, as well can run...

    It,s a "splitted" PT secondary, as well can run the amp in class B operation with max voltage the tubes can handle( think 800V to EL34) but keeping screens to a safe 400V. See old sixties Dynacords...
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    double post , sorry

    double post , sorry
  19. Replies
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    2,737

    Latest news. Before leaving the house I still...

    Latest news.
    Before leaving the house I still found some time to modify the bias circuit as in picture below, as it was suggested:

    55139

    Now the amp is absolutely quiet. Zero noise, none.
    I...
  20. Replies
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    Thanks for You good intentions but in two hours...

    Thanks for You good intentions but in two hours have to go at work, I.m very sorry must I leave You. Thanks for support gents. Have a nice week!
  21. Replies
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    2,737

    It is not, take a look at the pics in post 95

    It is not, take a look at the pics in post 95
  22. Replies
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    2,737

    No , there is one cap which goes to second triode...

    No , there is one cap which goes to second triode grid, This was changed. The couplings to power stage are the same 47nf
  23. Replies
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    I posted wrong pics from rush, Now there are the...

    I posted wrong pics from rush, Now there are the right one , Sorry.
    I just changed the capacitor between first and second triode 47nf and 470 nf. Didn't see any changes
  24. Replies
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    470n 55137 47nf 55138 This was picked...

    470n

    55137

    47nf

    55138

    This was picked up with ground clips to chassis. Previous was with ground clips floated, and also I used a digital filter to smooth the traces.
  25. Replies
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    No, this was done with ground clips floated,...

    No, this was done with ground clips floated, seems it is not right. Post other pics in minute
  26. Replies
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    The source of noise is the ripple from bias...

    The source of noise is the ripple from bias supply as it was confirmed. The problem is why is not cancelled in power stage. Is not a subject of any ground loops as it is very simple, but I.ll check...
  27. Replies
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    Ok, I tied the inverter back to power grids and...

    Ok, I tied the inverter back to power grids and this is what I get in differential mode:

    This is with 47nF interstage

    55131

    This is with 470nF interstage

    55132
  28. Replies
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    Are You talking about interstage between first...

    Are You talking about interstage between first stage and paraphase ? Couplings between inverter and power grids ? Or both ? Thanks

    The traces in post 79 was done without Pi coupled to the grids....
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