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.

Trem and basic circuit help

Discussion in 'Shock Brother's DIY Amps' started by ejb222, Sep 15, 2015.

  1. Fred Mertz

    Fred Mertz Tele-Afflicted

    Posts:
    1,440
    Joined:
    Nov 11, 2011
    Location:
    Indiana
    Well you had several suggestions to look at the AA764 circuit that you ignored, as in did not respond to. Something to the effect of thanks, but no thanks, I want to pursue this other circuit would have been nice.

    Above you asked about what to do with the unused triode. If you looked at the AA764 circuit, you would have your answer.
     
  2. ejb222

    ejb222 Tele-Holic

    Posts:
    616
    Joined:
    Jul 12, 2008
    Location:
    Massachusetts
    I did take a gander at that circuit. I'm sorry you felt as though I ignored you. I think I was most motivated to use only one triode for the trem circuit and for some reason have it in my mind that feeding the circuit into the grids of the output tubes was more simple. I'm likely wrong as I obviously don't know much about tremolo circuits yet. I also remembered that the Reverberocket II had a decent tremolo that used the same tube I already own. So I think that also steered me away from the AA764.
    Maybe it was a bad decision...I guess I'll find out.
    I do appreciate the help and pointing me in the direction to continue to look for working circuits. Again sorry, I did not intend to ignore your advice.

    If you don't mind my asking another question. Does the second triode of the AA764 trem circuit serve to complete the 360 phase shift?

    OK maybe 2 questions...I've notice a lot of trem tubes running at voltages above the gain stage voltages?...actually voltages seem to be the same as the screen grid voltages.
     
  3. Fred Mertz

    Fred Mertz Tele-Afflicted

    Posts:
    1,440
    Joined:
    Nov 11, 2011
    Location:
    Indiana
    The first triode is a low frequency oscillator (LFO) that generates a sine wave type of voltage signal. There is no phase shifting performed. The second triode is a cathode follower. The cathode follower is able to drive low impedance loads with negligible signal voltage loss. The signal when applied to the cathode of the second gain stage triode, in the AA764 circuit, modulates the bias of the tube with the LFO signal.

    The gain stage B+ supply needs filter separation from the tremolo B+ supply to maintain stability. That is why the tremolo tube typically has a higher B+ voltage.

    FWIW, it would be very simple to just add the AA764 tremolo to your existing amp.
     
  4. ejb222

    ejb222 Tele-Holic

    Posts:
    616
    Joined:
    Jul 12, 2008
    Location:
    Massachusetts
    Do you guys mind taking a peek at this for errors? Do you think there will be an issue with the grid stoppers placed so close to the plate resistors? With parallel output tubes, is there a best practice in layout as to minimize the number of wires crossing each other?
     

    Attached Files:

  5. ejb222

    ejb222 Tele-Holic

    Posts:
    616
    Joined:
    Jul 12, 2008
    Location:
    Massachusetts
    I've got the amp put together except for the trem circuit so as to solidify one thing at a time and limit my errors so to speak :p
    I've checked some voltages...can anyone let me know if these 6V6s seem a bit off?

    Plate to Cathode = 330V
    voltage across 250R cathode resistor(shared by 2 6V6s) = 22.5V
    Plate to ground = 365V

    According to https://robrobinette.com/Tube_Bias_Calculator.htm I'm at about 14w plate dissipation and 45mA cathode current per tube
    This seem like too much?
     
  6. Wally

    Wally Telefied Ad Free Member

    Posts:
    38,742
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    What tubes? If you have tubes with. Max plate dissipation of 14 watts, the you are dead on with 100% of MPD. If you have 12 watt tubes, then your plate dissipation is a bit high at 116% or so....one could try a 270ohm resistor to see what happens. Using those voltages, which will change a bit with a re biasing by the new resistance, the plate dissation comes to about 108%.....but one would want to take the measurements with the new resistance to see what is actually there.
     
  7. ejb222

    ejb222 Tele-Holic

    Posts:
    616
    Joined:
    Jul 12, 2008
    Location:
    Massachusetts
    I'm thinking I might do that. I rechecked my measurements with a better meter. I noticed that pin 4 to ground is 370V and pin 3 to ground is 355V
    This is not desirable, correct? The B+ drops over 15V through the OT as it goes to pin 3. Is that typical voltage drop through the OT? Its an EDCOR GSXE 10-8-5K. I measured the resistance of the primary at 186R. So 15V/186R = 80mA.

    Oh and I'm currently testing with one Hammond 6V6GT and one FM.Co 6V6GT in parallel....I assume they are both likely RCAs?
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.