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.

5e3: 310vac Pt

Discussion in 'Amp Tech Center' started by itsa68, Mar 16, 2016.

  1. itsa68

    itsa68 Tele-Meister

    Posts:
    163
    Joined:
    May 17, 2011
    Location:
    Chicago
    My very first point to point build! Assembled with painstaking attention to detail. All joints are tested for continuity and measure well. Upon firing up, it sounded gritty and sputtery like a dead battery. Upon checking suggested b+ voltages, I now see that the power transformer is putting out 310vac on the secondary and 305~vdc after rectification. Apparently, 5e3's are supposed to run at around 350v b+. Explains the sputtery sound! Ah well, live and learn.

    This PT was used in a stereo amp with two pairs of 6v6's, so I assumed it would power one push pull pair just fine. Is there a way to adjust the arrangement to use this PT? Or do I just need to buy another tranny?

    Thanks for the comments. I have a friend who is wondering if things would work out if I adjusted the bias and then reduced the resisters to the preamp tubes.

    Here's a photo of my glowing project :)
    [​IMG]
     
  2. muchxs

    muchxs Doctor of Teleocity

    Posts:
    13,171
    Joined:
    Aug 14, 2004
    Location:
    New England
    1950s tube data sheets specify around 300 volts on the plates of 6V6 tubes. The tweed Deluxe is a virtual rip of the AB1 circuit spelled out in RCA's tube data sheet from the era... except that original tweed Deluxe transformers are approximately 350v-0-350v with 117v at the wall.

    It's possible your point to point layout is self- oscillating. That tends to drag down the supply voltage while sounding ratty and loose.

    If you change the PT, I'll be happy to get the salvage.
     
  3. itsa68

    itsa68 Tele-Meister

    Posts:
    163
    Joined:
    May 17, 2011
    Location:
    Chicago
    How would I check if this circuit was oscillating?
     
  4. andyfromdenver

    andyfromdenver Friend of Leo's

    Posts:
    4,703
    Joined:
    Dec 21, 2011
    Location:
    grandpa's
    yes, i wouldn't necessarily rule in the PT from the info provided.
    check all pins voltages (the relevant) and report. you could have a miswire. if your pwr section is severely underbiased (or is it overbiased? terminology...) with an accidental 4.7k, for example, your amp will sound very sputtery and low vol.

    when all is well, and you only wish to raise the B+ switch to solid state rect or try a gz34, the mighty GZ34
     
    Last edited: Mar 17, 2016
  5. itsa68

    itsa68 Tele-Meister

    Posts:
    163
    Joined:
    May 17, 2011
    Location:
    Chicago
    Out of town until the weekend. Will measure pins and report when I return. I did measure everything last night and saw that each point was about 30v under what it should be. That's to say that every point was consistently under powered.

    I think I have a GZ34 around somewhere...
     
  6. itsa68

    itsa68 Tele-Meister

    Posts:
    163
    Joined:
    May 17, 2011
    Location:
    Chicago
    Thought: if I remember correctly, my 6v6 plates were getting around 280v. If I reduce the power resistor between the first two filter caps, I should be able to raise that voltage up to 310v. And since the output transformer was originally matched with the PT, it should run fine on a 310v center tap.

    Does this sound correct?

    As an addition, this spec sheet lists plate voltages for 6v6's at between 285v in push pull and 315v single ended: http://www.r-type.org/pdfs/6v6g.pdf
     
    Last edited: Mar 17, 2016
  7. Wally

    Wally Telefied Ad Free Member

    Posts:
    37,845
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    It would be of value to have a complete voltage chart for the entire circuit...all tubes. It would be of value to know how those power tubes are biased.
    As muchxs' suggestion that he would gladly relieve you of that salvage PT indicates, the PT is more than likely not your problem. It is yielding 'ideal' voltages for those 6V6's......even though very few guitar amp designs have held to those tube specs.
     
  8. dankilling

    dankilling Tele-Afflicted Silver Supporter

    Posts:
    1,491
    Joined:
    Oct 28, 2014
    Location:
    Lehigh Valley, PA
    What rectifier tube are you using? Instead of changing the circuit to get more voltage, I would roll a few different rectifiers through to see if you can get where you want. If you're running a 5ys, maybe try a GZ34 or a 5u4 if the PT can handle the heater draw?
     
  9. itsa68

    itsa68 Tele-Meister

    Posts:
    163
    Joined:
    May 17, 2011
    Location:
    Chicago
    This PT originally ran a 5u4. I'll try that soon. Currently using a 5y3gt.

    I'm still wondering if dropping that first 5k resister would do the trick.
     
  10. dankilling

    dankilling Tele-Afflicted Silver Supporter

    Posts:
    1,491
    Joined:
    Oct 28, 2014
    Location:
    Lehigh Valley, PA
    The 5u4 should give you another 20 or so volts, GZ34, would be about another 50 or so. A solid state plugin should give about 60v, so lots of choices to play with to get you into whatever range you're looking for. Have fun!
     
  11. mozzman

    mozzman Tele-Meister

    Posts:
    159
    Joined:
    Nov 2, 2015
    Location:
    NEPA
    Pull the output tubes, measure plate voltage, how much higher is it?
     
  12. Wally

    Wally Telefied Ad Free Member

    Posts:
    37,845
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    Current draw and B+ voltage are linked. Without knowing the bias situation, one doesn't really have all of the information needed. I am going to doubt that those 6V6's are pulling really high current....but what if they are??? Mozzman's suggestion of pulling the power tubes and measuring the B+ would be a clue to the effect of whatever current draw is there has on that B+.
     
  13. itsa68

    itsa68 Tele-Meister

    Posts:
    163
    Joined:
    May 17, 2011
    Location:
    Chicago
    Understood. Thanks for the explanation, that's helpful.

    Will measure as soon as I return home.
     
  14. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    8,142
    Joined:
    Dec 29, 2012
    Location:
    United States
    No, that power resistor sets the voltage for the 6V6 screens, not the plates.

    Like the others have said I don't believe your sputtery problem is voltage related, something else is wrong with the amp.

    Show us all your tube pin voltages and the voltages at the filter caps (B+1, 2 and 3).

    If you do end up wanting more voltage a GZ34 or even solid state diode rectification will boost it.
     
  15. itsa68

    itsa68 Tele-Meister

    Posts:
    163
    Joined:
    May 17, 2011
    Location:
    Chicago
    alrighty, here are my measurements. Got some time to work on hobby stuff this week, so hoping to get lucky with troubleshooting.

    Without a rectifier:
    310 VAC

    With only the rectifier tube:
    B+1: 414 VDC
    B+2: 409 VDC
    B+3: 403 VDC
    6V6 pin 4: 415 VDC

    With all tubes plugged in:
    B+: 320 VDC
    B+2: 288 VDC
    B+3: 225 VDC

    6V6 pin 4: 290 VDC
    6v6 bias pin 8: 17.5 VDC

    first 12ax7 pin 6: 145 VDC
    first 12ax7 bias pin 8: 1.3 VDC

    second 12ax7 pin 1: 152 VDC
    pin 3: 1 VDC
    second 12ax7 pin 6: 190 VDC
    pin 8: 37 VDC

    In my limited understanding, things look pretty normal. Please let me know if there's something i'm not seeing here, but my suspicion is that with a rectifier which passes more current, I should see a general improvement as every stage seems underpowered

    EDIT: plugged it in with a 5u4, same problems still. open to all suggestions, I am willing to do my homework and learn :)
     
    Last edited: Mar 21, 2016
  16. itsa68

    itsa68 Tele-Meister

    Posts:
    163
    Joined:
    May 17, 2011
    Location:
    Chicago
    Also as far as sound quality, the amp is noisy and had an octave down sound mixed in with the dry signal. It is distorted at all settings.

    The volume control adds a lot more noise, so I at least know that some of the noise is coming from the first gain stage.

    Finally, here is a useful tool I've been using as a loose guide. Trying to "ballpark" to these voltages:
    [​IMG]
     
    Last edited: Mar 21, 2016
  17. dankilling

    dankilling Tele-Afflicted Silver Supporter

    Posts:
    1,491
    Joined:
    Oct 28, 2014
    Location:
    Lehigh Valley, PA
    Can we get a video or some sound clips of the amp? Ghosting (the octave down) can come from a few different things, but combined with the overall distortion and noise you're experiencing, I'm wondering if you have a bad filter cap, or if one of your power tubes isn't being properly fed voltage. Are you measuring both 6v6's at the tube, or are you doing it at the board? Finally, what is your first preamp tube? Your voltage chart says they are both 12ax7's which can also force a 5e3 into distortion pretty fast. A 12ay7 is preferred in the stock circuit to lower the chance of nasty blocking distortion.
     
  18. itsa68

    itsa68 Tele-Meister

    Posts:
    163
    Joined:
    May 17, 2011
    Location:
    Chicago
    I rewired the 6v6 pin 4 so that each wire reached back to the b+2 junction point, because I had daisy changed them before and theorized that the second 6v6 was probably underpowered when the first began taking current. It cleared up some of the "ghosting" affect, but the amp is still always distorted, so I will keep on :) I am thoroughly enjoying the process of troubleshooting because I'm learning a lot about this amplifier.

    Here is a short video which illustrates the sound. I have played a number of original 5e3 amps, and none of them have had this type of decay.
     
  19. itsa68

    itsa68 Tele-Meister

    Posts:
    163
    Joined:
    May 17, 2011
    Location:
    Chicago
    Also, I am measuring all voltages from the tube pin.
     
  20. Telenut62

    Telenut62 Poster Extraordinaire

    Age:
    60
    Posts:
    5,592
    Joined:
    Oct 29, 2008
    Location:
    Eugowra, Australia
    Bad solder joint.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.