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.

Transformers for Ceriatone Overtone Special (Dumble Overdrive Special clone)

Discussion in 'Shock Brother's DIY Amps' started by itsGiusto, Nov 22, 2020.

  1. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    652
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    Ah, I'm suddenly worrying if the PT I got is good for this... Unfortunately I'm uncertain what the b+ current draw of this amp will be. But the JTM45 PT I got says that it's only rated for 150ma current draw on the main winding:
    http://www.classictone.net/40-18054.pdf

    Unfortunately, I chose it for the 690v, and didn't pay attention enough to the current rating. I had heard that EL34s draw more current than 6L6s, so I thought it'd be okay, but now that I'm looking into it, it's possible that EL34s only draw more current on the filaments, so I'm uncertain about the main winding. And a lot of the Fender-style 6L6 PTs I'm seeing are rated for at least 200ma on their b+ winding, if not more, so maybe this wouldn't be enough, not sure.

    Is there a way I can determine whether this will be enough?

    Update:
    Ceriatone's published voltages indicate that the main current running through each 6L6 is ~35ma (the voltage on pin 1 is 35mv, and there's a 1 ohm resistor to ground from that pin). And I assume that the 6L6 tubes are going to be the largest current draw in the amp by far. So maybe it's okay. Then again, it's only drawing 35mv at idle, probably when playing it's going to be more.

    Can anyone verify if my thinking is correct on this?
     
    Last edited: Dec 11, 2020
  2. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,648
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    I see now the Ceriatone folks went a totally different way on that. My mistake.

    Typically this footswitching is done on only 3 wires (TRS) without having to send anything hot out to the footswitch, the LED's play a role in that solution.
     
    itsGiusto likes this.
  3. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,648
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    I would prefer something bigger personally, 180mA-200mA -- this is not an amp where you want transformers "in the way".

    You get more voltage sag with the smaller PT. The net effect is you get less clean power from your 6L6's, I reckon you are building a 40W amp with this PT? Just a guess. If you are used to a 50W version of this amp you would definitely notice the earlier breakup.

    Let's say you decide to go buy another PT, is there a higher rated one that will fit the chassis you have?

    Unless you are insistent upon getting all 50W of clean power out of this amp, I'm not sure it's too a big deal for ya.
     
    Nickfl and itsGiusto like this.
  4. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    652
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    I actually ended up messaging Nik. His reply was that the b+ winding "can be 150-200mA". So maybe this transformer is good enough?

    On Ceriatone, this is labeled as a 50W amp. But I certainly don't need headroom, I'll probably exclusively play this amp with an attenuator. I'm just worried that it'd change the tone or feel of the amp - I'm just trying to build this amp so I can understand what a Dumble ODS is supposed to be like, since I've never played one, so I want it to be very close in tone and feel. But like you said, if I'm not running it all-out most of the time, it sounds like maybe it might not make a big difference?

    I'm uncertain if there's a better PT out there, and I'm open to suggestions. Certainly Mercury Magnetics has one, tailor made for this amp, but it's over $300! I refuse!

    Classictone has this one:
    http://www.classictone.net/40-18042.pdf
    It has the right voltage. Its rating is 450ma, which sounds like overkill. It doesn't have the 5v winding for the relays, but that's not the end of the world, since I have that external 6v transformer I could mount, if I found the space for it. I'm not certain where it'd safe to mount the additional transformer so it won't cause interference with the other transformers, audio cables, or anything, not certain if I'd need to be careful about that.
     
    sds1 likes this.
  5. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,648
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    150mA is plenty in terms of electrical ratings, you will not be generating any significant heat that would lead to premature failure of the transformer. That is what Nik is saying.

    The PT selection is more about power amplifier performance now. The 6L6 power amp will perform differently with a PT rated at 150mA versus 200mA. The 150mA PT will result in less clean headroom than the 200mA PT. You would notice this side by side with another 50W amp. At home with nothing to reference, I honestly don't think you will notice or care.

    If you are worried about tone and feel, lose the attenuator! :)

    You won't need the attenuator IMO, the master volume on these amps are great. You don't need a ton of power amp coloring to make an ODS sound good, clean or dirty. You can run the master volume on 2 and it will sound badass. You will be installing a bright cap across the MV pot, this is part of the reason why the MV works. You can tweak that cap for more or less bright bypass, the loss of perceived highs is, apart from power tube color, the reason why MV's tend to make things sound kinda lame. But the bright cap helps that along.

    Don't blame you there, I don't spend MM money on transformers either.

    I'm not looking at the world of choices, but I do know you will have a hard time finding Fender-type HT rating with Marshall-size cutouts without going to a Twin PT which:

    Exactly. Not ideal. But you want a PT that will not get "in the way", there you go haha. :)
     
    Pick_n_Strum, Nickfl and itsGiusto like this.
  6. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    652
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    So what's your opinion? Should I get the Twin one or not, if I don't care too much about clean headroom, but do care about tone and feel? Will the PT I have be too "in the way"?
    I also worry that the Twin PT will be crazy heavy!

    Yeah, you might have a point there. But I've always had good results from using attenuators.
    But granted, I've almost always used older-style non MV amps that you want to run at the edge of breakup (50w Plexi, Marshall 18 Watt, AC15, Tweed Champ etc). It sounds like the ODS is more designed to be able to get its signature sounds without needing to do that, because it has a dedicated preamp tube overdrive circuit. The overdrive comes mostly from the preamp, not the poweramp, maybe?

    Another reason I tend to use an attenuator is simply for safety sake. I actually don't have a 2x12, or any speaker configuration that can handle more than 25 watts (I'm working on building a 2x12 external cab right now), so I run my amps into a 1x12, and use the attenuator to make sure I'm at least cutting my amps down to where the power handling is safe for the speaker.
     
  7. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,648
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    I think given all factors and circumstances, you stick with what you have.

    I think you are giving up some output power (clean headroom) with this decision, and in a bedroom setting I think this is fairly inconsequential.

    I built a 2x6L6GC amp once with smaller transformers, you don't tend to notice this kind of thing until you try to compete with a 50W amp. In a room by itself it will still be very loud and very clean.
     
    itsGiusto likes this.
  8. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    652
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    I've now gotten and begun to assemble the amp. I've tested using their supplied 12v relay with the Ceriatone voltage doubler circuit and the supplied 12v regulator, and surprisingly, my 5v winding on my PT actually works for this! This is a small win, but still a win, because I won't have to make my own circuit and do my own filtering, I can just rely on their board.

    But I'm a little confused why this would be. The 5v winding I have is giving out ~5.25vac. But when I run it through the voltage doubler circuit, it actually gets more than doubled, it reaches all the way to something like 13v dc! With the regulator attached, it regulates it down to something like 11.9v dc, and with the relay attached, this sags a little bit to something like 10.5v dc, which still seems to be within the cutoff range of the 12v relay to work (their datasheet here indicates that it'll work with only 75% of rated voltage, which is 9v, if I'm reading it correctly).

    So while I'm happy, I'm still looking for an explanation of why this would work with my 5v winding. And why is the voltage doubler doing 2.5 times the voltage, not just doubling?



    Update: while typing this out, I think I figured it out. The winding is giving out 5.25vac, which when rectified will be something like 7.42v dc. This, not the AC value, is getting doubled to 14.85v, and the two diodes subtract ~1.4 v in total, bringing it down to about 13.4v, which is enough to power the regulator and relay.
    Is this correct? Does it make sense?

    The only other thing I'd like to know now is, is it possible that the 5v winding, which is entirely isolated and by itself on its own winding, will sag in voltage further when the amp is in full use? Will the increased current pull on the main b+ winding affect this separate winding, causing it to sag below the 9v threshold? Or are separate windings completely unaffected by each other?
     
  9. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,648
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    This right here, the windings are isolated from each other.

    If you take the diode drops off the top, you get closer to your actual results:

    2* ((5.25 * 1.4) - 1.4) = 11.9

    (just doing the math in different order here, so that the VDC dropped by the diodes is not doubled)
     
    itsGiusto likes this.
  10. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    652
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    Thanks!

    But I was actually seeing over 13v after the voltage doubler. It was only after the output of the 12v regulator that I was seeing 11.9v
     
    sds1 likes this.
  11. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,648
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Oh OK, well either way you are correct that you're doubling the DC so the result is more than a factor of AC x 2

    I think maybe you pull that 7812, as you noted with your readings the voltage regulator isn't regulating (a regulated voltage supply within spec doesn't sag). This is likely due to the fact that you are not meeting the dropout voltage requirement of the regulator, which you can see from the datasheet is typically 2V:

    https://www.hobbytronics.co.uk/datasheets/L7812.pdf

    Dropout voltage is the DC "headroom" you need to give the 7812 to do its job. So a minimum of 14VDC input in this case.

    If you pull the 7812 I reckon you'll observe the power supply behaves exactly the same as it does now.
     
    Pick_n_Strum and itsGiusto like this.
  12. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    652
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    I just tested this setup again, but using both relays, instead of just one. I wanted to make sure that having both relays on at the same time wouldn't cause the voltage to sag more, and result in the relays not working correctly. It did end up working just fine with both relays on. The strange thing is that with both relays on, the voltage coming out of the regulator did not sag any more - it was still at around 10.5v at the output of the regulator, which is the same as it was with only one relay on.

    If it were voltage sag, then adding additional current draw should have caused it to sag more, right? So maybe the reason why it's 10.5v coming out of the regulator isn't because of sag, but because of something else?
     
    Pick_n_Strum likes this.
  13. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,648
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Or, maybe the 7812 is regulating 10.5VDC under those conditions?

    I guess it makes sense if you were short on input it wouldn't just do NOTHING.
     
    Pick_n_Strum and itsGiusto like this.
  14. Pick_n_Strum

    Pick_n_Strum Tele-Meister

    Age:
    31
    Posts:
    133
    Joined:
    Sep 28, 2016
    Location:
    Lino Lakes, MN
    Love the info coming out of this thread on relays. Makes me wish I had hooked mine up and tested them outside the circuit before throwing them in - just for fun of course.

    I'm curious what your testing setup is itsGiusto. Are you just sending your supply voltage through the rectifier / doubler circuits and then feeling for a click on the relay?
     
    itsGiusto likes this.
  15. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    652
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    Yep, that's my first step. But after that I'm also using my DMM's continuity mode to beep when there's an electrical connection, and testing each pin on the relays to make sure they're doing the right thing, that they're disconnecting/connecting when they should.
     
    Last edited: Dec 16, 2020
    sds1 and Pick_n_Strum like this.
  16. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    652
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    Okay, new update for the relay stuff.

    I've hooked it up inside the chassis, now. The 5v winding does work for the 12v relays, as I mentioned before. However, it doesn't work consistently enough. Sometimes, there's a bit of a delay between switching it and the relay engaging - I'm guessing that this is because the voltage sags below 12v as mentioned earlier, to about 10.5 volts sometimes, and who knows sometimes maybe it goes even lower.

    To remedy this, I'm going to get these 9v DPDT relays and 9v regulators which I think should just be a drop-in replacement for the 12v regulator and 12v relays that came with the kit:
    https://www.amazon.com/gp/product/B0874MMY9M/?tag=tdpri-20
    https://www.amazon.com/gp/product/B07RZBBRVV/?tag=tdpri-20

    Hopefully that'll provide enough headroom that I won't get the delayed switching.

    Update: I actually think I was incorrect about this, I think the problems were being caused by two lugs on the switch sometimes shorting. I rewired the switch, and it seems to be doing much better with no delayed switching. We'll see, hopefully I won't need the 9v relays.
     
    Last edited: Dec 24, 2020
  17. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    652
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    Hey all, I finished the build last week. Here's the final product:
    [​IMG]

    Pretty happy with it so far. Though I do think I should probably get a traditionally Dumble-y speaker, maybe a Celestion G12-65 style speaker. Been playing it through an alnico blue for now.
     
    FenderLover, sds1 and 2L man like this.
  18. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    652
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    Some gut shots

    Main amp:
    [​IMG]
    [​IMG]
    (the red and yellow transformer wires were still unsoldered at this point)

    Dumbleator:
    [​IMG]
     
    sds1 likes this.
  19. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,648
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    omg really nice work!!

    Check out the Warehouse ET-90 if you haven't already, a lot of the D builders are using the ET-65 and ET-90, I have tried them in different amps and they are my favorite speaker. But also they are pretty cheap. If there are better speakers for more money I don't want to know! Seriously though, the ET-65 and ET-90 (and I'm trying ET-10 right now as well) are really great for D-style especially.

    Also I know you plan to keep this thing low, but ideally you want closer to 100W speaker to handle the peak output of the 50W rated amp. 90W is safe I think. 65W would be maybe a bad idea if you weren't being super careful. Like if you max that amp out and play it for a few hours at a time I'm not sure a 65W speaker would survive too long.

    Just in case you didn't know all that already.

    Again, really nice work. Is it too bright? :)
     
    itsGiusto likes this.
  20. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    652
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    Thanks!

    I was considering the weber Ceramic 1265, but WGS is cheaper.

    The EV12L is the other big Dumble-style speaker, right? I'm uncertain if WGS or Weber has a take on that speaker.
    Edit: I think it's the Weber Michigan
    But I'm not too clear on the differences between G12-65s and EV12Ls, and which I'd like better.

    I wouldn't say it's too bright (though I did put in a 47pf cap instead of a 68pf for the bright cap). I think it sounds a little brighter than I picture a dumble in my mind, but that's part of the reason why I want to try a more Dumbly speaker.
     
    Last edited: Jan 20, 2021
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.