5E3 with vibrochamp tremolo... help !!!

Discussion in 'Shock Brother's DIY Amps' started by stinga11, Jun 26, 2018.

  1. stinga11

    stinga11 TDPRI Member

    Age:
    32
    Posts:
    48
    Joined:
    Apr 14, 2018
    Location:
    Puerto Rico
    Greetings friends, I am preparing for my next project (This thing about vintage amplifiers is extremely addictive.). I'm still not sure what my next adventure will be but I think I'm going to choose a 5E3 with most of Howard Dumble's modifications. But I would like to add the vibrochamp tremolo but I still do not know where to put it. The schematic is not yet complete but already with what I have done I believe that you can give me a hand. Thanks in advance.
    new??.png
     
    Last edited: Jun 27, 2018
  2. printer2

    printer2 Poster Extraordinaire

    Posts:
    6,314
    Joined:
    May 24, 2010
    Location:
    Canada
    Looks good, wonder why we have not seen much of it done before. I like the whole concept of the amp, I think I drew up something of the sort preamp wise (although I might be inclined to put in a NFB switch).
     
    stinga11 likes this.
  3. stinga11

    stinga11 TDPRI Member

    Age:
    32
    Posts:
    48
    Joined:
    Apr 14, 2018
    Location:
    Puerto Rico
    Thanks for always answering. I already added the NFB switch and I also added the reverb circuit although I do not know if at the end I will leave it. I need help to inject the tremolo signal. I do not know where to inject it.
     
  4. printer2

    printer2 Poster Extraordinaire

    Posts:
    6,314
    Joined:
    May 24, 2010
    Location:
    Canada
    I don't always answer. Some times I get tied up building. Same place the cathode on the second stage, no different than the Champ. Where the heck did the reverb come from? The reverb like that may be a problem. You loose a lot of gain with that 3.3M. I would try throwing it into the Cathodyne stage. First get rid of the 3.3M and capacitor going to the Cathodyne plate. If that was meant to be a grid stopper I would not bother going over 1M, the higher resistances the more noise. There is more to that story but I just came up for air after cutting some wood (should have worn a dust mask) but I need to sand it smooth. You should have enough signal level to put it there, move the 1M bias so it goes directly to the grid, use a pair of 470k resistors as a mixer at that stage and feed the reverb into one and the second stage to the other. Put the vibrato in the cathode, use the same resistor and capacitors as the Champ.
     
    stinga11 likes this.
  5. stinga11

    stinga11 TDPRI Member

    Age:
    32
    Posts:
    48
    Joined:
    Apr 14, 2018
    Location:
    Puerto Rico
    Again Thanks for answering, Let's see if I understood. Would you suggest that I eliminate the Mixer resistor with the capacitor(3.3M & 10pF) so that the signal goes directly to the preamp? The resistance of 1M that you mentioned to me is that of the Dwell potentiometer ???
     
  6. printer2

    printer2 Poster Extraordinaire

    Posts:
    6,314
    Joined:
    May 24, 2010
    Location:
    Canada
    As the schematic in as now you have the input tubes going through two 220k mixing resistors. Say if the lead channel is dialed down to zero and the other channel is cranked, this channel's signal goes through the two 220k resistors and through the other volume control (zero resistance) to ground. The signal voltage is across the two 220k resistors and since they are equal each get half the voltage across the resistors. So that means the middle of them is sending 1/2 the signal to the next stage. But now the signal has to go through the 3.3M resistor before it gets to the next stage.

    The 3.3M (3,300k) resistor is one half of a mixing pair with the 470k resistor from the reverb. So let us say you want the reverb off, the resistance through the reverb pot is zero so you only have the 3,300k and 470k resistors. To find the voltage drop of this pair you have the signal voltage dropped across the 3,300k and the 470k resistor but the signal out is the voltage across the 470k resistor. So we do some math, 470/(3,300 + 470) = 470/3,770 = 12% of our signal. But wait, the signal is already reduced by half from the two preceding mixing resistors. So through them all you actually have 6% of the original signal. Which kind of sucks, but that is what you get when you want to isolate one point from another. Also why the Deluxe Reverb has an extra gain stage to make up for the loss of the mixing resistors.

    Back to the schematic. First the phase inverter triode, you have the signal going to the plate not the grid. You have a 3.3M resistor and 0.02 uF cap, get rid of the cap and change the 3.3 to a 470k. Put another 470k attached to the grid and hook up the reverb pot to this point. I just realized something. You have an extra triode from the reverb recovery tube. It might be more advantageous if you want reverb and trem is to use a Princeton Reverb board and if you want a tweed channel don't put in a tone stack but just a tone control.
     
    stinga11 and Mr Ridesglide like this.
  7. stinga11

    stinga11 TDPRI Member

    Age:
    32
    Posts:
    48
    Joined:
    Apr 14, 2018
    Location:
    Puerto Rico
    Wow, best explanation impossible. I just learned a universe, Thanks. I replaced the capacitor and the mixer resistor with a 470K resistor, add another resistor of 470k to the preamp grid and that point I put the potentiometer of the reverb level. Last question, The 470K resistor and the 0.0033uF capacitor of the Reverb Recovery are removed or I must leave them.
     
    Mr Ridesglide likes this.
  8. mgreene

    mgreene Tele-Holic

    Posts:
    982
    Joined:
    Jan 27, 2010
    Location:
    south carolina
    Hey. Can you point to the webpage where such Dumble Mods can be found? I dont recall ever seeing or hearing about Dumble mods for a 5E3.
     
  9. Mongo Park

    Mongo Park Tele-Holic

    Posts:
    642
    Joined:
    Nov 28, 2010
    Location:
    Winnipeg
    yes I did a search for such things and nada for me...........Ron
     
  10. D'tar

    D'tar Friend of Leo's

    Posts:
    2,133
    Joined:
    Jan 11, 2013
    Location:
    WNY
  11. printer2

    printer2 Poster Extraordinaire

    Posts:
    6,314
    Joined:
    May 24, 2010
    Location:
    Canada
    You need the cap on the recovery plate otherwise the pot would have the dc voltage on it. The 470k on the output of the reverb pot would be the second mixing resistor at the cathodyne grid. If you were to get a pot with a switch for the reverb you could break the signal to the cathodyne grid. This would boost your signal a few dB. The way I look at it I would want reverb when playing cleaner so a couple of dB loss with the mixing resistors is acceptable. When you have the amp cranked up all the way you probably do not want reverb and could switch it out.
     
  12. stinga11

    stinga11 TDPRI Member

    Age:
    32
    Posts:
    48
    Joined:
    Apr 14, 2018
    Location:
    Puerto Rico
    I found two references to Howard Dumble's modifications. The first was on Rob Robinette's website, another user put the link above. and the other reference I found in a Ceriatone model. I leave here the link if you want to see it.
    http://www.ceriatone.com/ceriatone/wp-content/uploads/2018/02/TweedleDee-30May16.jpg
     
  13. mgreene

    mgreene Tele-Holic

    Posts:
    982
    Joined:
    Jan 27, 2010
    Location:
    south carolina
  14. stinga11

    stinga11 TDPRI Member

    Age:
    32
    Posts:
    48
    Joined:
    Apr 14, 2018
    Location:
    Puerto Rico
    I love the idea of having reverb in a 5E3. But I think this is surpassing my knowledge. I made some changes but I'm still not sure if I'm doing what you recommended.
    new??.png

    EDIT:If we add a second stage to each channel before the reverb circuit?
    new2.png
     
    Last edited: Jun 29, 2018
  15. tubeswell

    tubeswell Friend of Leo's

    Posts:
    2,368
    Joined:
    Jul 1, 2008
    Location:
    NZ
    1) You could just inject it the same way they inject it at the cathode of the NFB insertion stage in a vibrochamp; or

    2) Your original design had 4 and 1/2 dual triodes. You could use the spare half to make a virtual earth mixer stage that combines the two input channels with minimal extra gain, and inject the trem at the cathode of that VE mixer (The same way that is injected at the Trem at the cathode of the NFB insertion stage in a vibrochamp)
     
    stinga11 likes this.
  16. stinga11

    stinga11 TDPRI Member

    Age:
    32
    Posts:
    48
    Joined:
    Apr 14, 2018
    Location:
    Puerto Rico
    Thanks for answering!!!
     
  17. stinga11

    stinga11 TDPRI Member

    Age:
    32
    Posts:
    48
    Joined:
    Apr 14, 2018
    Location:
    Puerto Rico
    I already connected the tremolo. Thank you!!!
    5E3New.png
     
  18. printer2

    printer2 Poster Extraordinaire

    Posts:
    6,314
    Joined:
    May 24, 2010
    Location:
    Canada
    Are you saying inject the trem or the verb? I had planned to add reverb to a Champ I built taking the signal after the volume but returning it to the second stage cathode. But as always, too many ideas and not enough time.

    Stinga11, read through my post again about the signal loss with the last arrangement you have with the verb. Even if you don't go for it it would help to see how the options effect the circuit. You can take any stage and plop it into an amp and mix and match but knowing what should happen helps you from going down dead ends. My thoughts were to go into the splitter just before the output stage. But if you have a free triode it might be more advantageous to use it. Must be starting to get crowded in your chassis though.
     
    stinga11 likes this.
  19. stinga11

    stinga11 TDPRI Member

    Age:
    32
    Posts:
    48
    Joined:
    Apr 14, 2018
    Location:
    Puerto Rico
    Greetings, I readed all your post but I am a little confused. I want to learn, to become a guru like all of you. But I get frustrated and I feel ashamed to ask the same thing one and the other time. I made a change in one of the schematic that I posted it above. I changed the resistor of the mixer and eliminated the capacitor but from that point I am a little confused.
     
  20. printer2

    printer2 Poster Extraordinaire

    Posts:
    6,314
    Joined:
    May 24, 2010
    Location:
    Canada
    Most people here didn't now how electronics worked at some point in time. Me, I can't remember back that far, not a guru, I just know enough and have no interest to know what the real smart guys know. You need to know resistors in series and parallel, voltage drops around a circuit (which means Ohm's Law), a few other things on top of that. Google these and download the following.

    http://www.ax84.com/p1/P1_Theory_Document.zip

    On the above schematic, you have a mixer pair of 220k resistors, which is fine. But then you have the 3.3M resistor and the 470k resistor, which act as another pair of mixing resistors but take the output of the first pair and the reverb signal and mix them. The problem with resistors used this way (but we need to isolate the two circuits so we grin and bare it) is they drop the signal. Having two sets in series drops the signal more than desired. The larger resistor drops more of the signal so with the reverb pair we are dropping the main signal more. Rather than that I was thinking drop the main signal less as usually people find they have more than enough reverb and only are able to turn it up to 3.

    So I thought give them roughly an equal resistance. The problem with putting the mixing resistors where you have them at the current position is that you are taking the signal upstream of the dropping resistor. Not normally a problem with a 3.3M resistor but with a resistor much smaller you can accidentally feed back the reverb signal back through the resistors and into the input of the reverb circuit. So I thought take the reverb send from where you have it and then mix the reverb back in but behind the next stage. There is no chance for the reverb signal to feed back into the reverb circuit. Now the problem is that it might take some playing around with values to get a good compromise. For a person well enough versed in amps it might not be a problem, for someone not up to speed it might be asking a little much.
     
    tubeswell likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.