Help Needed with Tweed Deluxe 5E3 Build

Discussion in 'The Squawk Box' started by Cjsinla, Jul 11, 2017.

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  1. Cjsinla

    Cjsinla Premium Member

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    I built the Tube Depot 5E3 Deluxe kit, it works fine but I think it's not quite right. The volume controls seem to have an effect on each other even when not jumpered. Also, volume drops off between 10 and 12. So, I decided to buy an assembled PTP eyelet board from Mojotone. My plan is to take out the PCB and drop the PTP Mojotone board into the Tube Depot chassis.

    But, when I compared the wiring diagrams from Mojotone and Weber I saw at least one difference in regards to the way that the power tubes are wired up. Tube Depot takes a lead to both #1 terminals and connect a resistor from the #1 and #4 terminals of each 6V6 socket. Weber and Mojotone seem to link the #4 terminals and ignore the #1 terminals and omit the resistor.

    My best guess is that I need to take the resistor off of the socket and take the lead from the board to the #4 terminals when I drop in the Mojotone board. I'm hoping that will not be a problem. And I'm assuming that the #1 terminals end up empty.

    Can anyone tell me why Tube Depot put those resistors there and why other builders did not?
     
  2. Splattle101

    Splattle101 V.I.P. Member

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    The volumes should interact, even without a jump lead. It's one of the 'design faults' of the 5E3. So that's ok.

    Regarding the resistor on the valve base etc. The 6V6 has nothing connected to pin 1. It's a spare (so is pin 6). Pin 4 is the screen. A modern design would put a 1000 Ohm resistor before the screen on each valve. This helps extend valve life and has little if any effect on the the tone. Components are best anchored at both ends to reduce vibration, and pin 1 is a handy anchor point. So what's happened is that TubeDepot have added screen resistors that aren't in the original 1950s design, and they've used pin 1 to anchor them. It's all good.

    You can either:
    a. keep them, and attach the lead from your power supply to pin 1 instead of pin 4; or
    b. remove them and go straight to pin 4.

    Either is fine, but option a. will help your 6V6s last longer, and b. is more 'traditional'.

    Regarding the volume loss when you turn up, try this:
    1. turn both volumes to zero.
    2. turn tone up half way.
    3. plug into normal channel.
    4. turn up the normal volume and listen. As the volume goes up it should get louder and above 4 it should get more and more distorted. The distortion should max out at 12.
    5. slowly turn up the bright channel volume. The distortion should increase. Somewhere between 3 and 8 the distortion will max, and above that point it will go DOWN. As you get the bright volume up towards 10 the volume will drop quite a bit and, by the time you have both volumes at 12, the sound will clean up.

    Give that a go and tell us what happens.:fingersx:
     
  3. Cjsinla

    Cjsinla Premium Member

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    That actually did what you said it would. I must have put it together right.

    Can I assume that pins 5 and 6 have a resistor between them for the same reason that 1 and 4 do?

    Also are there any mods I can do to get the tightest bottom end and max headroom? Or what preamp tubes have less gain; 12ax7 or 12at7?
     
  4. Splattle101

    Splattle101 V.I.P. Member

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    Yes, pin 5 is the control grid, which is where the signal goes into the tube. The resistor from pin 6 to pin 5 is called a grid stopper. It's another modern addition.

    The bottom end is going to be messy. It's another of the design features of the 5E3 and it's part of the sound, just like the rectifier sag and the cathode bias compression. However, it can tightened up a little in a number of ways. You could try a harder rectifier than the 5Y3. Harder rectos would include the 5V4 and the 5AR4 (also called GZ34). DO NOT try a 5U4, cuz it will draw too much current and probably cook your power transformer. There are also some drop-in solid state rectos that you can get, too.

    The other rectos will give higher plate voltages and have lower series resistance (zero series resistance in the case of the solid state recto). The higher voltages will give you a little more clean headroom, and the lower series resistance will reduce the sag which will help tighten up the bass.

    The second way you could tighten the bass is by replacing the coupling capacitors with smaller ones. Smaller coupling capacitors reduce bass, and this tightens up the bottom end. This might seem counter intuitive, but a big part of the problem with flabby bass is too much bass for the power amp to reproduce. So reduce the bass, and it magically tightens up. However, this changes the voicing of the amp. It's no longer a 5E3.

    I wouldn't recommend the 12AT7 as a preamp tube. A better bet for lower gain is the 12AY7 (u = 44), so it's got half the gain of the 12AX7 (u = 100). Electroharmonix makes a 12AY7, and I think JJ make one now, too. Another option is the 5751, which is more like a 12AX7 in sound, but it has lower gain (u = 70), and has lower noise and microphonics. I believe Groove Tube offers a 5751, but I suspect is just a 12AX7 that doesn't meet its gain spec. Vintage ones can still be had reasonably priced.
     
  5. Cjsinla

    Cjsinla Premium Member

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    It has a GZ34 and two 12ax7's in it now, came in the kit. I might try some 12ay7's later. I'm using the amp in the living room. I love the clean sounds and it destroys the Vox AC4 amp I used before. I will never gig with it as it's not loud enough but it's already so loud that the neighbors hear it and my girlfriend complains when I turn it up. I probably don't really need more headroom. I gig with JCM800's when I play out.

    Thanks for all your help but I have one more question. Can I expect better or different performance with the Mojotone PTP vs the Tube Depot PCB? At this point I'm just playing around with the amp as a hobby and I was kinda into the idea that vintage PTP style amps are better with nothing to base it on.
     
  6. Splattle101

    Splattle101 V.I.P. Member

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    I don't think it will perform better. It might be better if it had better components, capacitors in particular. It looks like the Mojo 5E3 board comes with Sprague orange drops, which are the right general type of capacitor (polypropylene film caps), but they're not considered the best for tweed Fenders. Mallory (Dublier) or Mojo's own Dijon caps would be better. But even if it came with super awesome Zoso caps rolled on the night of the new moon and then washed in the tears of virgin unicorns, the difference would be minimal, unless TubeDepot have significantly changed the circuit.

    The biggest difference is that the Mojo board will be easier to work on, if you decide to experiment with different cap values or any other mods. You're likely to damage the traces on the PCB unless you're skilled with the iron.
     
  7. lung plunger

    lung plunger Senior Member

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    Just curious, what did you think about building the tubedepot kit altogether? How long did it take? I've been considering a kit myself.
     
  8. Cjsinla

    Cjsinla Premium Member

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    IMG_1207.JPG IMG_1222.JPG

    I can't remember exactly but it was pretty straightforward and the step-by-step instructions were almost idiot-proof. There is one step were you have to solder in a little jumper setup at position "G" that is used to tighten up the bottom end, you have to solder it in carefully or all three terminals get covered in solder and defeat the purpose for it being there. But, the amp still works no matter how it is soldered.

    I think I spent 3 or 4 evenings on it, my first build. A few hours to solder up the board and leads and attach the transformers , another session to solder the jacks and pots. The hardest part is wiring the tube sockets as the space is tight.

    Also, there are two red leads that get attached to the bottom left of the PCB where the "i" is, and I did not solder them to the board until the board was mounted and a bunch of the other leads were already attached to pots, etc. That makes no sense as the soldering is all done from the bottom. One wire comes from the standby switch and the other wire goes to the output transformer. Try to solder them to the PCB first before you mount it or solder the leads to pots and sockets.

    Other than that, it was a fun project and the amp sounds great. I even bought a Fender logo from Fender for the front.
     
    Last edited: Jul 12, 2017
  9. Cjsinla

    Cjsinla Premium Member

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    @Splattle101

    From the pics I've seen it looks like the eyelet board comes with another piece of fiber board to cover the back and both pieces are screwed down with a couple of screws. There seems to be no spacers underneath. Are the screws sheet metal screws or machine screws with nuts and lockwashers on the back?
     
  10. Splattle101

    Splattle101 V.I.P. Member

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    I don't know how it was done traditionally, and I've never used the fibre eyelet board. I use turret boards with spacers, and these always have machine screws.
     
  11. sonar

    sonar Senior Member

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    The originals used sheet metal screws.

    I've done both eyelet and tag boards in my builds. For one off building I have no real preference. For repair I'd probably prefer eyelet boards.
     
  12. Cjsinla

    Cjsinla Premium Member

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    So I just drill a hole through the two boards and into the chassis and screw it down? From pics I've been looking at, it looks like they may have only used two screws - one on the top left and one on the bottom right. Is that enough?
     
  13. ARandall

    ARandall Senior Member

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    As other have said, the amp seems to be working well and what you experiencing is just the 'features of the amp'
    A 12ay7 is really part of the tweed deluxe experience in V1.
    And others have said the coupling caps (the .1uf ones) are a major source of farty bass. People often go for .047 or even .022. There are several coupling caps that can be switched, but most sites recommend just switching the ones near the 1st gain stage initially.
    This is a good reference with all the parts on the schematic named:
    https://robrobinette.com/How_The_5E3_Deluxe_Works.htm
     
    Last edited: Jul 12, 2017
  14. NotScott

    NotScott Premium Member

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    This!
     
  15. Cjsinla

    Cjsinla Premium Member

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    So, The coupling capacitors are the two capacitors that are closest to where the wire from the number one pin connects to the circuit board? They are marked with a .1 UF on my wiring diagram. That would be C1 and C2 on the tube depot wiring diagram, right?
     
  16. Cjsinla

    Cjsinla Premium Member

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    Got it. Just ordered a couple different ones to try.
     
  17. Cjsinla

    Cjsinla Premium Member

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  18. sonar

    sonar Senior Member

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    Yes.
     
  19. Splattle101

    Splattle101 V.I.P. Member

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    Coupling capacitors connect gain stages. They filter out the high voltage DC part of the signal and just leave the amplified AC signal part. The size of the cap affects the EQ: the smaller the cap, the less bass.

    There are two sets of coupling caps in the 5E3. The first set connects the preamp to the volume / tone network. There are two of them, one for each channel. This means you can change one and leave the other stock, which is a nice way of experimenting. (There is also a single cap between the cathodyne PI and the preceding gain stage, but we'll ignore that one for the moment).

    The second pair of coupling caps connects the PI to the power tubes. You should change these as a pair.

    On my 5E3 I changed the coupling cap for the preamp of the bright channel. I exchanged the stock 0.01 uF cap for a 0.0047 uF. I calculated that with a 1 MOhm pot for the volume, this would give a high pass frequency of 34 Hz, which would be low enough to pass the half frequency harmonic of my lowest note when I tune slack. I left the normal channel stock.

    I like the result. It tightens up the bass of the bright channel without completely corrupting the sound of the amp.
     
  20. Splattle101

    Splattle101 V.I.P. Member

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    Another mod that helps tidy up the sound is to add large grid stoppers to the gain stage after the vol / tone network, and to the cathodyne PI itself. Try doing one at a time to see which makes the most improvement.

    A 1 Meg resistor connected directly to the grid of the gain stage after the volume controls will stop blocking distortion in that triode when you've got the volume maxed. Similar story for the cathodyne. A 1 Meg stopper there will stop the preceding coupling cap acting as a source of charge to flow on the grid of the PI when you've got the volume up. Blocking distortion banished.

    These changes don't affect the voice of the amp at all, but they do eliminate quite a bit of the blatting, flubbing and farting at high vol.
     

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