Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups darrenriley.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

NAD!

Discussion in 'Glowing Bottle Tube Amp Forum' started by Asmith, Oct 2, 2018.

  1. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    Just finished this off this morning, its a modified Vox AC15 top boost preamp/tone stack into an el84 single ended power amp.

    WP_20181002_20_29_25_Pro.jpg
    WP_20181002_18_21_32_Pro.jpg
    WP_20181002_20_43_09_Pro.jpg
    WP_20181002_18_21_21_Pro.jpg

    I have a build thread here: http://www.tdpri.com/threads/first-build-and-something-a-bit-different-take-2.873969/

    but here's the details in brief. The original AC15 top boost has 3 triode gain stages in the preamp but 12ax7s are dual triodes so I swapped out the first gain stage for a depletion mosfet (LND150) then followed with a 12ax7 so its like pushing a valve amp with a clean boost.

    The knobs are volume (gain), treble and bass, 2 switches on/off and a tone stack bypass. I'm probably going to add an attenuator and maybe a switch to add more bass/mids to give it more of a Bassman/Marshall tone.

    I'm planning to build an enclosure for the head and I'm hoping to adapt the cab underneath for a bigger speaker (10").
     
  2. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    I'm going to see about uploading a sound clip soon but I'm too eager to get this enclosure built and ill probably upload a second clip with the new cab once that's finished.

    WP_20181005_13_39_13_Pro.jpg
     
    JustABluesGuy likes this.
  3. Silverface

    Silverface Poster Extraordinaire Ad Free Member

    Age:
    66
    Mar 2, 2003
    Lawndale CA
    Nice - I like your open physical design. It makes it easier to work on/mod and solves a ton of potential lead dress hassles by inherently separating high voltage and signal wires.

    Looking at the schematic and supporting datain the other thread it appears you really did your legwork. It's really well thought out - amazingly so for a first or second build. Did you have any electronics background before this? If not it looks to me like you did a darned good job of educating yourself before designing both the electronics and the layout.

    look forward to hearing it.
     
    Piotr and Asmith like this.
  4. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

    Feb 15, 2014
    Maine
    Very cool, a mini classic. I'll bet it soundsawesome.
     
  5. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    Thanks for the high praise! Its my first build but my relevant background is in physics so I understand that high current circuits and transformers produce B fields so it was just about keeping those elements separate from the signal path especially the input and first gain stage. Also twisting send and return leads (which turned out to be anything attached to a transformer) to cancel out B fields.

    I did well for space, the chassis is designed for a 5F1 style build (SS rectification/power supply) with the power switch on the back near the IEC socket and only an indicator light and a single gain knob on the front.

    My only other electronics design experience is with pedals but other than schematic work it usually comes down to cramming as many components as possible onto stripboard without consideration for much else. I probably spent a good solid month designing and researching valve circuits. (valve wizard, @robrob's site and the valve museum we're very helpful.)

    I moved house recently (renting) and had to sell my amp to fund the deposit so I was broke and without an amp so playing guitar wasnt as fun and designing an amp is a free pass time. I figured I could build a replacement valve amp for the same cost as a new amp and also have a platform to build something really special. Originally I was thinking about an ecl86 and a 12ax7 (3 triodes + pentode) but it evolved due to a myriad of obstacles.

    I'm hoping to get back on the work bench on Monday. I should have the enclosure ready to tolex but that'll probably be a while off since buying a new speaker and sorting out the cab are the priorities.
     
  6. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    I managed to find some time today to make this mess,

    WP_20181006_16_46_11_Pro.jpg

    but its shaping up pretty good,

    WP_20181006_16_47_11_Pro.jpg

    I've planed 2 out of 6 sides level, its currently held together with some screws which are counter sunk to allow planing in its current state. Once its all level I'll take out the screws put some glue down on the top panels to form some sort of lid, put it back together, I'll round the corners off and then ill probably think about what colour tolex will look best.
     
    JustABluesGuy likes this.
  7. heltershelton

    heltershelton Tele-Afflicted Silver Supporter

    Sep 14, 2016
    not houston
    that is really cool, but you might think about putting a vent or two on the top.
     
  8. Silverface

    Silverface Poster Extraordinaire Ad Free Member

    Age:
    66
    Mar 2, 2003
    Lawndale CA
    That's a great approach. Kit builders should pay attention to this - in many cases they just do "layout assembly", and a month spent studying tube circuits would make the experience much more educational. And more likely to be trouble-free.
     
  9. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    Yes, I'm looking for a black mesh grill to put over the valve side or failing that I'm sure you can buy vent covers for amps. The back is open too so I can get a convection current. I'm thinking dark green for the tolex if I can find a good supplier. Cream is also a contender.
     
    heltershelton likes this.
  10. heltershelton

    heltershelton Tele-Afflicted Silver Supporter

    Sep 14, 2016
    not houston
    i just had a thought. if you got some black mesh, you could cut a hole, and then around the hole you could route a small maybe 1/8 or so of an inch thick area to a depth of the thickness of the mesh plus the screw to hold it. that way the mesh will be sunk and youll never cut yourself on the sharp edges.
     
  11. heltershelton

    heltershelton Tele-Afflicted Silver Supporter

    Sep 14, 2016
    not houston
  12. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    I definitely felt I learnt a lot more than a kit could provide, I had to understand the data sheets and a lot more theory. What I learnt is why didn't follow through with the elc86 + 12ax7 design because the triode on the elc86 didn't have a very large kf voltage rating so it couldn't be used as the source follower and I didnt like the idea of using it in the preamp and yhe 12ax7 for the source follower because the layout would have got messy. I also couldn't source a suitable OT (16-8-4 ohms to 7.5K ratio) that was rated at 3 watts+. The source follower issue is also why I raised the heater voltage and I don't see why it isn't standard in Vox amps
     
  13. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    I was thinking the same but I'm in the uk so I would be looking at other suppliers if possible. Finding a neater solution would be nice though.
     
    heltershelton likes this.
  14. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    Reading the shock brothers section doesn't seem like a wise thing for me to do, I'm struggling to resist the urge to mod this amp already. I'm happy with the tone but I've always liked a good built in reverb. I know I don't have the space for a good sized pan in the head or cab but I might built a stand alone effect that plugs into the amp and runs externally while leaving it stock disconnected.

    I like the reverb in my friends HRD and have a transformer suitable for a SS reverb that can provide a big enough voltage rail for the signal voltage just before the power valve if it can go there but I'll do the research one I've finished my current tasks to see if its worth while.

    The enclosure is coming along well, I don't know if it showed in the pictures but the pine I used wasn't immaculate. It has holes all over it as I've drilled other pieces with this behind them (like this amp chassis). So its going to get a lot of filler and sanding to cover the imperfections after the planing process. It's going a bit slow at the moment because I'm dealing with the end grain but its nearly there.
     
  15. Paul in Colorado

    Paul in Colorado Telefied Ad Free Member

    Mar 17, 2003
    Fort Collins, CO
    For reverb you might consider a Surfy Bear kit unless you really want to design and build it from scratch.
     
  16. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    I can put something together of equal quality with for a lot less (its £50 without the reverb pan and power supply). I can probably do it for about £30 with my current transformer, I can also stick an FX loop since I'll be back to playing with safe voltages and op amps. I was just going to copy the reverb from a HRD or maybe a blues junior and then alter the gain at the input and recovery to make it suitable for the input voltage and out voltage. I'd just need to get an estimate for the signal voltage at the end of the end of the preamp in known designs. Again @robrob's site has a useful section on this.
     
  17. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    The SS reverb shouldn't alter the tone as much either it will probably just drop the signal voltage into the output valve by about a quarter but I won't want a lot of power valve distortion if I have the reverb/effects loop on.
     
  18. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    I'm thinking about recording a quick demo this week, I got it going loud (halfway up the volume knob to edge of break up) yesterday but not for long to not annoy the neighbours. Otherwise its been clean so I ordered a stereo 8 ohm lpad attenuator (15 watts). I'll use both pads in parallel so that it matches the 4 ohm speaker but I can also use it with an 8 ohm speaker when I upgrade.

    The enclosure is coming along well just prepping it for paint. I was going to tolex it but it would add cost to a cheap build so I'm going to paint it with blackboard paint instead.
     
  19. LudwigvonBirk

    LudwigvonBirk Tele-Holic

    Age:
    117
    614
    Aug 26, 2017
    Madison
    Is there a fuse hiding somewhere? (I didn't see it in your pictures)
     
  20. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    the mains iec socket has a built in fuse, I've put in a 200ma slow blow. I did the maths in my build thread but it should be about right, my current draw on the high voltage was about 65ma and the heaters should be under 1.5A.

    IIRC the amp uses 25 Watts so at 240V that's roughly 100ma valve Wizard or Robs site recommended doubling the fuse value (something similar as it was a range) so I went with 200ma since they're easy enough to find. There's also a 3A heater fuse but its probably never going to be of any use.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.