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And so it begins... Tiny Terror Clone Build.

Discussion in 'Shock Brother's DIY Amps' started by awasson, Sep 29, 2017.

  1. awasson

    awasson Poster Extraordinaire Silver Supporter

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    Well, I’ve been scheming up ideas for a nice compact rig to take with me to jam sessions or even for playing out and I’ve settled on something in the under 20watt range. A buddy of mine uses a Fender Pro Junior for rehearsals and says it’s all he needs so I was considering building a Pro Junior clone when I came across the Orange Tiny Terror.

    This will be my first fully scratch built tube amp. My dad’s been building tube amplifiers since he was about 14years old (he’s 83 now) but I’ve always been a solid state guy. I’ve assisted him in set-ups and troubleshooting and I’ve repaired some tube amps but this will be the first start to finish build for me. It will be point-2-point.

    So I cobbled together some specs and schematics from the web, made up a parts list and sometime around midnight or 1am Tuesday night / Wednesday morning I had my orders in. Hammond transformers (Plus a choke) from Mouser, resistors & caps, plus switches & pots from Digikey. Everything arrived Thursday afternoon.

    363D2E8D-ECAF-4C0F-A569-211A17765C20.jpeg


    I couldn’t find the exact dimension chassis so I got a slightly larger one at: 12” x 8” (bag of fresh components to the right of chassis).

    E355848F-0037-4F7B-9724-0A7E44FBC190.jpeg


    First on the order of business, I’ll lay out the big parts and get the chassis punches and drill bits out. I’m going to come up with my layout, similar to the real McCoy and once I’ve got it all drilled and punched, I’ll paint the chassis white like the original.

    D3EAFB0C-71C7-46D7-9983-986CA8A283B4.jpeg

    I’ll post back once I’ve made some progress.
     
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  2. jasonvilla

    jasonvilla Tele-Meister

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    Nice! I think thats the same size chassis I had. I wish it had been bigger haha
     
  3. telemnemonics

    telemnemonics Telefied Ad Free Member

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    You're adding a choke?
    Good thing you couldn't find the "correct" size chassis!
    Would have needed a second story!
    Bigger OT too?
    Are you putting the OT right over the input?
    Or is this a back view and the choke is over the input?
     
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  4. awasson

    awasson Poster Extraordinaire Silver Supporter

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    Yes, there’s not a lot of room for the transformers and choke, even with the wider chassis. I’m not sure exactly how I want to lay it out. It looks like the real Tiny Terror has the power over the input and then when upgraded with a Mercury Magnetics kit, they put the chokes over on the output transformer side. I may build it without the choke, get it up and running and then add the choke.
     
  5. telemnemonics

    telemnemonics Telefied Ad Free Member

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    The TT has the OT over the input, and the PT over the switches.
    If the PT was over the input it would probably add noise?
    That's a pretty huge choke for a small amp, but I'd think you could squeeze it in by the PT, even if you had toe mount it at a slight angle.
    Wouldn't want to have to move transformers around later, but OTOH the TT and my OR15 sound pretty darn good without chokes.

    I went to put a new 12" speaker in my 6L6 Princeton, and had to move the OT over on the chassis to clear the speaker magnet, so now it sits a an angle.
     
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  6. awasson

    awasson Poster Extraordinaire Silver Supporter

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    Ok, initially I thought that the TT had the input under the OT but thought maybe I was wrong about that.

    So yes, I'm planning on following the original layout for the transformers and controls. I don't think I can add anything to improve on the original design as far as usability goes. I'm leaning towards moving the Power transformer to the rear of the chassis. I'll put the choke towards the front as depicted in this photo.

    IMG_3610.jpg

    EDIT: This might be abetter layout with the PT aligned 90 degrees with the OT

    IMG_3611.jpg

    For 12AX7's I have about 2 dozen to choose from. I've got Marshall, Mesa Boogie, Gold Aero, Sovtek, Electro Harmonix & Ruby.

    I don't have any EL84's yet so the pair of 12AX7's in the power tube position are just for illustration. It just figures that I have several match sets of EL34, 6L6GC and 6V6 pair and only a single EL84. I'm not sure what brand EL84 I should get: JJ, Groove Tube, Mullard, GE, Svetlana... I literally don't have any idea so if anyone has a recommendation, I'm in.
     
  7. awasson

    awasson Poster Extraordinaire Silver Supporter

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    Just a quick update. I finally settled on the layout and spent an afternoon drilling holes. I actually used a 7/8" step drill for the tube sockets and my 1/2" step-drill for everything else.

    IMG_3613.jpg

    I've just mounted everything to see how it's going to look and the tubes are only there for appearances. I still have to get a set of EL84's.

    The only part I need aside from the EL84's is the jewelled power lamp that will be mounted next to the switches. I've got everything else ready to go.

    Next steps:
    I have to cut out the rectangular opening for the power plug in the rear, then everything comes off and I'm going to primer and paint the chassis white. I'll see if I can replicate the decaling and clear coat it. Once the paint is dry, I'll reassemble it and begin wiring it up.

    I'll post again once I've got more to show.

    Andrew
     
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  8. Commodore 64

    Commodore 64 Friend of Leo's

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    That's a monster OT, I believe aimed at Hi Fi users given it's frequency response. That will certainly push all frequencies for ya, I would think bass response is gonna be huge. It also has UL taps, you could make it switchable, UL and traditional. Make sure you use a speaker that can stay together.

    Another consideration with that huge OT, the coupling caps, especially the first one in a TT being 0.001uF -- You might want to make it switchable to something larger, just to take advantage of all that beautiful iron.

    That also seems like a ginormous choke, too 10H 125mA. Are you choking the whole amp or just power tube screens and pre?
     
    Last edited: Oct 3, 2017
  9. awasson

    awasson Poster Extraordinaire Silver Supporter

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    Yes, that's a massive choke. It might be overkill. I was planning on just choking the power tube screens and preamp but if it's within the 125ma power handling, I'll choke the whole thing. I'm not sure about that just yet.

    I had to chuckle at the thought that the 1650E as a big output transformer. You're right, that's actually a decent sized transformer for a 15 watt amp but I'm just used to the ridiculously large and heavy ones in my dad's vintage tube amps. His motto has always been, get a massive amplifier and you'll have all the headroom you'll need. My motto is get the lightest rig you can get your hands on and spare yourself lugging it around. The upside is that I have a really good resource for brainstorming tube amps with and I see him for lunch every Tuesday.

    So yeah... That transformer has UL taps on it. I was thinking of putting a pair of 100 ohm resistors on the screen grids and a switch to put it in/out of UL mode. I was also thinking about adding negative feedback into the circuit on another switch but I want to see how it performs before I do that. Definitely switchable UL mode is a must but I'm not sure about adding global feedback. I've got a pair of 50w HiFi mono blocks, courtesy of dad and they've got global feedback on a switch. I prefer them without the global feedback; they sound more open and lively without it.

    Anyway, I've also made some decisions regarding the cosmetics. I pulled the protective film off the chassis to get it ready for paint but it looks so darn good, I'm going to clear it and keep the shiny aluminum look. I'll do the decaling in black and clear over the whole thing. It'll look something like these photos. Oh, I also scored a great vintage jewelled indicator lamp from my dad at lunch time today. He had a few and this one caught my eye. It's slightly amber glass.

    Anyway, stay tuned more to come as I get going.

    IMG_3614.jpg


    Rear view:
    IMG_3615.jpg
     
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  10. Commodore 64

    Commodore 64 Friend of Leo's

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    I prefer UL with no feedback, too. I've got UL OTs in 2 amps these days, neither have NFB.
     
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  11. awasson

    awasson Poster Extraordinaire Silver Supporter

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    Hey @Commodore 64, Do you mind weighing in on a question regarding the dual gang pots that are being used in this amp for the Volume & Gain controls?

    The schematic shows dual 100K A volume potentiometer with what looks to me like pin 3 of one pot tied to pin 1 of the other and grounded. Does that appear to be correct to you?

    IMG_3628.jpg


    The schematic here shows the Gain dual control 500K A potentiometer with what appears to be pins 1 on both pots grounded. Am I reading that correctly?

    IMG_3629.jpg


    Here's a beauty shot of construction so far. My power supply is wired up, output transformer is wired up. Bridge rectifier feeds A - D with filter caps at each point and a 10 Henry choke between points A & B in place of a 150 ohm 5 Watt resistor (from the original drawing).

    IMG_3627.jpg
     
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  12. BluesBlooded

    BluesBlooded Friend of Leo's

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    Andrew, this is a great project and you have your father to talk things over. It makes for great conversations.

    I think you are right to keep the chassis with a clear coat. It will look great.
     
  13. awasson

    awasson Poster Extraordinaire Silver Supporter

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    Thanks André,

    Yeah my dad is pretty excited to be the wealth of knowledge on tube amps and now that I'm building my own he couldn't be happier. He would often discuss the details of his amp circuitry with me but I could only follow so much. The only way to really get it is to cut loose and build something myself.

    I was thinking about your amplifier build when I was considering clear coating the aluminium. I thought yours looked really sharp with just the lacquer and decals.

    I've got a couple more photos to share...

    • Power supply is wired
    • V3 & V4 Outputs are wired (I still need to wire the DPDT switch for the Ultra Linear taps)
    • Phase inverter V2 wired
    All that is left to do is wire up the 12AX7 at V1, wire that to my input jack and test everything. I've periodically been testing the high power supply at the various nodes and although it is high due to the circuit not being complete, it looks like it is in the right ball park and nothing gets hot or smokes (yet).

    The Power Supply! I used a full wave bridge rectifier on the power transformer, connected to the 1st filter cap 100uF with a 2W - 220K bleeder resistor (2 1W 470k parallel). My ground rail is 12 gauge copper. I would have liked to just have it on one side but I couldn't think of how I could get the P-to-P wiring to it from all of the locations... Hopefully I don't have a noisy amp as a result.

    IMG_3637.jpg


    Another shot from the other side V2 on the top left is all wired up. V1 on the top right just has heaters wired.

    IMG_3635.jpg


    Hopefully I'll have another night or two free to finish wiring V1.

    Cheers,
    Andrew
     
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  14. BluesBlooded

    BluesBlooded Friend of Leo's

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    Remember to give the lacquer plenty of time to cure before you manipulate the chassis.
     
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  15. Finck

    Finck Tele-Afflicted

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    When I had a TT amp some years ago I tried a non matching pair of JJ EL84. Not a single issue with tone (a little more distortion, but that's the deal with the TT) and/or general behaviour. So, I guess you can save some bucks...

    About the larger OT and coupling caps: very probably you'll have more punch even without enlarge the caps. Other side, larger caps can produce a muddy tone.

    The original TT has no issues with hum without a choke, due to huge caps of PSU. But you have already bought the choke, so, it doesn't matter...
     
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  16. awasson

    awasson Poster Extraordinaire Silver Supporter

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    Thanks for the tip on the EL84’s. I was going to buy some unmatched tubes for less that $5 each but decided that since everything else is top notch, I had better get a nice matched pair. I’ve got a set of JJ’s coming and should have them by The weekend. I’ll keep you posted of how it all comes together.
     
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  17. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Unmatched power tubes = more yummy 2nd order harmonic distortion for a thicker clean tone. Matched are for Hi-Fi guys.
     
  18. awasson

    awasson Poster Extraordinaire Silver Supporter

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    Any thoughts about tube manufacturers? I'm pretty sure these are biased kind of hot so I'm not sure all tubes are going to be happy in that environment... Some guys are recommending changing the 120 ohm resistor that ties the cathodes to ground to a larger value like 180 ohms. I'm also planning on switching the UL taps into the circuit via a pull pot on the tone control because I want to be able to run it in a more refined mode as well.
     
  19. robrob

    robrob Poster Extraordinaire Ad Free Member

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    I'm a fan of JJ and Tung-Sol.
     
  20. FenderLover

    FenderLover Poster Extraordinaire

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    Awasson - where did you get the schematic in post 11? The two schematics that I have show the dual Gain and Volume pots are both 500KA. Post 11 shows dual 100KA for the Volume. That's quite a load on the plates of the PI output. It could load down the amplitude excessively and change the response of the amp, so keep that in mind when you start to power up and listen.

    And to answer your question on post 11, terminal 1 of each section of each pot goes to ground. The top schematic was drawn with "knowledge assumed".
     
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