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It begins ... but what is it?

Discussion in 'Shock Brother's DIY Amps' started by goonie, Jul 7, 2020.

  1. dougsta

    dougsta Tele-Meister

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    If it's your 1st rodeo I can highly recommend a good read through the build instructions for the StewMac range of kits, you'll get a good view of what's required for a build, safety, step by step guide and trouble shooting too, you don't have to use the same parts/designs etc.
    You have 2 x ECC83 pre amp and 2 x EL84 power valves and diode rectification, the power transformer might be able to power another pre amp valve but this will be a limiting factor.The EL84 can be thought of as the 9 pin/noval socket version of the octal 6v6.
    Below is a link to the 66 deluxe reverb one they offer, it uses 6v6 power valves and 12ax7 preamp valves. Skip the reverb parts. You can use your EL84s, basically the 9 pin/noval socket version of the octal 6v6.

    https://www.stewmac.com/freeinfo/i-10737/i-10737.pdf

    Here's the PR one too

    https://www.stewmac.com/freeinfo/i-10734/i-10734-F6-screen.pdf

    Doug.
     
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  2. goonie

    goonie Friend of Leo's

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    Update: Still suffering analysis paralysis. Or to be more charitable, weighing up the options carefully before making a decision. Anyway it's all good fun doing the research and learning more as I go.

    Reading up on self-split amps, I've noted a few concerns with 'plate ripple' which is a characteristic of the self-split design. Example below
    https://audiokarma.org/forums/index...one-a-self-split-push-pull-guitar-amp.729948/

    So for my first build, I thought it's not wise to take on a build that might need tweaking to make it work.

    So then I went back to the idea of doing a handwired Pro Junior -- what could be more appropriate as that's what the badge says?
    But there are many negative comments online about the design of the Pro Jr, mainly its tendency to hum ( I can attest to that) and the design compromises made to accommodate the puny OT. An example...
    https://el34world.com/Forum/index.php?topic=9921.0
    "The PJ is just not the greatest of amp designs out there because it is a low production cost mass produced amp that uses extra components to tame the production limitations. The OT for example is tiny and poor quality and needs the extra CF filter to makes it sound less harsh. A VOX AC15, Matchless Spitfire or an 18Watt LiteIIb all sound a world away using less components."

    So it looks to me like the OT has to go.
    I checked out the Matchless Spitfire schematic and it does look fairly simple, plus I'm a big fan of Voxy tones. Tubestore.com has the schematic and layout:
    https://www.thetubestore.com/lib/thetubestore/schematics/Matchless/Matchless-Spitfire-Schematic.pdf

    Of course I would have to modify the circuit a little .. no MV, one input, SS rectifier. And there are some question marks:
    Can I build it in the Pro Jr chassis? I assume so as the tube complement is the same and it has fewer components.
    Is the Pro Jr PT up to the job? It looks like the Spitfire PT puts out 280V whereas the Pro Jr's is 260V
    Is the little 10" Fender-branded speaker up to the job?
    Should I be attempting it as a first build? Maybe a simple Valve Jr/P1 style makes more sense.
     
  3. awasson

    awasson Poster Extraordinaire Silver Supporter

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    I would suggest the matchless spitfire instead of a Pro Jr.

    The schematic looks a lot like the Orange Tiny Terror which I am quite familiar with. I would put a simple effects loop loop between V1 and V2 right after the .01 capacitor. That way you can add some delay and/or reverb without it getting bent out of shape by V1. I did that to the Tiny Terror I built a few years ago and it made the amp so much more useful.
     
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  4. awasson

    awasson Poster Extraordinaire Silver Supporter

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    Well... That’s some compelling stuff. Those Carl’s customs look fantastic and it sounds even better than it looks in the demo they have.

    CORRECTION: It was the Hunt Amplification hand wired Pro Jr that looks fantastic.

    The CJ 11 is also a really nice example too. Again, like the Matchless Spitfire, it’s a pretty basic amp design. Adding the Negative Feedback Loop and making the change to the cathode resistor on V1B are good mods. Again, I’d add an effects loop for Chorus, Reverb, Delay. I like the Tone stack and Volume and Main Volume.

    So many cool designs and so little time!
     
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  5. goonie

    goonie Friend of Leo's

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    My god that CJ11 clone sounds like heaven. But it's got 6v6 power tubes so I wouldn't be able to use the Pro Jr's PT.

    Funny you should link to Carl's Custom Amps @printer2. I messaged him a few weeks ago wondering if he would mod a chassis for me and post it back to Australia! Got no reply so I took that as a sign to do it myself.
     
  6. Jlwctn

    Jlwctn Tele-Meister

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    You should buy that simply as a matter of course, because you aren't going to lose money on it, and it will be more expensive to purchase in the future.
    There is a thread from 2017 on EL34 World with schematics and layouts:
    https://el34world.com/Forum/index.php?topic=21975.0
     
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  7. printer2

    printer2 Poster Extraordinaire

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    No kidding so many cool designs, that is the difficult part. So much for doing a simple amp it seams. If you are going one volume and tone, might want to look at Marshall, you just have a little more power.



    [​IMG]

    [​IMG]




    https://el34world.com/Forum/index.php?topic=21664.0
     
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  8. goonie

    goonie Friend of Leo's

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    Still procrastinating but there's light at the end of the tunnel! Down to a 'final 3'.
    Option 1 is a 5F2a because it's (a) a classic Fender amp, (b) has 2 knobs just like a Pro Jr and (c) is a good starting point for a first timer. BUT I would potentially have to buy a lot of parts, and here in Australia things like PTs and OTs are very expensive (eg Hammond 291AEX $200!). Would it be feasible to keep the stock PT with 260V primary and solid state rectifier?
     
    Last edited: Aug 8, 2020
  9. goonie

    goonie Friend of Leo's

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    Option 2 is hand wiring a Pro Junior using a board and other info from Hoffman
    https://el34world.com/Hoffman/Pro_Junior_Build.htm

    This is of course very appealing as it would keep the amp 'original' in a sense, but it is quite a challenge for a first build. Also there isn't much info around on hand-wired Pro Jr builds, so if I have problems I wouldn't be able to tap into the huge knowledge base that exists for options 1 and 3.
     
  10. goonie

    goonie Friend of Leo's

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  11. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Sure you could. The 6V6 does not tax the PT as much as EL84. The heater draw is half of the EL84.

    Your sonic Heaven waits...

    Take option #4:D
     
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  12. goonie

    goonie Friend of Leo's

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    As someone whose previous wiring experience has only involved pickups, switches and pots, I think discretion will be the better part of valour for my first foray into tubes and voltages. So it's simple and single-ended that wins this drawn-out battle!

    I've been operating under the assumption that if I do a single-ended build using the Pro Jr PT, it would have to be a Valve Jr style amp with an EL84. But if I'm reading things correctly the PT is fine for an 5f2a with solid state rectifier, which would put about 350v into the plate. Sure it won't be a classic 5f2a but if all goes well I'll end up with a cool little amp for the price of a 6V6 and a good quality OT. And with a build under my belt I can be more ambitious next time.
     
  13. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Or... you can use a EZ80 rectifier. It uses 6.3V heater. 9 pin socket. (Marshall used this type rectifier.) You do not need a separate heater tap.

    Your choice of 6V6 or el84 for the power tube. You have the heater current to use either one. even with the rectifier.

    Cool little 5F2A variant. Very nice. Well within your skills. I am sure.

    :cool::cool::cool:
     
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  14. bcorig

    bcorig Friend of Leo's Silver Supporter

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    You mean a BRE 510, correct?
     
  15. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Brock wasn't the only one running the 510, but a BRE 510 would fit the example nicely!

    Still wish riverside kept the raceway. Progress... they say.
     
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  16. bcorig

    bcorig Friend of Leo's Silver Supporter

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    I used to Tech Inspect for SCCA back East Bridgehampton, the Glen, Lime Rock (once). Came to LA in ‘73. Made a bee line to RIR for the Can Am F5000 IROC. Great place to watch a race. Went back in ‘74. After that Life happened. Cancelled Autoweek in 1980...Great times though.
    Those 510s were a sight to see, beating the Alfas and Beemers. Remember Bob Sharp?
     
  17. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Never met him. I watched those races.

    Later, I got into slalom racing with my MGA. Never made the switch to vintage fender to fender racing, been on the track several times though. Never seemed to have enough money.
     
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  18. goonie

    goonie Friend of Leo's

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    Thank you. I hope you're right!

    I have some homework to do so that I understand more about PT current etc
     
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