Scrap Scratch build - Definitely need advice

Discussion in 'Shock Brother's DIY Amps' started by rojo412, Aug 1, 2019.

  1. rojo412

    rojo412 TDPRI Member

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    Is there anything I'll be measuring in the DC setting on the multimeter?

    Thanks for the advice, too. Much appreciated.
     
  2. rojo412

    rojo412 TDPRI Member

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    The yellow leads read 5v.
    The green and white read 6.4v.

    Seems like this thing is doing good so far. But what does it mean for this project?
    As a total noob here, I can still guess that this thing is not going to end up in a tiny practice amp situation.

    And how should I be testing the other transformer?
     
    Last edited: Aug 6, 2019
  3. rojo412

    rojo412 TDPRI Member

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    One of two things either just happened: I helped out the learning process of this OR I just added more complications.

    Long story short, I bought this amp from a buddy:

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    It's an EARTH SOUND RESEARCH amp from the 70s. From what I've read, they basically copied Peavey, copying Fender (to some degree), then went out of business before Peavey could sue them.
    It was $80. It has a tube power section, but a solid state front end. That is something I may change if this becomes worth the effort and I hope it is.

    My thought was, it has a lot of parts that could be used if I wanted to gut it and redo it OR it's a template for pieces of this scratch build project OR I use it to learn how to diagnose and fix issues, as well as learn some mods and whatnot.
    I'm not certain this is the area for this and will gladly post elsewhere if this tangent isn't appropriate.

    BUT... if anyone wants to help me on this project, here's the story...
    The amp supposedly worked. But my friend lost the fuse cap when he moved and it's been sitting in his basement for a long time. He's a drummer, what else can I tell ya?
    - Bring it home, put a fuse into it and the wrong kind of cap on the top of the fuse area: Instantly fries the fuse.
    - Realizing that the voltage limiter was built for reasons like this, I plug the amp into that, put in a new fuse and the wrong cap, flip the switch, bulb lights up on the limiter. Turn it off, fuse remains intact.
    - Flipped the ground switch, try again, same result. But when I grab the fuse, I get a mild shock. Just a tickle, no spark or jolt. OOPS!
    - Out of sheer curiosity, I pull the tubes, put the fuse in, turn it on, no bulb limiter light. But I honestly don't think the actual amp power bulb works, so I don't know if anything was working to begin with.

    My first attempt of a minor fix is to replace the fuse socket with the one from the stereo. They mate together well (because they were built to work together) and that seems like a pretty straight forward swap. Plus, it needs a solid fuse holder anyway.

    With those symptoms, what should I be looking at for a fix?
    I can find no real info on this amp. As in, I don't see a thing on this amp, aside from the company name AS WELL AS no real info on the web. The tubes that came in it are 5881s, and I honestly don't know if those are even supposed to be in here. It's kind of a basket case! Be careful what you wish for, eh?
     
  4. bigguy12321

    bigguy12321 Tele-Meister

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    @rojo412 Cool amp. Yes it will be tough to find info on this but I did find this sight (http://earth.ampage.org/) and it seems to be the Revival 112 series amp.

    There was one post on there that indicated a blowing fuse due to the rectifier section. I searched "Revival" and it came up near the top.

    Hope this helps get you started. There is also one for sale on Reverb. Not mine or anyone I know but it's there.

    a
     
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  5. rojo412

    rojo412 TDPRI Member

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    @bigguy12321 You are my hero! Thank you so much for that info, that is the lead that breaks this case wide open.
    Pretty funny, too, that the name is the "Revival" since that's what this so desperately needs.
     
  6. bigguy12321

    bigguy12321 Tele-Meister

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    Easy there @rojo412 .

    I generally fail hard in that hero role...

    If you can't get it going as is, I'm sure there is enough power there to build it with a tube front end. The dirty cab has tons of mojo itself and deserves to be resurrected.

    Have you pulled the chassis out yet? It'd be interesting to see the whole thing. It appears to have excess octal cutouts for some reason. Maybe they used one chassis for all their models. Some had 4 output tubes.

    Glad I could help. Sometimes my google-foo is right on.

    a

    p.s. Stop grabbing live fuses.
     
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  7. rojo412

    rojo412 TDPRI Member

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    Hey, all I can say is, you clued me into the name of the amp and now I can start getting deeper into the search.

    From what little pics and schematics I CAN find on these, it most certainly seems like they used this chassis for other models. The schematic for the beefier Revival has 4 6L6 tubes. And if you turned this into a head, you could re-orient the tubes vertically.

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    And I've been carefully cleaning and steel wooling the face to try and make it more legible, yet not remove the silk screened text.

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    Not perfect, but this thing never will be without some MAJOR surgery.
    And FWIW, the covering is what I'd probably describe as either "Tweed-ex" or "Tol-Weed". It's a vinyl-ish covering, meant to look like tweed, but it totally feels gummy.

    So here's a concern of mine and maybe someone can help me out...
    The amp came with 5881 tubes in it. Looking at those, they have 6 pins on the bottom. But looking at the tube sockets, there are 7 connections hooked to wires. That seems off.
    Also, the other amp schematics for the bigger versions specify 6L6 tubes. So I gotta ask: could that be a clue to these blown fuses?
    Speaking of fuses, I got the 5A fuse pack from Lowes that was $1.72 or something. They aren't slo-blow or anything like that. Would that make a difference?

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    Here's some more pics, if you care to see them or they can help shed light on anything.

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    The text on the reverb tank is pretty awesome:

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    It should also be noted that with the vastly adaptable nature of this chassis, the thought of building the amp from scratch with this as a testing ground would be a serious consideration.
    Certainly, I'd try to utilize a design that fits well into this (not sure which design this copies). It would allow me some options on whether to go with a really basic, low-power design at first, eventually adding more to it as I learn... or just going the whole hog and make this thing breathe fire to begin with. Either way, if I can get it to make noise, I'm happy with my $80 expense.
     
  8. magic smoke

    magic smoke Tele-Meister

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    @rojo412 , Nice find with the drummer’s amp! The most expensive parts for a build are transformers, speaker, cabinet and chassis... and your chassis was designed to hold just about any circuit desired. Look around at some classic 6L6 family amps. (tube or solid state rectification in yours?) You might even be able to find a kit board to build /drop in. This is a great time to enhance knowledge by reading valve amp schematics . Congrats on the new project!
     
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  9. magic smoke

    magic smoke Tele-Meister

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    BTW, slo-blo is the way to go. Keep it plugged into the limiter until you have it running smooth. Sometimes builders utilize otherwise unused pin/socket tabs to hang components or facilitate tube swapping.
     
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  10. rojo412

    rojo412 TDPRI Member

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    I ended up making a separate thread on the topic of this ESR amp, since it was more "service" and not so much "from scratch."
    A lot of the learning process on that has been somewhat difficult since the design is weird to begin with, who knows what others have done to it in the past, and it still doesn't want to work.

    All that said, if it ends up being too much trouble to get that going, I'll likely be removing the guts and using all of the stuff I can from this project to make it into something else.

    SO... Here's what I've established with the Fisher transformers:

    PT -
    It has the sections for 5v and 6.3v that function.
    The red wires produce 840-ish volts, but with no tap wire. That seems like a lot of volts!
    The brown wires produce 431 volts, with the red/yellow wire being the tap and both sides produce roughly half of that.

    OT -
    Doesn't seem to have any shorts. It has resistance on the primary side that makes sense. And it doesn't have connectivity between the two sides, so I think it's okay.

    Where should I be going from here? What type of amp design should I be looking at with transformers like this?

    Also, I just spotted a Craigslist ad for a Hammond amplifier chassis with everything but tubes. Should I be jumping on that or not bother?
     
  11. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    For $30 I’d be on that one. The PT is a great one for guitar amp builds but the OT is likely not .... many of those were driving field coil speakers.
     
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  12. magic smoke

    magic smoke Tele-Meister

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    There is your power transformer for the ESR. That iron should have enough juice to run the 6L6s and a tube preamp section
     
  13. rojo412

    rojo412 TDPRI Member

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    Right on. Perhaps a Fisher/ESR hybrid project is in order...
     
  14. Commodore 64

    Commodore 64 Friend of Leo's

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    Rojo, I'm in NE Ohio too.

    Did you feed the transformer with 120v? That would suggest a 420-0-420 transformer. That's pretty beefy. Prolly would sag some under load. I use a 350-0-350 for pair of 6L6 or EL34.

    If you are serious about starting this hobby, perhaps we could get together sometime, I need to get my shop back in order, but I think I could help accelerate your learning curve and I have things like a power supply we could send 3V to unknown transformers (instead of 120v). And other fun stuff like an oscilloscope to trace signals.
     
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  15. rojo412

    rojo412 TDPRI Member

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    That would be amazing, thank you! I'll send a PM for details.

    I connected it to the voltage limiter to supply power, if that gives it 120v.
     
  16. D'tar

    D'tar Friend of Leo's

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    I would bet with the Commodore by your side... You could have that ESR figured out pretty quick!!!!
     
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  17. jtcnj

    jtcnj Tele-Holic

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    Congrats on a new found obsession, and on the great parts finds.
    Good luck with your projects.
    Having someone experienced to help you along is a real help.

    That said, just my $.02 you are jumping in here where an intermediate level of knowledge would be much more suited to these type of salvage operations. I am largely repeating what I have read as I got started.
    I have a few good running builds but I am no expert.

    If you really want to learn and do this more as DIY than paint-by-numbers assembly from a kit,
    you may want to consider sourcing the parts yourself, and building a common simple circuit.

    A tweed champ or princeton - 5F1 or 5F2a etc. will give you tons of basic tube amp knowledge, if you companion it with basic tube electronics theory widely available.
    There is also lots of support from the many, many here that have built them.
    Especially if something is amiss.

    I'm not saying you shouldn't do it, though.
    If you have hands on help throughout this salvage build you may come away with a nice build.

    The light bulb current limiter is a must have, glad to see you built one.

    Please carefully watch the videos and adopt the safety practices such as this one:

     
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  18. rojo412

    rojo412 TDPRI Member

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    Okay, after messing with the ESR, I changed my mind: I'd like to scrap build something with these transformers, but keep the whole amp as simple as I can. Basically, just volume and power, maybe a standby.
    Is it possible to build a 5w or 15w amp with these things? Or are these too much for that?
     
  19. Buzzgrowl

    Buzzgrowl Tele-Meister

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    Agreed. If you want to play your guitar through it, could it be simpler to buy or build a small transmiter that your restored radio could tune in to?
     
  20. rojo412

    rojo412 TDPRI Member

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    It's already past the point of no return. The Fisher is no more. It has ceased to be.
    :D
     
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