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Earth Sound Research amp needs some love

Discussion in 'Amp Tech Center' started by rojo412, Aug 8, 2019.

  1. rojo412

    rojo412 TDPRI Member

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    I've just recently started taking an interest in tube amps. I'm making an attempt to build one from scratch using scrap parts and that is going along okay. But I just picked up this amp from a friend on the cheap, in an effort to learn even more and to have something complete to mess with should I need it.

    IMG_5567.JPG
    It's an Earth Sound Research 1x12 with a tube power section and solid state preamp. With the limited amount of info available on these, it's certainly feeling like a steep learning curve.
    My buddy says he had it working, but lost the fuse cap when he moved, so it's been sitting for a while.

    I put a fuse into it and put an ill-fitting cap on the fuse holder, flipped the switch and it blew the fuse immediately.
    Realizing I should probably have this plugged into a voltage limiter, I moved the plug to that and tried again. The bulb on the voltage limiter lit up, but the fuse didn't blow.

    Essentially, this is blowing fuses and not allowing me to power it up.
    If anyone has advice on where I need to begin fixing this, it would be very much appreciated. I do have a better fuse holder which I think would be a good thing to install, as well as a good start to this project. But beyond that, I'm still new at this.

    IMG_5568.JPG IMG_5569.JPG IMG_5570.JPG IMG_5571.JPG IMG_5572.JPG IMG_5573.JPG IMG_5574.JPG IMG_5575.JPG
     
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  2. Wally

    Wally Telefied Ad Free Member

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    Take this with all of the consideration you think it is worth, I put imho that amp is not one with which you want to begin learning about tube amps. For one, it is a hybrid. Secondly, it is not the simplest of amps...fwiw, it is a rough clone of a Peavey design. Thirdly, someone’s has already been working on the amp and has given up. They may have given up because after replacing most but not all of the electrolytics they hit a wall due to lack of experience....or if they had the experience and knowledge and found found the problem they did not want to go to the expense of replacing a major component like the PT???
    If a person had the experience, they could get that going. How much work and expense that would take is unknown. How much the amp is worth is known....in its present condition it is of no worth to me personally other than there is one big Eminence speaker there.
    In working condition, my money still stays in my pocket. Ommv.
    If you read schematics and can find such a document for the amp, then proceed. If you don’t read schematics and/or you cannot trace PCB circuits, then I say you should find a simpler project with which to begin your tube amp work.
     
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  3. Wally

    Wally Telefied Ad Free Member

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    Fwiw, I brought a 4x6L6 Earth all-tube head back to life years ago...no schematic available to me at that time. It was a rough clone of a BF circuit. The resurrection turned out well and the amp is still in operation last I heard. Being all tube and very traceable terminal strip construction, it was something worth the effort. It was not my first effort in amp work, though.
     
  4. D'tar

    D'tar Friend of Leo's

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    Listen to Wally!!! I hear he knows what he is talking about;)! My .02.... Figure out what circuit "you want" that comes close to the control configuration and would be able to use your transformers. Junk everything that can't be re used and build from scratch.
     
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  5. Preacher

    Preacher Friend of Leo's

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    This^^^

    With that chassis and the components you have in there I would gut it and start over. Many of the resistors and capacitors on the main board can be removed and you can create your own turret or eyelet board on the cheap and re-solder those components in there.

    That is the making a nice 5E3 although I can't see what kind of power tubes are there. I am sure there are some others that will chime in with some info.

    here is a little video of its brother.
     
  6. Preacher

    Preacher Friend of Leo's

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  7. rojo412

    rojo412 TDPRI Member

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    The whole beginning of anything here was my desire to learn how to build an amp from scratch. I ended up with an old tube radio I got from my grandparents basement and was starting with that to learn how to test things and reuse them.
    Since I was able to snag this cheap, I figured either I can get it to work as is and then modify it from there... or just gut it and use the chassis, speaker, and cab to build something else.

    I'm definitely with you guys on the fact that this will be tricky. There's no info on these particular ones out there, it's got a weird layout with the SS preamp, and they don't seem to be worth much when they do function. But like I said, I just want to learn and am not afraid to eventually gut this. Just figured I should at least try to make it work and go from there, making the attempt with it is practically free.

    This amp has 5881 tubes in it. And in all honesty, I'm not sure those are even correct. The other Earth diagrams I see have 6L6 tubes in them.

    Here's some closer pics of things if anyone wants to take a whack at more diagnostics.

    IMG_5581.JPG IMG_5582.JPG IMG_5585.JPG IMG_5586.JPG IMG_5587.JPG IMG_5580.JPG

    And let's say that I do gut this thing. The chassis has a ton of room for other components, so I'd probably opt for a project that is more advanced than a Champ because... why would I want a huge, heavy, relatively empty Champ clone with a bunch of empty holes?

    What setup would you recommend for this chassis?
    - Would like to keep the reverb
    - Would be more into something with footswitch clean/dirty capability
    - Don't need anything super high-powered

    Thanks for all the help, too. I very much appreciate it.
     
  8. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    All the things you're mentioning are not beginner-level projects. Multi-channel footswitching is just not something you're going to get an easy breakdown of.

    Aren't you the guy with the couple of radios from the other thread you're playing with? If so, I'd do this:

    -play with those
    -put this in a corner until you're more comfortable with more advanced projects.

    That amp is running 2x6L6, but not sure it that PT has enough juice to start adding some 12ax7s. Codes on the PT might help determine this. That reverb is also solid state, so you'd need a different pan to use in a Fender-style reverb circuit as it will have a different impedance.

    I don't want to be discouraging, but I just don't picture this project ending well as a beginner one, or possibly even intermediate. Gutting the whole thing would likely be more rewarding, or you may even be able to sell it as is to pay for parts.

    Troubleshooting blown fuses? How do you troubleshoot anything? Isolate the issue. Pull the tubes, and disconnect the power transformer secondaries so there is no high voltage connections, which means there is no current on the secondary side anywhere. Still blows? Could be a bad switch or bad transformer. I have a bunch of little circuit breakers connected to clip leads that I use so I don't end up going through fuses like candy.
     
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  9. D'tar

    D'tar Friend of Leo's

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  10. rojo412

    rojo412 TDPRI Member

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    I am that guy, yes. Since this was an aside from that, I thought a separate thread was in order.

    And yeah, I totally get it, what I've mentioned may be a long ways away for me, but I really do enjoy jumping in with both feet on stuff like this.

    If I were to gut this completely and do a different type of circuit, I was just wondering which type of amp design would be the one to look for to accomplish that end result. I personally don't know much about guitar amp models at all. But I really want to know more!

    One thing I wasn't aware of was the fact that a different preamp and reverb tank would change things like you mentioned. So that kind of just puts the immediate goal of this as "Make it work again." Any drastic changes down the line would likely be done in a full gut situation. And of course, there's the logic of "this amp isn't worth that effort." I get that.
    All I'm trying to do is develop a better understanding of the functionality of all of these things.

    That said, the current goal for today is to change out the fuse holder to something that functions and replace the bulb so I can visually see if the amp powers up.
     
  11. Wally

    Wally Telefied Ad Free Member

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    I would take a WAG that one could build a single channel amp based on the Normal Channel of a Bassman 10 circuit and not over stress that PT. This would be a clean amp. Or...one could build a single channel of a 5E5 tweed Pro using the same tube compliment...2 x 12A-7’s and 2 x 6L6’s. This Pro is essentially a 5E3 Deluxe with 6L6’s in the output.
    Take a look at the schematics and see what you think. Hey, if that PT burns down, it is a small loss, imho.
     
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  12. Preacher

    Preacher Friend of Leo's

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    The schematic I posted shows 6L6s at the power stage. That is where I would start after sorting the fuse issue. I would also bring it up to speed with a limiter to make sure you don't do any additional damage till you get that short sorted out.

    Amp building can be satisfying but it is also meticulous even when starting from scratch.
    Here is what I would do.

    Sort out the fuse issue, get some 6L6s in the power side of things and fire it up on a light bulb limiter. If it emits sounds then I would play around with it a little to see if you can dial it in.

    If you do the above and still get no sounds, I would look at a maybe doing a 5E5 tweed pro where you would add the two 12AX7s and you would still get to use the 6L6s so they would not be a loss.

    Check out the trannys to see if they will handle it and go from there.
     
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  13. rojo412

    rojo412 TDPRI Member

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    I do have a voltage limiter. When the amp is plugged into it and turned on, it glows brightly! And it stays that way. So that's not great.
    But yeah, the fuse issue is definitely first and foremost. I'm assuming it's not as simple as having a Slow Blow vs a regular 5A, right?

    What is the difference between 6L6s and 5881s? Would using these 5881s blow fuses?

    Here's the numbers from the transformers:
    IMG_5589.JPG
    IMG_5590.JPG
     
  14. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    It depends, if they are more modern tubes, likely not much difference at all.
     
  15. D'tar

    D'tar Friend of Leo's

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    Without tubes?

    pull the 5881s... still bright?

    pull the rectifier... still bright?
     
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  16. Wally

    Wally Telefied Ad Free Member

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    Transformer codes..... that 668 EIA code is not a familiar to me, and I do not find it in a quick search.
    If the light bulb is at full brightness in the current limiter, then it is confirming what the blown fuse says....there is a short in the circuit. Where is the short??? Who knows? You could pull the tubes and see if another fuse blows. If not, put the tubes back in...does the fuse blow? If so, you have a bad tube, bad OT, blown resistor.....lots of possibilities. It would take some research to understand where the fault is. That research would be a learning process for you. I do not know your experience so cannot advise. Imho, after one did all of the research and if one got the amp going, it would have eaten more time than it is worth. Ommv.
    Good luck with it.
     
  17. Teleguy61

    Teleguy61 Friend of Leo's

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    Please, be safe, be sane.
    From what you are indicating, this amp is over your head.
    Listen to Wally.
     
  18. rojo412

    rojo412 TDPRI Member

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    It doesn't have a rectifier tube, it's just the two 5881s. And it glows very bright with or without them.

    I'm doing my best to read all of the info that's been provided so far. It's daunting, but I really enjoy the challenge. For many years, I've been looking at schematics and not quite grasping the info without some serious focus. But the more I do it, the more it's sinking in.


    Of course this amp is over my head! Aside from a random fix here and there over the years, this is the first time I've delved into one seriously. But my ultimate goal here is to learn about them. I want to know what I'm not doing right and learn to fix that. The reason I'm on here asking questions and seeking guidance is to help gain the experience to do this more often. This is how I've been operating for many years, it's just the way I am.

    There's no doubt in my mind that I need to be careful and meticulous when dealing with this amp or any electrical device. If it helps to qualify my experience with "danger" involved in repairs and crafting, I can tell you that I operate dangerous tools almost every day. An example is my 14" bandsaw that could mow through a limb like it's a toothpick. But to get it that way, I had to learn how to completely rebuild it, learn how to properly wire the motor, learn to set it up right and then learn to use it carefully.
    I do all of my own auto repair and am frequently in danger with that, but I take precautions and seek help to do things the right way. Over years, I've continued to learn and practice it so I don't have to pay someone else to do it.
    I've worked in construction and done home wiring. Yeah, it was scary to learn, but it's not impossible.

    Searching out the issues on this amp may seem kinda silly, but there's a certain satisfaction that I'm seeking in making it work. And if I eventually find that I can't make it work, there's a satisfaction in knowing that I tried.
    The way I see it, this is a cheap way to start. If it's gonna be that bad, I'll find that out, gut it, then build something else with it. There are plenty of websites selling parts, kits, etc which are all brand new and ready to go. I know that's the possible outcome, but certainly like the challenge of making it work up until that moment.
     
  19. Wally

    Wally Telefied Ad Free Member

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    Rojo, a study on the history of vacuum tubes is a good start to understanding those schematics in that the functions of the various elements of the tubes will be explained in a basic way. Then, a site like Duncan Tube Data Sheets will allow you to research any tube to learn the pinouts. Ime, understanding the functions of the elements along with the pinouts gives a person insight as to what goes on in the circuit.
    Do you understand the Power transformer windings? If so, then the investigation starts there. Lift the secondaries...tape them off for safety, refuse, and fire it up. Does the fuse blow? If so, you have a bad transformer primary. If the fuse holds, then re-establish the high tension winding to the rectifier, disconnect the B+ feed from the rectifier and repeat the test. If the fuse blows, you have a bad rectifier...or that high tension winding is shorted. If it holds, resolder that B+ connection and test again...without tubes. If the fuse blows, then you can start doing the work that would have to be done even if a fuse wasn’t blowing before you started the work...the electrolytics need to be replaced.
    If you prove the PT to be bad, I suggest not going to the expense of another PT...unless you want to gut the chassis and build an all tube amp there. If you do that, you could build a 5E5 Pro but using octal preamp and phase inverter tubes so as to utilize the octal holes that are already there.
    Have fun.
     
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