#1
The title may be a misleading, but basically my new project for the week is gutting out my old lame Epiphone Studio 10eqx and replacing it with a AX84 Firefly (~1w tube amp). So I guess I'll call it the Epiphly.



Sounds like fun eh?

Anyway, I haven't recieved all the parts yet, so I'm gonna have to wait to build it, but I have most of it layed out. (I plan on making it as point to point as possible, since a turret/eyelet board wouldn't even fit anyway, just some terminal strips, it'll probably look like crap). I'm also gonna have to glue in some wood to hold up the chassis (I'm guessing the combined weight of the tubes, circuit, and pt/ot transformers are gonna cause some problems without some support.)







As soon as I get the pots, jacks, and the rest of the switches, I'll be able to lay everything out and rearrange as necessary then start drilling etc.

Total cost of the project so far
Transformers - ~$60
Circuit Parts (pots, caps, resistors, jacks, sockets, etc) - ~$24

I had the amp and some misc parts like knobs on hand, so I'm calling the total cost of this project ~$85. Not bad I guess. Except I forgot to order a 12au7 tube, I thought I had one, but it turns out I'm wrong. I have plenty of 12ax7's though.
Last edited by greenbox at Sep 11, 2006,
#2
sounds good greenbox, puts that little practice amp to good use, but you might want to put a fan in it, a little amp like that is going to get really hot with tubes in it...
#3
thats gonna be a tight squeeze in there, but i'm betting you'll be able to do it. Deffinetly order a 12au7 and do not, no matter how tempting it is, substitue a 12ax7... i did that and ended up blowing a transformer, the 12au7 has a wierd thing done to it.(as in i forgot what its called, so thats what i'ma say, i did blow a transformer with it however, and you know how expensive good ot's are"
Last edited by XgamerGt04 at Sep 11, 2006,
#5
^^ Yeah, the build notes said do not, by any means, replace the 12au7. Although the other two tubes are interchangable with other tubes.

I plan on building the thing upside down, with the chassis upside down, so the amp will be upside from it's original construction.(does this make any sense?)

This way, the tubes are pointing upwards, so the heat'll dissipate upwards, I plan on throwing in some sort of ventilation, either holes or I'll cut out a section of the rear cover. Though, I don't think this is the final layout, I wanna try and get the tubes lined up at the rear. But then I'd have to figure out where the OT/PT are going. Hmm... we'll see.
#6
I don't see how replacing a 12ay7 with a 12ax7 would hurt...possibly more current draw for the PT? Having a power transformer setup that touchy though would just be dumb in the first place. I don't see how the added gain could hurt?


Try a 12ax7! Do it!

EDIT:
Just realized you said 12au7, not ay. Oops.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
#7
Well, a 12ax7 has 5 times the gain of a 12au7, i'm not sure if that's the difference that doesn't allow you to use a 12ax7 in place of the 12au7

hmm, the 12au7 has more plate dissipation, higher cathode current, larger grid voltages, half the grid resistance, one fifth the gain, 10 times the plate current, 1/10th the plate resistance

I mean, there could be a bunch of reasons. You could probably go with a 12ax7, but you'd get more gain (which I don't actually want), but you'd probably need a different output transformer.
Last edited by greenbox at Sep 11, 2006,
#8
Yeah...seems to me that would just clip the output stage though.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
#9
my best guess: the 12ax7 has different resistive characteristics that would burn your output transformer the same way that connecting a 160ohm speaker cab to your 8ohm amp might damage your amp's output transformer.
Last edited by greenbox at Sep 12, 2006,
#10
Wait what?
I guess I need a schem...it sounds to me like you must be using the 12au7 as a "power" tube!?
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
#12
Just read the first post...oops.

This would be a good project if you had some salvaged transformers.

Nice and simple.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
#13
I wanna see this! i have an old small amp enclosure that i was thinking of screwing around with so this might give me some inspiration.
Marty
#14
Theres not much heat really generated by the tubes at all, mine is in a small enclosure and it never really gets to hot. The reason you cannot interchange the two tubes is that the way it is set up the 12au7 is a powertube. It is made where i can be ran as a push/pull tube, whereas a 12ax7 does not have the luxury of being able to do that as well as a 12au7. It is also because the 12ax7 has a higher gain yes, that messes with the transformer, all i know is that my experiment fried an OT
#16
Wow, pretty damn cool project, can't wait to see the finished thing.
"Breathe, breathe in the air
Don't be afraid to care"

Fender Strat/Tokai LS80>few pedals>Orange Rocker 30
#17
any progress?
Quote by rabidguitarist
I even tried dressing up as a fly myself, and throwing myself out of the window in the hope that they will follow me. But to no avail.

Quote by daytripper75
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#18
a little, i'm still waiting for the majority of the circuitry parts, but I'm currently drilling the chassis. Or atleast waiting for the battery on my drill to charge so I can start drilling.

I'll post pictures up later.
#19
so are you just using the original schematics, or are you gonna add the volume mod or attentuiator(yes i can't spell that but i'm sure you know what it is"?
#20
oh, i'm just going by orig. schematics, which is fine, since I barely have space for the pilot light (in fact, I don't have space for the pilot light I currently have, hmm... I'm gonna have to figure out something creative.)

anyway, the conrol panel (which will be on the bottom of the amp.

Input - Volume - (non-existant pilot light) - Boost Switch - Boost Knob - Fuse - Standby - Power
#22
Looks good greenbox
Quote by rabidguitarist
I even tried dressing up as a fly myself, and throwing myself out of the window in the hope that they will follow me. But to no avail.

Quote by daytripper75
we have a Llama forum, and still no drum forum.
#23
Oh, just in case anyone's a late night browser (unless you don't live in the US, I've no idea what time it is.), I found a place for the pilot light (kinda a bad place but... whatever). And I mounted the power transformer. At some point in the future, I'll mount the output transformer and the tube sockets.



Last edited by greenbox at Sep 16, 2006,
#24
Looks good.

In need of gut shots.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
#25
Haha, there's nothing in the guts right now, but as soon as I start mounting/wiring stuff, I'll be sure to get shots in.

Although, I'm gonna have to do alot of planning since everything's gonna be wired as point to point as possible, with maybe a terminal strip. It should'nt be too bad, hopefully, since I'm pretty tight on space.
#26
do alot of planning for it since its that small of a space, and when your done planning plan some more, you might not need to shield much wire in your build since its in such a small area. I know that my firefly has the input jack right by the first 12ax7 so i don't shield the line to it
#28
Alright, I realized a few things. Tight spaces = bad. There are numerous things you can't get rid of unless you try REALLY REALLY hard. My best guess is that since I didn't exactly use the best insulation for my leads (I wired point to point, and used... i think it was 200v insulation on the leads), along with a combination of the inherent capacitence in the wires, at high gain levels (just right at max volume, or with the boost on max, at around third of the way). There's a high pitched squal (oscillation). I could theoretically rewire everything to fix it, but seeing as how I don't mind that I can't dime this (which I wanted as a quieter practice amp for my apt) I think it's acceptable on my end.


Gut shots, ~50% done.


Gut shots, 100% done. It's really messy at this point.


Finished shot on the back.


Finished shot on the back with back cover (but without the tube covers, I was too lazy to put them in the shot).

Anyway, I'm fairly happy with it, it's a tad bit quieter than my champ, and cost me less than $100. Whoo?
Sound clips eventually...
#30
Jesus Murphy that looks complicated.

Honestly, I'd love to build myself an all-tube practice amp, but I would have no clue what to do.
#31
i see radioshack solder, did you sheild input lines and the line from the volume control/gain control, it sounds like the problem is somewhere in there to me. Or either you've got a ground loop. I think wiring would be the last thing, but nice job, alot neater than my firefly
#32
It's star grounded, so I don't think it's a ground loop. I tried messing around with the lines from the input and volume control gain, so it's *likely* that that's not the problem (they usually don't have to be shielded unless you have good lead dressing... then again, the lead dressing in that small space is pretty horrible I'll admit.)

The point is, I'm too lazy and therefore unwilling to fix the problem. It's not like I'm gonna sell this amp or anything, so I'm okay with it.
#33
nice job though man, it might be the lead dressing then. Looks better than anything i can do point to point. Laziness is just telling you to stop lol, i didn't listen one time, and boom my amp was up in smoke...