A quick tube (valve) fuzz box

@ Lawry: I just had a listen to the demo clip you uploaded to Soundcloud and I think it sounds great, might have a go at building one since I've got a spare 9-pin valve socket with a shield in amongst my bits and pieces, I also have a diecast aluminium box I could use too.


If you're after some 47uF caps that are rated for 450V you can get them from Jaycar Electronics, I know that you're only getting about 70V, the 450V DC rating of the caps should ensure that they can handle the voltage with ample to spare.

Have you tried using a 12AT7 or a 12AX7 valve in your pedal design?, the 12AT7 and 12AX7 have different gain factors compared to the 12AU7, but they have the same pin connections and therefore should work fine.

Finally got a chance to do some tinkering... and now I too can spend some time in Purgatory!

It's definitely a single coil pedal in my mind. With humbuckers it seems a bit too much or too little to me, whereas single coils seem to work nicely. YMMV.

Here's a quick run down on my build. It's Lawry's version 2 of the circuit (thanks Lawry) but with the addition of 12v/9v switching via a 4 pole slide switch and some extra bits (so that I can use a 9v supply if I don't have a 12v supply set up).

Initial layout showing where track breaks need to be:
Attachment 15280

Track breaks in place:
Attachment 15281

Working out where I can squeeze the 9v extras in on the board (6v regulator and caps):
Attachment 15282
Attachment 15283

Extra track breaks for the new bits (the three on the right) to isolate them from the existing circuit:
Attachment 15284

cont...

Links in place, wiggly left one is the common for the 9v parts:
Attachment 15285

The enclosure I was going to use wasn't as deep as I thought, so I decided to reuse the box from my first ever pedal built several decades ago. The existing holes weren't quite in the places I needed, but I could make it work:
Attachment 15286

Marking out the new layout:
Attachment 15287
Attachment 15288
Attachment 15289

cont...

Implements of destruction... needed for the big tube hole:
Attachment 15290

Holes drilled, filed and hopefully all in the right place:
Attachment 15291
Attachment 15292
Attachment 15293

Quick mockup to make sure everything is mostly right:
Attachment 15294

cont...

More mockups:
Attachment 15295
Attachment 15296

Components added:
Attachment 15297
Attachment 15298
Attachment 15299

cont...

Test fitting board in enclosure (this is where the existing holes made things awkward):
Attachment 15300

A little bracket to hold the board in place:
Attachment 15301

I'm using a tri-colour LED so I can have one colour for bypass and then a colour each for 12v and 9v active:
Attachment 15302

Loom prep:
Attachment 15303

Wiring:
Attachment 15304

cont...

Installing the wiring into the enclosure... normal sensible people do this outside the box. Things are getting tight:
Attachment 15305

Everything is connected, time to add the heatsink to the regulator (double-sided heat tape, then bolted to box):
Attachment 15306

All internals in place, don't ask me how long it took to get the nut on the heatsink bolt:
Attachment 15307
The 4-pole slide switch selects between 12v and 9v supply. For 12v the tube heaters are in series via pins 4 & 5 as per Lawry's build and fed directly from the 12v. With the 9v the heaters are swapped to parallel across pins 4 & 5 with a ground added to pin 9 and fed via the output from the 6v regulator circuit added to the board.

Noise maker installed:
Attachment 15308

Caged up and ready to rumble... hopefully:
Attachment 15309

cont...

Amazingly, it worked first time!

Red on bypass (9v or 12v):
Attachment 15310

Violet active on 9v:
Attachment 15311

Yellowy Green active on 12v:
Attachment 15312

Basically, the RGB LED always has the red on and then either the blue (9v) or green (12v) is added when active giving violet and yellow-green respectively.

Done and done. I was going to paint the enclosure when I first planned this, but now I'm thinking I'll leave it... at least for now.
Attachment 15313

I still need to experiment with the sounds and how it changes with the voltage. It has a little less 'oomph' on 9v but the overall sound isn't that different. I've only tried it on a little solid-state amp so far, but it gave that a bit of tube-ishness which was nice. I used a 12AU7 tube like Lawry's, but may try a few alternatives when/if I get time. Thanks again for the circuit and inspiration Lawry!

Quote:

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Originally Posted by WeirdBits

Amazingly, it worked first time!

Red on bypass (9v or 12v):
Attachment 15310

Violet active on 9v:
Attachment 15311

Yellowy Green active on 12v:
Attachment 15312

Basically, the RGB LED always has the red on and then either the blue (9v) or green (12v) is added when active giving violet and yellow-green respectively.

Done and done. I was going to paint the enclosure when I first planned this, but now I'm thinking I'll leave it... at least for now.
Attachment 15313

I still need to experiment with the sounds and how it changes with the voltage. It has a little less 'oomph' on 9v but the overall sound isn't that different. I've only tried it on a little solid-state amp so far, but it gave that a bit of tube-ishness which was nice. I used a 12AU7 tube like Lawry's, but may try a few alternatives when/if I get time. Thanks again for the circuit and inspiration Lawry!

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That looks wicked, I like the effect you get with the holes drilled in the metal valve shield, gives it a retro-vibe, I'm going to have to have a go at making one of these next year, I still have some spare valves which I can use in my build.

Also, the tri-coloured led is a nice cool touch.

Quote:

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Originally Posted by lawry

And, young Scott, you have mad a deal with the devil. Or at least his Dirty Angel. So be prepared for Purgatory.

Today's phase:
Got me a box and mounted everything inside. (Weird Note: For some reason it picks up more noise inside the box so I'll have to work on that).
However, it's getting closer.

Next step is to come up with some artwork to make the box look perty.
http://www.pitbullguitars.com/wp-con...498k-image.jpg
http://www.pitbullguitars.com/wp-con...1y7m-image.jpg

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One thing you could try doing to get rid of the noise is to connect the metal of the case to circuit ground, the case will then act as a Faraday Shield for all the internal electronics, also, make sure that any shielded audio wire you use for the input wiring has it's shield braiding connected to ground at one end of the wire, this will prevent earth-loops in the input wiring from inducing hum-noise into the input, the control grid of a 12AU7, 12AT7, 12AX7 operates at a very high impedance, meaning that it takes very little current to drive it, as a consequence it tends to be very sensitive to noise pickup.


I'm going to try bread-boarding the Purgatory V2 circuit over the Christmas holidays and see if I can come up with some cool mods to the circuit, I can think of at least a couple that I'm interested in trying out, one mod is to add a 3-Band passive EQ tone control after the second triode gain-stage, you could either use the Fender 3-Band EQ component values, or, the Marshall 3-Band EQ component values, I'm considering using a Mosfet, such as the 2N7000, as a Common Source amplifier stage to act as a buffer for the second triode gain stage so that the 3-Band EQ doesn't present too much of a load to the second triode gain stage, the result should be a tone that is a bit brighter, the other mod is to add an extra gain stage at the front end of the circuit, again made up of a 2N7000 Mosfet, this should increase the amount of gain attainable from the circuit, I will have to check to see if the mods will work as intended though.

Sorry to revive an old thread, but did you ever end up building your modded version Doc? Curious to see how it went if you did. I wouldn't mind having a crack at building this pedal myself

Quote:

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Originally Posted by JohnH

Sorry to revive an old thread, but did you ever end up building your modded version Doc? Curious to see how it went if you did. I wouldn't mind having a crack at building this pedal myself

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Not yet since I've had a few things on my plate lately, but I'll start working on it next month, actually, thanks for reminding me about it.....cheers.


I managed to find a couple of spare 9-pin valve sockets complete with metal shields, one is made from Ceramic, the other one is made from Teflon, I'm going to use the Teflon one to make a 4-Knob Tube Driver pedal, the other one will be used to make a Purgatory pedal, might even do a build thread so that you can see how I went about building it.


Might need to order some spare 12AX7/ECC83 valves from Evatco soon, since I'm running out of good ones, most of the spare 12AX7/ECC83 valves I have are a bit weak in gain.

Here's the link to the Evatco website again, if you're interested in ordering stuff online from them, click on the Products List menu to see what they have in stock:

http://www.evatco.com.au/

Thanks for the link! Will order some bits and pieces today and have a crack at it. If you get the time, a build thread would be great (especially for noobs like me)

Quote:

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Originally Posted by JohnH

Thanks for the link! Will order some bits and pieces today and have a crack at it. If you get the time, a build thread would be great (especially for noobs like me)

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No worries at all mate, hope the link proves to be of some use to you, I may even order some more 9-pin valve sockets when I get round to ordering some new 12AX7/ECC83 valves, I'm going to be ordering some new valves for my 5 Watt Legacy amp later on this year together with a new Jensen C10Q speaker to put in my old Peavey Backstage Plus amp so I can get it back up and running, building a Purgatory pedal may be a good project to work on over the Christmas holiday season come to think of it.

I've got quite a few good projects on my "to do" list, one project that I'm pretty keen on is the restoration project on my Fender Super Twin amp, I reckon that the Fender Super Twin amp is going to be a killer piece of gear for live gigging, I've had a yarn to a local Darwin repair tech about the restoration project, he seems pretty keen to help me out with it, I also have a speaker cab build project planned for it as well.

The Fender Amp sounds like a great project - you should definitely document it here on the forum.

I started getting the bits and pieces for the Purgatory Pedal today, so will have a bit of a play this weekend if I get any spare time.

Out of curiosity, what does the inverter do in this circuit? I've been reading up on them, but to be honest it completely confuses me, and I just ended up reading a lot about oscillator circuits (which was fun, but distracting)

Quote:

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Originally Posted by JohnH

The Fender Amp sounds like a great project - you should definitely document it here on the forum.

I started getting the bits and pieces for the Purgatory Pedal today, so will have a bit of a play this weekend if I get any spare time.

Out of curiosity, what does the inverter do in this circuit? I've been reading up on them, but to be honest it completely confuses me, and I just ended up reading a lot about oscillator circuits (which was fun, but distracting)

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Basically, all the inverter circuit does is it takes the lower supply voltage from the plugpack adaptor and converts, or steps it up, to a higher DC voltage that the valve can use to run properly, even though a 12AX7 valve can work with voltages as low as 12V DC on it's anodes, it tends to work a lot better if the anode voltages are more in the range of 50V to say 100V, the 12AX7 valve was actually designed to operate with anode voltages up to a maximum of 300V DC, that's where it is able to produce the most voltage-gain, by gain, I mean amplification, if you run a 12AX7 at lower anode voltages, the 12AX7 tends to distort in a characteristic way earlier, of course we could replace the inverter with a 240V AC mains transformer that can supply up to 300V DC, but they tend to be a bit expensive and dangerous, using a plugpack adaptor with the inverter circuit works out to be cheaper and safer too.

Quote:

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Originally Posted by DrNomis_44

Basically, all the inverter circuit does is it takes the lower supply voltage from the plugpack adaptor and converts, or steps it up, to a higher DC voltage that the valve can use to run properly, even though a 12AX7 valve can work with voltages as low as 12V DC on it's anodes, it tends to work a lot better if the anode voltages are more in the range of 50V to say 100V, the 12AX7 valve was actually designed to operate with anode voltages up to a maximum of 300V DC, that's where it is able to produce the most voltage-gain, by gain, I mean amplification, if you run a 12AX7 at lower anode voltages, the 12AX7 tends to distort in a characteristic way earlier, of course we could replace the inverter with a 240V AC mains transformer that can supply up to 300V DC, but they tend to be a bit expensive and dangerous, using a plugpack adaptor with the inverter circuit works out to be cheaper and safer too.

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Ah, ok, that makes sense.

Got some tubes in the mail today, so am finally fully prepped to give this a go. As a heads up, I may have to ask a million dumb questions. Apologies in advance...

Finally got to solder this all together today. So far... it’s not working. However, I’m reasonably confidant it’s just a bad solder join somewhere, so will attack it with fresh eyes tomorrow.

It’s been a lot of fun working on this. I’m still very new to reading schematics, and I’ve been enjoying trying to understand what’s actually happening.

Quote:

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Originally Posted by JohnH

Got some tubes in the mail today, so am finally fully prepped to give this a go. As a heads up, I may have to ask a million dumb questions. Apologies in advance...

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Ah that's okay, there's no such thing as a dumb question, they are all valid in my book if the answers help.

Quote:

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Originally Posted by JohnH

Finally got to solder this all together today. So far... it’s not working. However, I’m reasonably confidant it’s just a bad solder join somewhere, so will attack it with fresh eyes tomorrow.

It’s been a lot of fun working on this. I’m still very new to reading schematics, and I’ve been enjoying trying to understand what’s actually happening.

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So what exactly is it not doing?

After a bit of mmmm-ing and ahhhh-ing, I've decided to replace the existing circuitry in my Doctor Overdrive pedal with circuitry based on Lawry's tube fuzz box, that way I can use the existing pots and etc since there's a 250k log, 25k lin, and a 1M log pot already installed in the case, I can re-build the Doctor Overdrive circuit board in another case at a later stage, it doesn't get used much so it's no big deal anyway.


Just been working on drawing-up a version of the Purgatory pedal schematic with some mods that are worth trying, going to scan it into my computer using the scan function of my new HP printer I bought recently, once it's posted I'll explain the mods I did to the circuit.

Here we go:

Attachment 26974


Mods To The Stock Purgatory Pedal Schematic:

* Added an extra 68k resistor to the 1M resistor on pin 2 of V1, this is something you see in a lot of Marshall amp circuits, it's basically a grid-stopper to prevent self-oscillation.

* Change V1 A's cathode resistor from 470 Ohms to 820 Ohms and put a 680nF cap in parallel with it, this increases the gain of the first stage a bit (maybe change the 220k anode resistor to 100k too), this should give a Marshall-like tone.

* Change V1 B's cathode resistor from 470 Ohms to 1k and put a 1uF/25V cap in parallel with it, this will increase the gain a bit more.

* Added Q1, an N-Channel Mosfet, which adds a buffer to the Purgatory pedal circuit to enable V1 to better drive the tone stack, this is similar to what's done in most Marshall amp circuits except that one half of a 12AX7 tube is used to form the buffer.

* Added the Marshall Tonestack to the circuit, this enables greater tonal flexibility, you could also use the Fender Tonestack if you wanted to get more of a Mesa/Boogie tone.


Note that I haven't had a chance to try these mods yet so I don't know how they will sound, but they should work in theory.


Note 2: The N-Channel Mosfet used for Q1 needs to be rated higher than the +HT supply voltage generated by the inverter, most N-Channel Mosfets intended for VHF/UHF applications will also work at audio frequencies too.


Note 3: As Marcel has just pointed out, one other possible mod is to change V1 B's cathode resistor to 39k and omit the 1uF/25V bypass cap to get even closer to the Marshall tone.

Quote:

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Originally Posted by DrNomis_44

So what exactly is it not doing?

---

Well currently it’s not doing anything (at least in the way of making noise lol)

I haven’t had a chance to look at it again as we’ve had people over every night since. I had a brief fiddle with it after I initially posted, and can confirm voltage up to a point. Annoyingly I only have a very very cheap multimeter, which doesn’t have a continuity function.

Hopefully can get back to it tomorrow night

Quote:

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Originally Posted by DrNomis_44

After a bit of mmmm-ing and ahhhh-ing, I've decided to replace the existing circuitry in my Doctor Overdrive pedal with circuitry based on Lawry's tube fuzz box, that way I can use the existing pots and etc since there's a 250k log, 25k lin, and a 1M log pot already installed in the case, I can re-build the Doctor Overdrive circuit board in another case at a later stage, it doesn't get used much so it's no big deal anyway.


Just been working on drawing-up a version of the Purgatory pedal schematic with some mods that are worth trying, going to scan it into my computer using the scan function of my new HP printer I bought recently, once it's posted I'll explain the mods I did to the circuit.

Here we go:

Attachment 26974


Mods To The Stock Purgatory Pedal Schematic:

* Added an extra 68k resistor to the 1M resistor on pin 2 of V1, this is something you see in a lot of Marshall amp circuits, it's basically a grid-stopper to prevent self-oscillation.

* Change V1 A's cathode resistor from 470 Ohms to 820 Ohms and put a 680nF cap in parallel with it, this increases the gain of the first stage a bit (maybe change the 220k anode resistor to 100k too), this should give a Marshall-like tone.

* Change V1 B's cathode resistor from 470 Ohms to 1k and put a 1uF/25V cap in parallel with it, this will increase the gain a bit more.

* Added Q1, an N-Channel Mosfet, which adds a buffer to the Purgatory pedal circuit to enable V1 to better drive the tone stack, this is similar to what's done in most Marshall amp circuits except that one half of a 12AX7 tube is used to form the buffer.

* Added the Marshall Tonestack to the circuit, this enables greater tonal flexibility, you could also use the Fender Tonestack if you wanted to get more of a Mesa/Boogie tone.


Note that I haven't had a chance to try these mods yet so I don't know how they will sound, but they should work in theory.


Note 2: The N-Channel Mosfet used for Q1 needs to be rated higher than the +HT supply voltage generated by the inverter, most N-Channel Mosfets intended for VHF/UHF applications will also work at audio frequencies too.

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Looks to me that you have become an alchemist magician Doc, doing the whole transforming Lead into Gold thing.... or more rather from 'Purgatory pedal' into 'plugin Marshall front end + tone stack'...

Personally I'm surprised you didn't up V1b cathode to 39k .... lol ... ;-)

Quote:

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Originally Posted by Marcel

Looks to me that you have become an alchemist magician Doc, doing the whole transforming Lead into Gold thing.... or more rather from 'Purgatory pedal' into 'plugin Marshall front end + tone stack'...

Personally I'm surprised you didn't up V1b cathode to 39k .... lol ... ;-)

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Now that you mention that, I'm surprised at that little oversight on my part, I'll make an addendum to my post.....cheers mate!


I'm going to try building it with that 39k cathode resistor mod cause I'm intrigued about what it might sound like.


So, the next thing I need to work out is how I'm going to build the circuit, I just happen to have some blank pad-per-hole circuit prototyping board that I recently bought from my local Jaycar Electronics shop, what could be interesting for my build is to do something similar to a Turret board, and use some PCB pins as Turrets, there should be no issues with the + 70V HT exceeding the dielectric strength of the phenolic insulation of the pad-per-hole board, I'm guessing that it can withstand at least 300V DC or so, the inverter circuit can be built on a separate piece of pad-per-hole board.

I found my attempt at this in a drawer today. I think i tidied my studio for some reason and totally forgot to pull it back out.

Anyway, looking at it again tonight I couldn't see any issues, I went over the schematic about a dozen times. Then I realised, I'm pretty sure I've wired the tube socket backwards.

Just to double check, if I'm looking at the bottom of the tube, with the gap between the pins at the top, pin #1 is the first pin to the right of the gap? Because I've wired it as if the first pin is to the left.

Been ages since I thought-up that Purgatory Pedal mod I posted, got side-tracked with some other things that needed my attention.

Quote:

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Originally Posted by JohnH

I found my attempt at this in a drawer today. I think i tidied my studio for some reason and totally forgot to pull it back out.

Anyway, looking at it again tonight I couldn't see any issues, I went over the schematic about a dozen times. Then I realised, I'm pretty sure I've wired the tube socket backwards.

Just to double check, if I'm looking at the bottom of the tube, with the gap between the pins at the top, pin #1 is the first pin to the right of the gap? Because I've wired it as if the first pin is to the left.

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If you're looking at the pins with them facing you, pin 1 will be the one on the left-hand side of the large gap in the pins, from pin 1 you just keep counting the pins clockwise from it.

I think this is where I'm getting myself confused. If I have the pins facing me and start with pin 1 being to the left of the gap, and then go clockwise around, pin 2 would be the first pin on the right side of the gap (see below), but that doesn't seem right.

Attachment 35538

I thought it should be like this?

http://www.dogstar.dantimax.dk/tubestuf/pinout.htm

Quote:

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Originally Posted by DrNomis_44

Been ages since I thought-up that Purgatory Pedal mod I posted, got side-tracked with some other things that needed my attention.

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Ha ha ha, same. Life gets busy

Attachment 35539

(tube socket pins)

Quote:

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Originally Posted by WeirdBits

Attachment 35539

(tube socket pins)

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Excellent! In that case I've just wired the socket backwards, so hopefully that'll be an easy fix tomorrow.

Thanks heaps

Got this wired up today, plugged it in, and poof! Magic smoke from the IC.

After a closer inspection there's a bit of stray solder joining two tracks so I imagine that had something to do with it. Will try again tomorrow with fresh eyes

Good luck. I have liberated a lot of magic smoke in my time. There's no getting it back in either :(
I hope you have spare chips.

Luckily past John was kind to present John, and ordered many chips lol.

I forgot how gross the smell is when you release the magic smoke. Found two other half built pedals in a drawer while looking for the 12v power supply, so will look more closely tomorrow and see what they need to be finished

Oh the dreaded magic-smoke locked-up inside those components, fortunately I haven't had that happen to me very often....touchwood, although one time I did experience what happens when an electrolytic capacitor explodes, first you hear it go bang, and then you smell the aftermath.

Fortunately I wasn't around when this happened:
Attachment 35562

It's on a 30w Kustom acoustic amp chassis I picked for $5. I will try to fix it one day. Or raid it for parts. If I could ID the spring reverb unit on it that might make it into my valve amp build if I ever get around to that.

Quote:

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Originally Posted by jugglindan

Fortunately I wasn't around when this happened:
Attachment 35562

It's on a 30w Kustom acoustic amp chassis I picked for $5. I will try to fix it one day. Or raid it for parts. If I could ID the spring reverb unit on it that might make it into my valve amp build if I ever get around to that.

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Yeah, that looks like a classic example of an exploded electrolytic cap, if you're lucky all you'll need to do is replace that cap and the amp should work again, I've seen an exploded electrolytic cap where the aluminum casing had literally been blown-off, and you could clearly see the insides of the cap that had exploded, it was in a DC regulated variable power supply I had built from a kit I bought from Jaycar Electronics.


If I were you, I'd replace both of those caps with new ones of equal or greater capacitance and working voltage.

Quote:

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Originally Posted by jugglindan

Fortunately I wasn't around when this happened:
Attachment 35562

It's on a 30w Kustom acoustic amp chassis I picked for $5. I will try to fix it one day. Or raid it for parts. If I could ID the spring reverb unit on it that might make it into my valve amp build if I ever get around to that.

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It'd be fun to see if you can get it going again, but then sometimes those projects are such huge time-sucks