I never really appreciated that amp like I could have - I was young and dumb... My friends all made fun of it. It had a gnarly, sparkly silver grill with a horrendous red racing stripe. And contrary to the notion that the bass player was supposed to have the biggest amp - it only stood about knee-high.
We called it "The H-bomb" - and I did terrible things to it. I took a saw and cut the top off so I had a "bass head", then mounted the speaker in a huge poorly constructed plywood cabinet. I would daisy chain my friends amps into it and blast the poor sucker so it would be louder... All that and more. It just never satisfied.
10/29/08 - UPDATE: I got curious and did some research... My amp was an H525. These pics from the Harmony Database really take me back (and make me want to weep for my stupid younger self). Mine was in slightly better cosmetic condition when purchased. What I wouldn't give to have it back...
Eventually I acquired a slightly newer and more suitable amp for my purposes, and the H-bomb was retired to the depths of the closet. Until one day...
Our rhythm guitarist blew out his Hohner solid state in the middle of practice one day, so I drug out my old Frankenstein rig. Man - talk about an ear opener - we had never heard tone like that except off a record! Chunky saturated overdrive - just the way it was supposed to sound: not fuzzy or buzzy at all. Dumb ol' me: I GAVE THE AMP TO HIM, because after all, I was a bass player and had no use for a guitar amp.
~~Heavy Sigh~~...
That was years ago, but ironically not as many years as I've been telling myself that "I could build an amp." So the time has come to give it a go.
A few years ago I started educating myself in earnest, on tube amps and what makes them tick. I was so hungry for information that I'd pick up pretty much anything that had "tube" and "amplifier" in the title or between the covers. When I grabbed Dave Hunter's "The Guitar Amp Handbook" off the shelf at Borders, I had no idea there was a complete how-to project inside - that was just bonus, and ultimately the reason I paid up and took the book home.
I began sourcing parts in Jan 08 and told myself I wouldn't begin the project until I had every last component: I didn't want to get hung up and have to sit on my thumbs waiting for someone's back-order to ship. Now that everything's in place, I can start turning this pile of stuff into a functioning amplifier.
As I was sourcing parts, I discovered other Two Stroke projects on the web. I got caught up in re-thinking the project in terms of other's (and Mr. Hunter's as well) mods - and so got sidetracked into thinking I might wind up missing something if I didn't build the "current version" of the amp. But I've been down that road before - I woke up and decided to stick to the original plan: build the amp in the book. I can always mod it later if I want, or (better), build another (no such thing as too many amps!).
So, here we go. DISCLAIMER: This is not a "how-to" - I'm just sharing my experience of the build. If you follow any procedure or practice that I do because you learned it here and lose an appendage or electrocute yourself, you and your heirs are on your own. 'Nuff said?
Challenges I hadn't considered and which were not addressed in the book became apparent even as I was obtaining parts. I had a box of guts but no chassis (I intended to bend my own and save $30), I had no "good" way to bend a chassis. I had no cabinet (I intended to build my own and save over $100) to mount a completed chassis in... Arrrgghhh!!!
I decided to start at the end and work forward: cabinet first, then chassis, circuit board, etc... I got a 4x8 sheet of 3/4" birch plywood at the H.D. and had them do the rough cuts. I ripped the top, bottom, sides, and back brace to width & sized them to final length on the table saw at home. At this point everything came to a screeching halt because I still hadn't decided what joints to use. Box? Finger? Dovetail? Butt? You'd think I'd have thought of it before then...
I decided on dovetails because I liked the idea of their strength and relative ease of assembly. I also happened to have a dovetail jig to use with my router that the wife had picked up for me at a garage sale years ago. I set it up, and - @$#%!&*!!!!! It's only wide enough for 8" panels. My cabinet width is 9". Crap.
Off to Harbor Freight to pick up a 12" jig. Yay! A sale! 20% off tempered the hiccup a bit, plus I'm a sucker for new tools.
I'd never cut dovetails before... So it took a while to get the knack - a week later and I'm proud to consider myself a novice at using the jig:
Not too shabby. They seem a bit tight, but they go together without damage (even though I gotta knock 'em together with a hammer) and they don't come apart except by force. I had dug out my bar clamps in preparation for assembly, but ultimately didn't use them. I applied glue, knocked the joints together, and voila! Don't let the apparent shallow depth of the dovetails fool you - these joints are strong.
It's even SQUARE!! Another happy moment...
Next, I cut the cleats for the baffle board and back brace out of poplar and installed them:
Then I cut the speaker holes (one 8", one 10") in some 1/2" ply. I purposely used construction grade 'cause I don't know if I'm gonna keep this speaker configuration - and I don't have the resources to waste good birch plywood...
Now it's time for the control panel cutout. I sweated this for a few days - I wanted to get it right the first time, so I took my time, used a fence,
And still managed to muck it up. Don't ask. Let's just say it was one of those "What the *&^%# are you doing?" moments - as I steadily continued doing the thing that made it worse... HINT: Dull jigsaw blades like to heat up and go Gumby on you when it's most critical that they don't.
Funny thing about time: even when there's not enough of it to do things right the first time, there's usually plenty left over to do them again... I plugged the hole and:
Whew...
That's pretty much as far as I can go on the cab until I get the chassis bent - I wanna make sure I get all the dimensions/clearances jelled before I start any finish work.
From day 1 (buying the wood) until now has been roughly a month. That's a long time to build a box! But I've been loafing a bit as well - life intrudes sometimes. I'm also trying to move as carefully as I can. It's hard though... you can plainly see the results of my "getitdonerightfreakinnow" nature on the control panel cutout. I won't sweat the time so much in future - I wanna be proud of it when I'm done, instead of making excuses or wishing I'd done something different.
Now it’s time to revisit my youth and see if I really earned that “B” in Mr. Wilkinson’s metal shop class… (“B”?? Who the hell gets a “B” in metal shop? Band geeks. That’s who!)
I could have easily bought a ready-made chassis: pre-drilled, labeled, etc. But there’s no fun in that. I bought a sheet of 12”x18”x1/16” steel at Home Depot. Now it’s time to mess it up.
I looked at a lot of projects on-line, but only found one where the guy bent his own chassis and included a “how-to”. I read, re-read, and re-re-reread his procedure to refresh my memory and jell all the crap I was gonna have to think about in my mind. He used a brick and a hammer as a sheet metal brake. I’m one-up on him with my spanking new bending brake.
The biggest challenge I had forgotten (no wonder I got a “B”), and which my ‘net guru didn’t address, is making sure the dimensions of the bent box come out to what they’re supposed to be. Bending metal ain’t like cutting wood – if you measure a 12” length on metal, and bend it right on the line, the inside dimension will (should) be 12” or very close to it. But the OUTSIDE dimension will be greater than 12”… How much greater depends on the thickness of the metal and the radius of the bend.
There’s a tried and true mathematical formula to use on 90 degree bends (which I’m using): Distance from the bend line to the mold line = inside bend Radius + Thickness of the material (D=R+T). All fine and well, if you know the inside bend radius – which I don’t… So, after some tips and hints from my good ol’ Dad, I decided that as long as I used a “shoe” (or stop, to bend the metal against) that was as close to 90 degrees as I could get, I wouldn’t sweat it much. The first box I make will then tell me all I want to know to make a “precision” chassis in the future. For now, close is good enough – I’ve wasted enough time.
Having said that: I’m pretty famous for “driving by Braille” and just jumping into a project, discovering and (sometimes!) solving problems as I go. Since I wanted to have FUN with this (not wind up pissed off and dissatisfied), and because I’ve deluded myself into thinking I may want to build another amp sometime, I decided to proceed cautiously and actually make a template to lay out the bend lines.
It’s funny the things you remember sometimes… As I was cutting out the first template, I discovered that I’d forgotten to include mounting tabs in the layout. A completed box of the design I had would have resulted in a pain in the ass for me, necessitating adding jury-rigged mounts…
What was so amusing?
Wayyy back when I was a dumb kid, I somehow scored a position in a high-end custom cabinet shop. It was a small operation and the brothers who owned it were meticulous craftsmen. They would often spend as much time (if not more) making plywood jigs and fixtures for a door or panel than they would actually making the damn door or panel. Sometimes the procedure ended in flying tools/material, and lots of cussing. Showing my ignorance, I asked why, if it was such a pain in the ass, did they bother? The answer: “’Cause plywood’s cheaper than ash or oak.”
I wasn’t wholly satisfied at the time (I thought he was being a smart-ass). But NOW I get it! You’re right Dave. Poster board is cheaper than steel. Thanks for the lesson.
After all that – here’s the completed template:
I marked all the corners with a spring-loaded punch and scribed the bend lines in the sheet metal with a nail I sharpened on the grinder… Here’s the transferred pattern. Sort of… This is the best pic I could get with my cheesy camera:
Now it’s time to cut! Slow and easy with a metal cutting blade in the jigsaw… I cut freehand but was v..e..r..y.. careful.
The fruit of my labor and care: the completed cut blank, ready for bending. Not bad!
I finished cutting last night and have suffered at work all day today, anticipating tonight’s activity. I’m so excited I’m about to pee! Getting ready for the first bend…
Now for the other end…
Before I can bend the sides, I have to figure out how to keep the edge of the end tab from striking the end when I fold it up. I had pre-planned for this when I did the layout, but the idea I had at the time wasn’t gonna work…
I solved the problem at the drill-press – cutting the inside corner out to provide relief for the bend. I was making so much progress so fast, I forgot to take pics when I bent the mounting tabs – but as you can see in the upper left, I got ‘em.
Another %@$#*&^! issue when I bent the sides up… I neglected to consider that the end tabs would limit the brake and not permit me to make a full 90 degree bend.
I am constantly amazed and amused at just how many of life’s little problems can be solved with a block of wood and a hammer…
Riveting the end tabs. This isn’t my first choice to secure the tabs, but I don’t own a spot welder…
A new factory built chassis would have cost me $40 + $11.00 shipping. But now that I’ve got this one under my belt: I’ll never buy another metal box again. Below: Fourteen and 1/16” X Six and 1/16” X Two and 1/16”. Cost: $29.99 for the brake (which will eventually “pay for itself”!), and $6.23 for the sheet metal. I saved fourteen bucks out of the gate!
Thanks Mr. Wilkinson (even though you only gave me a “B”!), thanks Dad, and thanks Harbor Freight!
Now that that’s all done I can get bizzy drilling holes in my shiny new box. I’ve learned a valuable lesson, and templates are my new best friend! Preparing to mark the chassis:
I used a step-bit on the drill press to cut the bigger holes.
Yay! Here’s the (mostly drilled) chassis in the cab for a test fit. It’s not as crooked as it looks! Darn shadows...
Now it’s time to fit the transformers. The OT was easy – two holes, surface mount, & two larger holes for the wires to pass through to the interior – no template needed. But the PT is a different matter since it’s mounted on its side and part actually protrudes down into the chassis. Need a big square hole for that. Template time again…
I tested the template on a piece of poster board to check for fit before I marked and drilled the chassis. Good thing too, cause it needed adjusting!
Here’s the adjusted template in action:
After drilling – not bad. Hey – are those holes out-of-round? What the ^%#$’s up with that?
After cleanup with a file. Hmm.. Not my best work ever, but it'll do.
Trannies installed for a photo-op. Hey that sounds like... Uh... Never mind.
That's it for the chassis until it's time to fit the circuit board. Before I get ahead of myself though, it's time to finish up the cab.
I mounted the speakers for a test fit - looks like I'm gonna have to shave a cleat:
I'd been worrying about clearance between the output transformer and top speaker, but my cipherin' paid off with plenty of room to spare.
I wanted to route the edges with the same 1/2" radius as the rest of the amp but my bit was too long... I had to make a jig out of some scrap MDF. I secured the work piece to the jig with hot-melt glue & then peeled the glue off when I was done. Worked like a charm.
Dang! The groove isn't consistent with the radius of the routed outside edge. ~Sigh~ Saw, knife, and file to the rescue...
Now I can start making some real progress, but first, here's the back with everything in place just to give you an idea of "where I'm at":
Here's the front side after laying on the vinyl. The adhesive is pretty forgiving as long as you don't apply pressure to the pieces - it was easy to make adjustments and make sure the vinyl was laid correctly. Once in position, however, you need pressure to get things to stick together. I used a rolling pin I made from a length of 1" dowel faced with craft foam (that blue stick thingy in the pic).
Once I got started I lost interest in taking any pictures. My mind was occupied with folding corners neatly and worrying about how to deal with the vents. I knew I'd have to make some crafty cuts but wasn't sure how. Then I saw a pic (I can't remember where...) that gave me a good idea of what I needed to do - lucky thing, otherwise I'd have botched it for sure. Didn't turn out too bad at all:
Now for the main event: the cab itself. I decided to do this in four sections, using the piping grooves as boundaries. It gave me a chance to practice as I worked, plus the added benefit of allowing me to take a break if I got frustrated. I cut each piece a slight bit longer and wider than I needed. I drew an index line downwn the centerline of the cab (lengthwise) and on each piece of material to guide me while I applied the vinyl and keep it straight.
On with the show - aligning the index lines. Hey wait - there's two index lines? WTF?? I chose the one on the right and got lucky. My friend Henri took these next few pics while my two hands were busy. You can tell 'cause they're slightly out of focus. Thanks Henri!
Pressing the ends into the piping groove with a screwdriver.
And trimming with a carpet knife. You may have noticed the focus improved, but not because I actually did grow an extra pair of hands, and not because someone else took the pics. Henri was kind enough to inform me that I'd left the camera lens on the macro (close-up) setting the last time I'd used it - ironically just before I handed it to her. Good thing I had the knife. Thanks Henri!
Henri left in a huff, so I'm back to one-handed photography again... Using the rolling pin to press the glue together. Keep in mind this is contact cement: when it sticks, it sticks. All I'm doing is applying pressure to an already flat, unwrinkled surface. If there were wrinkles or bubbles in the vinyl I'd have to peel it up and lay it out flat again - an undesirable and difficult thing to do.
The control panel cutout promised to be a challenge but (I thought) perhaps not as difficult as the vents. I was wrong, and I don't know why. Some of the cuts were a tiny bit too much... You probably wouldn't even notice the flaws unless you were critiquing the cab or inspecting it before a purchase, but I know they're there... Despite that, it turned out real nice. I used some black piping to hide the few "too deep" cuts. Turned out to be bonus - I like the look:
Now for the corners. Ugh! I hate corners. I hate wrapping presents and packages. I hate corners.
Say... Not great, but not too bad either!
Besides, nobody's ever gonna see 'em anyway... They call these corner "protectors", but I'm not fooled. They were invented by another guy who hated corners too. Hats off to ya buddy - let's grab a beer sometime.
Then stretched and laid the line in the groove. I used another "rolling pin" to press it down into the groove and hold the ends of the vinyl covering in place. I still haven't grown that extra pair of hands... Good thing Henri cooled off enough to take a few more snaps.
Dang!
Dang! It's probably not a big deal to some, but I'm flippin' out - it looks like the real deal on an amp you'd buy at the store - not cheesy or "homemade" at all. Dang!
Whew! I got a little excited and decided to assemble everything I had to get a preview of how the finished amp is gonna look. Here she is so far...
Now all I gotta do is put the grill cloth on the baffleboard & the cabinet & chassis will be complete, freeing me up to begin the amplifier itself. I'm starting to get excited now - gotta remember to take it easy.
It's been a little while - been proceeding slowly and carefully but the caution has paid off! The last time out I left off with the cabinet and chassis completed - now for the finishing touch: the baffleboard.
I'm a "frugal fellow" (AKA "cheap bastid") so when I saw the prices for grill cloth on-line I was kind of put off. Several trips to local fabric stores were pretty disappointing... "grill cloth" isn't something that just sits on shelves. Basic economics applies, and the result is that the stuff seems to be a specialty item, and so is costly no matter where you find it.
Henri found some fine nylon mesh that I at first rejected, but took another look at after we couldn't find anything else. I discovered that by layering the mesh I could achive the "look" I desired so I happily plunked down $2.50 for 4 yards of the stuff (as opposed to $16.00 and up plus shipping for a single yard of "real" grill cloth).
A bargain to be sure, but what a pain to work with! To achieve the desired look I had to use 15 layers. I spent like a half hour cutting 20"x 20" squares of this gossamer fabric that kept wanting to slide off the table every time I let go of it. THEN I had to stretch each layer before stapling. If you count each "stretch" as a step, a normally 8-step process became a 120-step process! What a way to spend an evening...
Trimming the excess...
Applying the piping. This can be nerve wracking - keeping it straight is harder than it looks, but I persevered.
Wow - I'd say it was worth the extra time. Looks real sharp! I tried this shot at about 50 different angles but still kept getting the glare from the flash - the nylon doesn't absorb light too well. This is the best shot. Ironically, as I write this it occurs to me I could have waited 'till morning, opened the blinds, and took the pic without the flash...
And now for our main feature:
Back in the Olde Days they used to make amps by wiring them "point-to-point", that is, each component was literally soldered directly to each other to complete the circuit. It's a lot of work and can get confusing unless you know what you're doing, and unless you really take the time to make it pretty it just looks like butt...
Moving forward to the plain Old (without the "e") Days, industry moved the components onto circuit boards to make it neater, faster, and easier for unskilled worker bees to produce amps for the masses.
I could have bought a circuit board from a kit supplier, but I wanted to make make my own. Step 1 is laying out the components to create the "flow" of the circuit. Luckily for me I didn't have to think very hard on this - I used the circuit layout from the instructions in the book. All I had to do was make sure the parts fit on the board.
Top: hand drawn template. Bottom: final template after making it pretty on the computer. I might not have bothered with "the pretty one", but I may build another one of these someday - if I do, I can save myself some work...
Now it's time to cut the board material. There's a whole wide world of stuff out there that can be used for this. I chose "G10" epoxy resin fiberglass sheet because it was tough, fire resistant, and cheap compared to other materials.
I found that "G10" is very durable. The pic below was taken on a break from cutting the material. What's this stuff made of? Kryptonite?
I'd thought to be done by now... To heck with it - I broke out the Big Gun:
Geez... O.k. - now that's done. Next I marked the board using a further-refined template. I used the same punch I used on the sheet metal - worked like a charm!
The blue dots are where pass-through and mount holes will go. There were a lot of divots to choose from so I wanted to be sure I knew when to change the drill bit.
Making holes...
And done!
Sorry to disappoint, but I won't be breaking out the pretty green acid for this project since this isn't a printed circuit board - as you can see there's no copper to etch.
This board is more or less simply a mount. Instead of copper traces I'll connect the parts to one another on the top side, and use actual wires to make other necessary connections on the underside. I could proceed directly from here - placing components with their leads through the holes and soldering them together, but industry once again has devised methods to change things up.
The two most common connection point "helpers" are eyelets (simply small brass grommets) or turrets. Each are equally suited to the purpose, but turrets look cooler, so that's what I'll use.
The turrets are secured to the board in a fashion similar to rivets, so I need a tool to mushroom one end to hold them on the board. I could buy a "staking tool" for $12-$15, or I could make one for about 20 cents. Guess which one I went with?
Step one was simply centering a bolt in the table of the drill press and drilling a hole of the appropriate diameter and depth to serve as a "reservoir" for the turret (circled in red).
The turret is placed in the reservoir head-first, with the foot end through the board to be staked (stake? stoke? stoked?). Using a bolt for the resevoir offered the advantage of being able to raise and lower the works to any height I desired making it easy to insert supports for the board.
I could have opted to do this by hand with a hammer and stake, but I used the drill-press as an arbor-press instead cause it's much more impressive. The stake is just a carriage bolt with the head cut off and one end ground from center to edge at about 45 degrees to form a cone shaped protrusion. Insert the turret foot through the board, then the head of the turret in the reservoir, lower the stake and apply pressure. The stake squooshes the foot out and secures it to the board.
Don't be too impressed - the tool I made is exactly the tool I could buy, and the process is simply how it's done. I will however take credit for saving $14.80!
The completed board:
Now it's time to load this baby up.
The book recommends (and after having done it, so do I) "dry fitting" all the components before breaking out the soldering iron. Here's everything arranged before cutting the leads to length.
Good thing I did the dry fit: I initially placed some wrong-value resistors in the wrong places... Anyway - here she is soldered up and with tentacles, ready to install in the chassis.
Wow! Looks like an AMP!
Next two pics - view from the bottom of the chassis to the top:
I did have an issue on the first power-up - I had a bad volume pot installed and had to replace it. Now everything's up and running as it should be and as you might guess, I'm spending quite a bit of time patting myself on the back.
I'm a little disappointed in the distorted tone: it sounds harsh and cold, versus the smooth, warm character I was hoping for. I'm also experiencing a phenomenon know as "ghost notes", where an audible, fuzzy, slightly out-of-tune buzz rides on top of the fundamental note.
UPDATE: I resolved the issues above. There was nothing wrong with the amp at all! My problem was a condition known as "cone cry": I had tightened the speaker mounts too much, distorting the frame and causing the internal speaker components to rub against each other.
NOW I'm in heaven! This thing sounds as amazing as I'd hoped! Oh, my, my...
Now comes the part where I wax philosophical and get all misty-eyed:
Here's something I learned:
If I'd had the resources, I could have done this when I was 10 (perhaps not so well, but I could have done it). The mechanical aptitude was either inherited or learned from my dad. The hard stuff - the patience and attention to detail are learned behaviors that have simply served me well at this point in time. The point is that I waited 35 years to do something I desperately wanted to do.
The lesson (and I particularly hope some of you are paying close attention - you know who you are...) is DON'T WAIT. Not another minute.
If you chase your dreams, you'll chase them forever. Realize your dreams and make them come true. Nobody else is gonna do it for you. And life is just too damn short.
Thanks everyone, for allowing me to indulge myself and for being interested enough to check out my progress.
PH
