zacksamp

Features:

50 watts, dual 6L6 output
I'm reusing the power and output transformers from a Wurlitzer organ.

Fender 'blackface' preamp circuit
Almost all of the fender circuits from the mid 60's had the same if not similar preamp circuits. The main difference was in the poweramp. The circuit we're using is that of a Twin Reverb, Super Reverb, Virbroverb, or Bassman minus the vibrato and reverb.

Tremolo
Tremolo ( in this circuit) sounds as though you are turning the volume up and down..it pulses the amplitude. The Vibrato tube actually oscillates and changes the volume of the amp fast or slow depending on how the controls are set. Some tremolo circuits vary the pitch instead of the volume.

Reverb
Tube driven 2 spring reverb. The 3 spring reverb is a "better" sounding reverb and more like the spring reverb in a recording studio, although the "sloppy" twang of the two spring unit is how all the old fender (and many other makers) revebs sound.

Negative Feedback
A circuit in which the signal from the output transformer is fed back into the last stage before the output tubes. This flattens out the frequency response of the amp, giving a smooth and firm sound with solid bass response. Fender used a lot of this effect to acheive a clean and bold sound. The opposite is true for Vox and other amps with no Negative feedback. The sound of no negative feedback is more high end harmonics and earlier distortion. Basically louder, brighter and more sensitiveity to touch and playing style that Vox is known for. I'll be putting in a switch so this amp can have the standard fender amount of NFB or be switched to no NFB.

Master volume for gain structuring at lower playing volumes
When you turn a "clean" tube amp up towards the top of the volume dial you get some distortion, some amps distort more than others of course. If you need to play quieter a master volume will allow you to turn up the preamp and not blow the roof off. This allows you an amount of distortion you want, at the volume you want. The master volume amps are poo pooed by vintage fender buffs, but are handy feature if you need less volume and a good amount of distortion.

Fender/Gibson style T.V. front combo cabinet
This amp is being made for clean to bluesy tones, we decided to give it a vintage look with all the controls on the back. Pine was used to build the original fender amps. It was cheap and it turned out to sound good as well. Nowdays you can't find as good of wood as back then but luckily you can get close.

15" speaker similar to a Fender Vibroverb
A bigger single speaker gives slightly bigger bass and has a different response your playing dynamics.

Tweed covering
A little ambitious for me since I have never covered an amp but I've done some research here so I think it will be fine. I'll be aging the tweed with amber shellac, maybe bleaching it before as well. I figured it would take less time to age it than putting cigarettes out on it and using it in a smokey bar for 50 years+

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Working out the circuit layout on paper. I used the Twin reverb layout since it already includes reverb and tremolo. Since this circuit is only going to have one channel I just cut off the first channel from the fender layout.	The wood. 1" x 12" "Pine" (spruce) and 1/2" Birch plywood. Wood is so expensive these days...my god!
Making big stuff smaller Cutting the boards down to the proper length on the table saw. The wood you buy in the hardware store is called a 1"x12" although what you actually get is 3/4" X 111/4" The logic is that it starts out as rough lumber and once it's planned smooth and straight you get what you buy in the lumber yard. Kind of like how most products are shrinking and they charge you the same price. Then they say "30% more..".when it has actually just shrunk 30% in size over the years ...don't get me started.	Some jerk! ...looking like my fingers are about to be cut off. Kids, don't ever try to take a picture of yourself while using power tools!
Here's what Half blind dovetails look like before gluing. They inter-lock to form a strong joint between the two pieces of wood. Add glue and you'll never get them apart!.
Dovetails! Setting up the Dovetail template and cutting a test joint. This is a half blind dovetail jig. The dovetails on the top piece don't go all the way through to the top. (You only see the dovetails on the side)	Perfect dovetails! Yeah right!... the thickness of the scrap test cut wood was not the same as the wood I was using and they all came out wrong the first time! It all worked out ok in the end. I had a change of plans and ended making the cabinet a few inches shorter and 2 inches narower. Pine is hard to cut perfect because it's so lightweight and splinters easily.
All glued up and checking for square. The cab is on it's side here. 24"h X 22" w It's kind of a mad rush to get the glue on all the pins and tails and then get everything together and fitted correctly before the glue dries.	Cutting the front panels to make the T.V. front look I was a bit sketchy cutting these. No matter how you slice it there need to be four pieces that make up the front panel . I'm going to dowel all these together to make the panel stronger. The Jig saw always cutts pretty rough so I'll have to spend a while with a file to get these curves to look nice.
Rounding the edges I used a 1/2" roundover bit in the router to make the radius on the edges of the cabinet. I'd like to get even more curve to it but the wood is only 3/4" thick. I didn't want to compromise the strength of the box, plus I only have a 1/2" roundover bit!	Putting the panels in Here are two of the four panels temporarily in place to measure for the cuts on the straight pieces.
Hence the "T.V." front! This is why it's called T.V. front. Here we have all 4 front panel pieces temporarily in place. Just need to glue in the panels, clean up some sloppy cuts and round the edges up.	Slanted view It's a bit hard to tell here but the front of the cabinet is slanted. The top measures 9 3/4" deep and the bottom is 11 1/4 " deep. This slant helps the sound to travel up towards your ears instead of toward your knees and horizontal along the ground. It also helps cut parallel reflections in the inside of the cab. Although this is negligeble in an open back cabinet...
Gluing up the front panel I used dowels and glue to connect the panels together. I bought a 1/4" dowel rod from the craft store and cut it up into 1 1/2" pieces, which were crimped with pliers to let the glue get around the dowel and it's mating hole. The holes were drilled freehand (not recommended) so lining things up was a bit sketchy. Add that doweling jig to my Christmas wish list. My orbital sander gets a workout every time with these sloppy glue jobs! I had to guess about how the Fender amps were made, I assume they were done somewhat similar to this.	I clamped the whole thing to a flat table surface to make the glued pieces as flat as possible. Once the glue is dry I can file, sand and shape the curves and straight lines of the panel. After shaping them it will look a lot better. I'll glue and dowel the finished panel to the body of the cabinet as well. This will help in being strong enough to hold the 15" speaker.
Here's one of my secrets to a holistic amp aproach Giving the power transformer something to do until the chassis is under construction is very important! Not only does the transformer feel useful but it's weight is perfect for holding down the corner of the glued up panel where a clamp won't fit. This way the electronic parts aren't left out of the process of building the cabinet., and jealousy isn't an issue.	Some parts patiently waiting for the chassis to arrive
Doweled front panel I pinned the front panel in with dowels to add strength to the connection of the front panel and the body of the cabinet . Since the speaker baffle mounts to the panel it will need to be as strong as possible. It pains me to drill 1/4" holes all over the cabinet for the pins/dowels but since the cab will eventually be covered in tweed cloth they will never be seen.	Rounded front I rounded the front panel with the same 1/2" router bit that I did the rest of the cabinet with. The grill cloth and speaker baffle will butt right up against the inside edge of the panel. The inaccuruate saber saw work I did on the rounded parts of the panel smoothed out a lot with the rounding of the edges. There are still a few small cut marks that I need to fill and smooth over but since it will be covered in the end it's no big deal.
So far so good.	The parts order showed up! I ordered from three different companies this time.The pots, resisistors and small caps I got from Mouser Electronics, shown here. The bigger caps and some specialized amp parts are coming from Antique Electronic Supply
Drilling the board with the component layout The circuit board here is made from G10 (epoxy and cloth). Basically fiberglass... I used the Fender Twin layout taped to the board as a drilling template with 1/8" holes. Generally one would use a drill press to do this...I don't have one...Hint Hint!	Installing the eyelets After drilling all the holes I inserted the eyelets and flared out the back of them with a phillips bit and a hammer, this way the eyelets are locked in place. The components are soldered to the eyelets as per the schematic and parts layout.
Inserting the components The large caps are still in the mail but I put in the resistors and small caps. Double checking your parts values at this stage is helpfull. I always get excited and overlook simple mistakes!	Soldering everything together The next parts order showed up with the big caps and various other components. I made the mistake of ordering 400 volt caps but it seems that they will do. All of the capacitors on the board only need to be 400 volts or under.
The circuit board is nearly complete I ran out of hookup wire, so I'll have to order more. I will be ordering larger filter caps as well. There's always something you miss the first time	The chassis should be here soon. I'm sort of at a standstill until it gets here. Oh well, I need to focus on Christmas a bit anyhow.
Cutting the transformer holes The chassis showed up just before christmas. It came with mounting ears but I cut them off, it wouldn't fit in the cabinet with them. I had ordered it without them but luckily I was able to make it work. I recycled the power transformer and when I took it out of the original chassis I make this template of the mounting holes. Pretty smart huh?	Drilling the outline I drilled the perimeter of the transformer hole and used a jigsaw with a fine tooth metal blade to cut the hole square. The chassis is aluminum so it's a lot easier to drill than steel. I filed the sharp edges, the transformer fit the first time!
	Positioning the transformers I used a method called the "headphone trick" to place the transformers. This method reduces hum in the amp by making sure the power transformer doesn't emit energy into the power transformer. Here's the procedure: Tape off all the Power transformer connections except the AC mains (they are usually black) Connect the mains to a power cord and then insulate these and plug in to the wall. Connect the output tranformer secondaries (usually orange brown or blue...any two will work if there is more than one impedance on the OT) to a set of decent headphones. The hum is bassy so decent phones help you hear this. I used alligator clips to connect them temporarily to the phones. It's not important to insulate the primary OT connections since there is no power connected on the OT. With the power on you can move OT around and find the placement with the least amount of hum. The two transformers are usually quieter at 90 degree angles to each other (transformer plates running perpendicular. At a 45 degree angle to each other is good as well. If you aren't sure about what you are doing you can email me. Don't risk your life! Note that the small choke transformer isn't mounted where you see it, it's just there for the photo...
Testing the layout of the controls I decided to make the chassis sit verticle in the cabinet. This way the knobs can be on the top of the cab and easier to see and get to. No revelation here...fender and many others did it this way.	Drilling the tube socket holes I use a stepped bit or "unibit" to drill the large holes for the tube sockets. This takes a while and it's messy with a bunch of sharp metal shavings.
The aluminum is pretty soft but there is still a lot of mess and many burrs to smooth out.	The front panel Ah, the allure of the red fender pilot light! I like using these "Short bat" on off switches from hoffman (see below) . They don't stick out much and seem less clumsy.
Wiring the heater string The heater is the part of the tube that glows orange. This is basically what powers the tube.	Pretty much done with the wiring I ran into a small problem when I was testing the output of the power transformer. I was getting 100 volts more than I expected. The original wurlitzer organ circuit used a tube rectifier and that dropped a lot of that power. Since I'm using silicon diodes there are more volts on tap. I'm going to make a small circuit that will drop these excess volts and give the amp the 460 volts I need.
Cut the control panel insert and test fit chassis Two bolts hold the chassis inside the cabinet. Usually the chassis is about 6 inches tall. Since I was originally going to mount the chassis flat to the top of the cab it's 8". The speaker is a bit close to the tubes.	Front view The pink spots are bondo I used to fill the uneven spots in the face of the amp. I'm using tweed covering so this won't be seen.
Controls I placed the controls so they are reading right when you are facing the front of the amp. I'll paint the control face at some point. Probably a hammertone green color.	Speaker baffle It looks pretty grizzly now but you'll never see it under a coat of black paint and grill cloth. I routed about 1/8" from the face of the baffle. This will keep the grill cloth floating and keep it from buzzing and rattling on the face of the baffle. The thicker edge will also account for the tweed cloth being wrapped over the face of the cabinet. I made a circle in the center of the baffle where it crosses thinking that it will help diffues the sound. I'm not sure I'll keep that since this will be primarily a clean sounding amp.
Worlds ugliest speaker. I may paint this a teal blue/green color like the original Jensen speakers. This one is a Weber ceramic Chicago repro of a Jensen from the 50's	Tweed! The tweed cloth comes in a 64" wide roll. Pretty funny to ship for sure, comes in this huge tube. I'll tackle this job on the weekend.
Installing the Tweed covering

	The inside corners are hard to do. Wne you round the corners the coth tends to split leaving a gap. I ended up with a few places that needed to be fixed. I cut small slivers of tweed and tried top match up the line pattern.
Eventually there will need to be a seam. I measured a straight line and ended up with a not very straight cut. Yay!	Here's my frankenstein style staple job. It held the tweed in place well while the glue set, but left some small dents and holes which I tried to smooth out.

Before "Aging" with amber shellac	After the shellac It gets a bit blochy, but this is hard to do 100% without using spray equipment.
The seam on the top right is a bit unsightly but not too bad. I'm not sure how I would do it different next time. Other than cutting a straight line!	I used yellow wood glue to glue down the tweed cloth. The glue I used was pretty thick which was mostly good although it was hard to spread. It takes quite a bit of glue to get the cloth to stick well. I used more than half a large bottle of glue. I used masking tape and staples to hold down the cloth while it dried. The staples helped but messed up a couple spots but I was able to mash the cloth after it was dry and remove most of the evidence of holes and lines. Small bumps and sharp spots were softly pounded smooth with a hammer. I don't recommend using staples! I practiced on a couple scraps before I did the real thing but still you need to take your time and plan it out. The whole process took several hours and overnight to let the glue set up. Heavily thinned amber Shellac was brushed on to "age" the tweed. I'll probably brush on a couple coats of clear as well to protect the color.
Here's a close up of a corner The corners came out pretty good fot my fist time covering an amp. Can't complain!	Here's another corner This is the bottom panel (top piece shown here) overlaps the side (on right) . The outside corners seem faily easy to do with a little patience.
Inside corners This is where I'm not so sure how to do a better job. When you make the curve it tends to split the cloth and cause a wedge shape gap. I "fixed" these with patches as you can see above. This is a super close up too really see what's going on.	Here's another fudge You can see the botch on this one even more..Yay! From any kind of distance this isn't anything to cry about. With Actual Tolex vinyl you can stretch these inside corners and make it work, I'll have to practice and see If I can pull it off better with tweed. Fender and others did it somehow!
Back panel The back panel is a bit over-sized because I used and 8" chassis run vertical.The tubes hang down to about the middle of the speaker. To protect the tubes and to give it a little style as well as ventilation, I made some cut out windows. I used a forstner bit to make the end shape for each cut out. The I used a jigsaw and a ruler guide to cut the straight lines.	Holes Here are the end holes that will make the shape of the cut-out windows. Since the plywood is so thin and will chip easy I backed the drill bit up with a scrap of plywood. Using masking tape on your wood to be cut will help with chipout on your cut. I did this for the straight lines.
Tweed applied Skipping a little ahead, here is the tweed taped down and drying. Since the back panel is much thinner than the cabinet, the inside curves of the windows come out better and have no visible gapping with the tweed covering. This is the raw tweed shown here.	Back panels finished Here is the finished back. I have given the panels three coats of amber shellac and three coats of clear shellac. I also sprayed the whole cabinet with a fine spay or satin polyurathane to cut down on the glossy finish of the shellac.
Installing the grill cloth When you install the grill cloth you want to line up the patern of the cloth to the edge of your speaker baffle. Staple along the edge of the baffle all the way down the board making sure the grill cloth line you are working from is straight along the edge the baffle. I use 5/16" staples. Staple about every 1/2 to 3/4 inch., don't pull or stretch the cloth as you go along. As long as it's flat to the baffle edge it's fine. When the first side is stapled down you flip it over and dtart on the opposite side. Pull it a little, enough to get it to be flat. You can pull a little and crease it along the edge so it gets flatt along the baffle. Check the pattern against the baffle by sighting down the edge of the baffle. You want the lines of the grill cloth to be straight. Pick a line on the cloth and notice the relation to the baffle. Keep this same distance along the baffle as you staple. Start stapling and keep a little pressure on the cloth so it's not buckled. You don't need to put it tight, we'll get to this later. As long as it's straight and not too floppy it will be fine. NOw continue in the same fashion for the sides. Leave about and inch or more on the corners so you can do the folds.	Two sides stapled. Notice the angle of the staples. You want to paint the baffle face flat black so you don't see the wood through the grill cloth. He oxblood cloth here is very thin and you can see through it quite easily. Here you can see the paint through the back/speaker side of the baffle.
Corners When you are done stapling all four sides you are ready for the corners. Pull the cocrner flat to the baffle. Put a finger on the cloth to keep it from slipping and pull the adjoining corner over the first one at about a 45 degree angle.	When you have made a 45 degree angle and it sits flat, go ahead and put in a staple or two. You can try this a few times until you get it looking right... then staple it down.
After the corner is made and stapled down. Not perfect but who cares? Notice how the lines of the cloth on the right are straight all the way down along the baffle edge. After you have all the coners done it's time to get the cloth tight to the baffle. The grill cloth for fender amps is made from nylon type fibers. It shrinks when you heat it just like army men, drinking straws and plastic spoons etc. You will nedd a space heater or some other lbroad heat source. I used the wood stove that heats out house which is perfect with a 2 foot wide panel and a thick	surface of cast iron.... But any thing like a space heater or a heat gun if you take some care will work. Get it hot but not too hot and not held in the same place too long. Ideally you want to heat the largest area possible until the cloth shrinks a bit. Keep checking it and when it gets tight you can stop. It will shrink until it's cool again so when you think it's about right let it cool down and check it again. The whole shrinking process is fairly easy just make sure you don't get it too hot in one small area or you will melt the cloth!
After the cloth has cooled a minute or two you can cutt off the excess with a razor blade. You don't need to fold it over and staple it. Some times with a fender combo wher yu will be sliding in a chassis you want to fold over and staple the top. his way the cloth doesn't get frayed from the chassis catching the edge pushing over it.	Front of the grill with all sides stapled.
Here's how it looks after everything is done. This is "Oxblood and yellow" grill cloth. You can get just the oxblood brick red color as well, but Iike the lines.	I painted the control panel a green hammertone finish, only the "hammer" part of it didn't work. We decided to stick with it anyway. It has a bit of sparkle to it.
Getting ready for the decals	I used rub on decals available from Antique Electronics or Parts Express. I rubbed these words on to a water slide decal from Small Bear electronics. You rub the letters or words you want onto the decal with a blunt pencil. I cut out each word close to the edge of the letters so there is not much decal around each word.
Put the decal in water and leat it soak for a minute or two. After a bit the decal will slide off the backing and you have a transparant decal . Pick up the decal out of the water and transfer it to the place you want it. Be carefull with the wet decal, they are very easy to ruin. While the decal is wet it's simple to place the word where you want it.	I put the knobs on so I would know exactly where to place the decal. Once the decal is in place the water will evaporate and the decal will be stuck to the surface. If the decal gets wrapped around itself you can put it back in the water to get it straightened out. You may have to tap out bubbles from under the decal. You can gently do this with a Q tip. You can see the decal edges on the top right on thr word treble. These will be less noticeable when you seal the decals.
I had lighlt sanded part of the painted chassis and the "50" decale didn't adhere perfectly. This will go away a bit more when you seal them.	Here are the decals after they have been sealed with a few coats of laquer. It's good to use a spray laquer or poluyurathan and get a few light coats over the decals. I prefer a semi gloss because it hides some of the decal edges and imperfections. Glossy is just too plastic like and reflective.