Attenuation Modules almost complete.

I was able to get 4 attenuation module turret boards created tonight. I then started working on adding the Wire-wound power resistors to those boards. Here's a pic showing the two modules in place. They have to be outside of the amp because they will generate heat. The Module on the left is wired to act as the Medium Level. The one on the right is wired to acts as the quiet level.
They are not finished. I still need to add the wires and the fork terminals to the ends of the wires to make it easy to change them out. I have to call it quits early tonight, I'm traveling to Wilmington to a Local HamFest. I'm hoping to find some tubes there.

Attenuation Modules

Tonight was spent working on the built-in Speaker Attenuation circuitry. Not pictured is a 3 position 4 pole rotary switch. I only needed to use three of the available 4 poles. Here's a diagram that explains how the circuit works. The Switch will have 3 positions. Quiet, Normal/Loud, and Medium. I'm pointed out where I tap into the circuit for my 3 poles.



Here's a diagram that shows how the switch works. It has 3 possible positions. There are 4 wipers that connect the various points together. The Poles are in the center.

I added some stand-offs on the amp. The Amp will have interchangeable Attenuation Modules.
This way any number of power output combinations will be possible.

The Attenuation Modules will have these Power Outputs. This way for example you can configure the amp to have 18.0 watts for large venues, 2.3 watts for practice sessions, and 0.3 watts while playing at home. Later if you decide 0.3 watts is still too loud you can remove that module and replace it with a 0.1 watt module.

• 18.0 watts
• 9.0 watts
• 4.5 watts
• 2.3 watts
• 1.1 watts
• 0.6 watts
• 0.3 watts
• 0.2 watts
• 0.1 watts
  
  

The Quiet Module attach to the three left most terminals. The Medium Module will attach to the three right most terminals. I plan on building the modules tomorrow.

Added the Active Effects Loop Circuitry tonight.

Last night I was able to get a rough prototype of an Active Effects Loop to function properly. It took all day to do it. Initially it didn't work, all I kept hearing was a loud tone shifting noise when I turned on the effects loop. I had to step away from it, and went to dinner. Upon my return I tried a few other things and finally was able to get it to work. Today I spent all day adding the circuit to the amp.

Here's an inside shot showing the added daughterboard with the effects loop stuff on it. I also was able to squeeze in a tube socket for the added 12au7 tube.


Here's the back panel. It will basically be totally removed from the amp until needed.
You then pull the Send Knob out. This adds the effect loop circuitry to the amp.
With the Send and Return volume knobs, you can then vary the input to the effects and vary the output from the effects back into the amp. I tested using a patch cord and It actually boosted the preamp output a little more than stock. It also gave the amp a little bit more crunch at max volume which was an unexpected side benefit. I've very happy with the end result as I was reading how a passive (with out an extra tube) effects loop cause a significant reduction in output. With the addition of another preamp tube we get the benefits of an effects loop without any loss in headroom.

Here's the 3 12ax7 preamp tubes with the added 12au7 Active Effects loop tube.

Getting into NOS Tubes Big Time!

This past weekend I had to go to the coast to check on the boat. On the way back I stopped at a small town HAMFEST (HAM Radio Festival/swap meet). I scored some NOS (New Old Stock) tubes from a guy who picks them up at estate sales and from some friends. Another guy had these NOS Capacitors which will be for future amp projects.

I was able to get the tubes for $1 each and the rest for $2, total spent $10.00.

The tubes are (6) NOS American Blackplate RCA's and (2) Raytheon 12au7's. Not a bad use of a half hour of time out of my weekend.

Also during the HAMFEST I talked to another guy who runs a Salvage business. I takes in equipment from all over and salvages all of the parts from said equipment. He invited me to his warehouse where he said there are bins and bins of vacuum tubes to be had. By bin I'm referring to the 4' x 4' x 4' pallet bin variety. Oh Boy, it looks like my dream of treasure hunting off the coast of North Carolina might actually involve sifting through a bin of vacuum tubes on an upcoming Saturday. Who knew!

To go about selling any tubes that I find I've been reading up on how tubes were tested in the past. I found a great web site devoted to Tube Testers http://www.tone-lizard.com/Tube_Testers.html. After absorbing this information I was able to snag a nice Hickok 600A Mutual Conductance Tube Tester.

It also turns out there there is one of the foremost authorities on Tube Tester Repair an Calibration nearby in Greensboro NC. My Tester was recently calibrated there.

Here's nice a pic of a Hickok 600a that I found on the web, click to zoom in.

You basically look up your tube on the roll chart, it tells you what to set the dials at then you press some buttons and turn some knobs. This is right in line with my Geek tendencies so i think it will make a nice addition to my tool collection.

Today Raleigh had their HAMFEST. Which is the largest in Raleigh and only once a year. The knowledge of the vendors was a little better as they weren't giving the stuff away. But I was able to sift though the countless boxes of old tubes to SCORE some sweet tasty little gems.

From left to right. A Raytheon EZ81 NOS Rectifier. That one is super rare but I'll put that in my friends Amp #2. The white boxes are NOS GE Blackplate 12au7's that are in the most pristine condition. Like new. Followed by an assortment of NOS American pre-amp tubes. The right most are the gems I found in a bin of about 200 unboxed tubes. I found 3, yes 3 Mullards!

What a SCORE!

The guy's jaw about dropped as he didn't know they were in there. I was able to walk away with them for $18 each. The rest of the tubes were sub $10. I'll have that tube tester paid for in about a week at this rate.

Here are the 2 mullards, I forgot one was still in the bag (not pictured) and a nice backplate

pre-amp NOS tube to the left of them.

On the Amp front I was able to change out the Tremolo Pot on AMP #2 from a 2meg to a 3meg. Doing so gives it a wider range of tremolo speed to choose from. After lunch I plan on diving into seeing If my design for the Active Tube based Effects Loop is going to work with this type of amp architecture.

Amp Head covering complete.

Tonight I came home from work and brushed on the DAP low VOC contact cement. Here's a pic of the Tolex (Vinyl) with 2 coats of contact cement applied. I let it dry about 1.5 hours and then applied a 2nd coat to make sure I didn't miss any spots.

I found that the Tolex (Vinyl) dried about 1/2 as slow as the wood cabinet. So I ended up having 3 coats on the head cabinet and 2 on the Tolex. Here's the head hanging in my garage.
The next step I used some wax paper to lay under the amp head and also on top. I then put the Tolex on top on the wax paper. The wax paper kept the two surfaces separated, until I was ready. I added some tape and drew reference marks at the middle (lengthwise) of the Tolex sheet. This is so that the seam on the bottom of the amp was somewhat in the middle.

I then measured the overhang on each side, at the front of the amp. This was to make sure that it wasn't on crooked. I needed it to be straight because I only had about 1/2" overlap on the bottom seam, so I was cutting it close.

Here is the bottom of the amp. This is the easy part. You just overlay the Tolex and using a sharp knife and a straight edge I cut down the middle of the two pieces where they overlapped each other. (2 thick). After I finished the cut you pull of the 2 scraps and you are left with a perfect seam where both pieces lie flat (no overlap), and butted up against each other.

Here I'm securing the inside of the head. At the bottom of the picture is the top of the head. (upside down)

Here's a corner detail, of the back side of the amp head. I read about applying Tolex, they say after your 100'th amp you get the hang of it. I got the hang of it during this one, but the next one will be better because I realized where I could improve the process. Especially when cutting corners.

Here is the completed Amp Head Cabinet. This is a view from the front, I'll most likely have a wire mesh under that slot (vent).

Here's the top of the head

A view from the other side.

This is a view of the back of the Amp Head.

Finally a view from the back of the Amp Head. I set the front of the cabinet face down on my cutting mat. I envision that the amp face plate will rest against the amp face boards.

Started to put the Tolex on

Prior to sending my order off to BNP Laser Engraving. http://www.bnplasers.com I had printed out the faceplate on some transparency film to make sure that all of my holes would match up. I had to remove all of the components and pull them inside the chassis, to make sure these measurements were right on. I was also able to finish rewiring Amp #2 this weekend. I must say that I was starting to get worried. After re-wiring it it had a nasty hum (60 cycle). I tried adding some shielded wires and even rerouted some wiring. I was stumped. I then realized that you can't have my el-cheapo guitar right next to the amp while you are messing with it. My guitar's pickups were picking up the magnetic fields from the power transformer. Duh! A hard lesson to learn. As a result I'm really happy with the wiring on the inside. Moving away from the amp about 2 feet, it's about dead silent, no hum!


This week I've been reading all about how to apply Tolex to the cabinets. I even had some scrap vinyl laying around that I was practicing with. This helped and If I had started doing it, it wouldn't have turned out very good. Tonight I started with adding Tolex to the Vent slot in the top of the Amp Head Cabinet. My strategy is to lay down a thin strip around the slot as a base layer so that when I have to cut the top covering around the holes, no wood will be exposed around the slot.
Here's the Red Tolex, that I got from Mojo Music Supply. The rotary cutter makes it easy.

After reading about contact cement, I went with DAP low VOC. I've used the regular DAP stuff and I must say that stuff takes years off your life. It's very potent. This stuff (green can) is water based which also makes cleanup a lot easier. The downside is that it takes longer to dry. I found it took about 1.5 hours to dry. Next time I'm going to do two thinner coats to speed the drying process up a bit.

Here a top view of the vent slot in the top of the head cabinet.

Here's an inside pic of the Tolex that I'm adding to the slot as a base layer. Yesterday I spray painted the inside flat back.

Here's a top view of that strip, added to the slot.

And a shot from inside. This low VOC contact cement is a little easier to work with. It allows you to move the Tolex around a little instead of grabbing it and not letting go, like the regular contact cement would do.

I'm letting this dry overnight.

Backing up a bit.

I ran into an issue with Amp #2 when I went to plug the tubes into those nice gold bottom mount sockets. It was extremely hard to get the tubes into the sockets and harder yet to get them back out. I'm going back to the regular ones and have those on order. They allow easy tube changes without any risk of bending pins. Since I'm removing those sockets I also decided to do some house cleaning and will shorten each wire to its minimum length. Doing so will reduce noise in the circuitry. I will then know what that length each wire should be so I'll be able to use this recipe in the future amps. This will make it a lot easier to wire up. I also found another builder's amp and his heater wires where a work of art. So I took his lead and created a new set of heater wires that are much prettier than the previous ones.

New heater wire harness

My friend requested a Send and Return effects loop, so I needed to re-arrange some items on the back panel. I also had to add another hole. In the end I think it was for the best because now things will be laid out in a nice orderly fashion. But there isn't any more room for holes, so that's about it on the bells and whistles for this amp.


Here's Mizzen doing quality inspection. The ole sniff test.

I brought the two pieces I have done back home so I can start practicing the art of laying out, cutting and securing the Tolex to the cabinet. This is my first attempt so I plan on using some other materials to figure out how to do the corners and such correctly. I have some vinyl laying around so I might practice with that first to get the hang of it. The last thing you want to do is have the contact cement curing away while you figure all of this out.

Amp # 2 Works!

I was able to get Amp #2 working tonight. At first there was no sound, I only had the guitar leaning against the table. I then noticed the guitar's volume knob was at zero, DUH!
Amp #2 works. I'll still need to add some more stuff to it. The preamp circuit, the attenuation circuits and clean up the wiring a bit, but it's coming along nicely.

On the faceplate front I have the face plates mocked up in PowerPoint. I'll be submitting them in a few days.

No Mas! No Mas!

I've explored countless avenues and I'm giving up on making my own faceplates. I'm going to contract Amplates (www.amplates.com) to make them. Last night and tonight I'm been carefully measuring the chassis and drawing up the specs for them to start their process.

Tonight after I finished measuring the chassis for a 2nd. time to make sure I had valid measurements I started hooking up the Big Iron. No not a Harley Davidson, but rather the Heyboer Transformers made to Graydon's (www.gdsamps.com) Vintage 18 Watt Specifications and manufactured by Heyboer in Flint Michigan.

Pictured here is the Power Transformer. I'm hooking of the rear components because I need to test things out and validate that my resistor choices for the attenuation levels are going to work out. Later when the back face plate comes I'll only have to desolder the fuse, and the power cord receptacle to install the rear plate.


Here's the output transformer. That might go in tomorrow night, but I need to pick up some rubber grommets to protect the wires passing trough the chassis holes.

Turn it down please!

Tonight I started working on the Attenuation for Amp #2. My friend will want to practice at home and most likely play in some smaller venues. I'm building into the amp the ability to reduce the volume at the speaker, but hopefully not affect the quality of the sound too much. This will allow the amp to be cranked up to get the desired distortion, all the while enjoying a volume level at the speaker that is neighbor friendly. There is also the possible situation of playing in a smaller venue where a full 18 watts is way too much power. Besides having the ability to go to eleven this amp will also be able to go to a polite eleven.

I found this schematic along with an excel sheet that calculates the values for the various levels of attenuation given a speaker impedance value.
(Link to the site with the excel sheet http://www.wohlgemuth.de/board/bridged_att_calculation.xls)


Luckily I had some turret board material and some turrets on hand. This set allows for two levels of attenuation. These these values will produce 9db or about 2.3 watts of output. The other level is for at home use with 20db or about 0.2 watts of output. I'll be able to tweak these values just by changing the resistor values out.
There will be an Attenuation Switch on the back of the amp that will function like this:

• Up - 2.3 watts
• Middle - Off (Removes it from the circuit)
• Down - 0.2 watts

Mouser (www.mouser.com) didn't stock a 15watt 30 Ohm resistor, so I went to the next higher wattage rating to obtain the needed Ohm value. I'll most likely fashion a metal screen to protect and hide these resitors but still allow them to radiate the 18+ watts of heat at full tilt. Mind you that since we are talking waves, that roughly only .7 of the 18 watts is required.

Speaker Cabinet #1 for Amp #2

Yesterday I made two new baffles for the second attempt at cutting out the speaker holes. Here is a picture with my template nailed to the backside of the baffle. I'm using a flush trim bit in my router, the bearing will ride against my template making for a nice round cutout.


This time I cut a smaller circle using my jig saw to allow for any slop in the cutout. I also didn't have to try to make a perfect circle. Which made it a lot quicker and easier to cut. You can see that I have a good 1/4" of wood that I'll need to remove with the router bit.

Here's the hole after removing all of the extra wood.

Finally, two baffles I can be proud of.

Here I'm lining up the speaker with the hole to make sure it is centered. From the backside I then used a center punch to mark the holes. Carefully drilled almost all the way through the baffle and installed 4 Wood screw/machine screw studs into the back of the baffle.

This is the backside of the baffle. I used my speaker for a guide.

Here is the bottom plate for Speaker Cabinet #1. I had to route the baffle Dado (Left to right, at the bottom of the pic). And a rear Dado for some gussets and nailers for the rear panels, that are removable. I'm using Tightbond III waterproof glue for these cabinets.

I had to work quick to get the sides and the baffle in place. I didn't have time to take pics on each placement. The top went on next (to the right in the background)

Here's the cabinet all glued up. I used some 18ga. brads, using my air nailer to clamp everything in place and to provide some more strength. Through the cutout you can see the rear gussets. I'm also going to add strips in the dado to act as a base for the rear panels to screw into and to strengthen the rear part of the box a little more. These should make a good seat, with a chair height of 20 inches they should be about perfect to sit on.

It was getting late, but I was able to make the front trim. This will add some width to the front of the cabinet and make it look thicker from the front.

Another pic of the nearly completed Cabinet #1. Cabinet #2 will go together in a few minutes. I figure I only have about 2-3 more hours of work get these and the head ready for covering.

This is the backside of #1.