Weber AB200 Bass Amplifier Build

[MarkE]

10/20/09 - Humble Beginnings

I am going to do a detailed photo build of this amp complete with thoughts and notes in the hope that it will aid anyone else who builds this fine amp and help them to avoid any surprises or mistakes I'm bound to make. I really am in no hurry to complete this. I'm in it basically for the build. When that is complete, to me it is like the ending of a good movie. I always want more. Given this, I can really dig in and show some detail. I hope that someone finds it helpful, but be forewarned, I tend to babble a bit. :)

The amp kit has been here for a few days now. I plan to build this amp basically stock. I did notice that there is an extra tube socket which will be covered with a plate, and also two extra holes in the front panel for two more pots. I may decide to add an overdrive stage later or make some other use of this.
I also plan to light up the inside of the head cab with CCFT lighting. I'm still considering colors. It will most likely be green or ultra-violet. I will need to build a small 12VDC power supply into the chassis to power the light's inverter. I'll have to look around for a small 12VAC transformer. I will most likely build the supply on a terminal strip.

Other than that, I'm good to go.


First, I started test fitting everything. Quite a bit of planning goes into a project like this, and if there is one thing I have learned it is to test fit everything several times before actually cranking up the soldering iron.

The chassis was real nice. Nothing to be deburred or enlarged except for the hole for the pilot lamp which was only slightly. Two other things I needed to do were....

Two of the fiber boards mount on nylon standoffs which are attached from the top of the chassis with a round head screw. Three of those screws ended up under transformers. Two of them under the power transformer and the other on directly under the transformer used in the phase inverter section. For that last one I decided to countersink the screw so that the transformer will lay down flat on the chassis. I swapped out the round head for a flat head. This took only a few minutes. As for the other two, I wont be certain as to what to do with them until I get the PT in place. I could always counter sink those too if necessary.

I also tried test fitting the chassis in the head cab and it didn't fit. I needed to take a razor saw and make four small cuts on the wooden vertical supports. Everything fits correctly now. I will probably repaint the interior of the head cabinet as I am going the light up the inside of the amp with CCFT lighting.

Here are a few shots of the chassis during the final test fit. I need only drill a couple of holes for some terminal strips once I know where I want to place them.

http://www.thehawkstudio.com/picts/ab200/IMG_0001.JPG

The rear panel on this thing is really sexy. There are six individual bias adjustments, one for each tube. There is also an LCD volt meter which will read the cathode current on each tube as well as plate voltage. There is a rotary switch to switch between the tubes. The slide switch selects either cathode current or plate voltage and also controls decimal point placement on the meter. The voltage divider for the plate voltage was very smartly included on one of the fiber boards. I love that Ted chose to provide several speaker jacks for various cab setups instead of using a simple rotary. I like this much better.

http://www.thehawkstudio.com/picts/ab200/IMG_0005.JPG

http://www.thehawkstudio.com/picts/ab200/IMG_0008.JPG

http://www.thehawkstudio.com/picts/ab200/IMG_0010.JPG

I decided to leave the two massive transformers off the build for now. It will be a lot easier to maneuver the chassis without them. I will probably start with the heater buses and wiring the back panel first. The combination of the LCD meter, slide switch, rotary switch and six bias pots should keep me busy in that section for a while.

[MarkE]

BACK PANEL BIAS WIRING

I started by wiring the back panel. I thought it might be a good idea to do this before things get crowded.

The heater runs and plate rails for the 6 KT88s are also in place along with a terminal strip. For the heater runs I followed Granger's lead and used untwisted solid wire. I didnt have any teflon sleeving so I used some 18 ga bare wire and covered it with teflon insulation stripped from some #16 stranded wire. The plate rails are 16 ga stranded (blue-white).
The bias monitor resistors have also been installed and wired to the rotary switch and meter.

http://www.thehawkstudio.com/picts/ab200/102309-IMG_0007.JPG

The slide switch selects between cathode current and plate voltage. I elected to remove the decimal point (always on) jumper on the display and wire it to the unused side of the slide switch. Now the decimal point will be disabled when plate voltage is selected. I included this picture in case another builder has trouble figuring out the jumper location and the associated wiring. Before beginning this project I assembled and tested the LCD meter to figure out the details. The piggy-back board is a 120V to 12DVC power supply. The voltage actually comes in way high....somewhere around 30VDC. I did notice some modifications made to the meter so I'm guessing that it has been modified for this. It normally runs from 7 to 12VDC. I hope its right. The meter seemed to run well for a long period of time during the bench test. I noticed that there is a small trimmer pot on the meter which I'm guessing is used to calibrate its reference voltage. I will test its calibration at a later time. I need to dig up an accurate low level voltage for the test. The meter is setup for a 0-200mv input.



http://www.thehawkstudio.com/picts/ab200/102309-IMG_0002.JPG

http://www.thehawkstudio.com/picts/ab200/102309-IMG_0012.JPG

Weber includes a fan kit complete with a small PCB and slide switch which acts as a voltage doubler and two position speed control. It can be seen mounted in the upper right corner. The slide switch is accessible from the top of the chassis and is driven from the filament winding. I really like this configuration. I plan to pass the fan wires along with the CCFT lighting power through the grommet in the upper right corner and terminate them on some molex connectors to allow easy chassis removal.

http://www.thehawkstudio.com/picts/ab200/102309-IMG_0003.JPG

[MarkE]

I decided to stop and build the billboard. I call it that because of the way it is mounted in the amp. I made a few minor changes so a few of the flying wires exit the bottom of the board instead of the top.

Here it is

http://www.thehawkstudio.com/picts/ab200/102709-IMG_0002.JPG

http://www.thehawkstudio.com/picts/ab200/102709-IMG_0005.JPG

http://www.thehawkstudio.com/picts/ab200/102709-IMG_0007.JPG

Nothing to report. All went smoothly. I will mount this board in the chassis next.

[MarkE]

PREAMP BOARD / CAP CAN WIRING

I started work on the preamp board. Here are some before and after shots.


http://www.thehawkstudio.com/picts/ab200/102809-IMG_0005.JPG

http://www.thehawkstudio.com/picts/ab200/102809-IMG_0009.JPG


http://www.thehawkstudio.com/picts/ab200/102809-IMG_0013.JPG


Here are both boards mounted in the chassis. I have plenty of wiring coming up!

http://www.thehawkstudio.com/picts/ab200/102809-IMG_0014.JPG


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Here is how I chose to wire the cap cans.

http://www.thehawkstudio.com/picts/ab200/102809-IMG_0022.JPG


The layout seems a bit odd me.The run comes from the standby switch/power supply board all the way full length across the chassis diagonally to the cap cans and then back, and then A supply runs again across the chassis to the output board. Ted has an important note on the site to follow the layout so that is what I will do.

[MarkE]

OUTPUT BOARD WIRING
Nothing to mention here. Im just providing a few pictures. This should nearly complete the wiring on the back panel.


http://www.thehawkstudio.com/picts/ab200/103109-IMG_0014.JPG

http://www.thehawkstudio.com/picts/ab200/103109-IMG_0016.JPG

[MarkE]

POWER TRANSFORMER MOUNTING AND ASSOCIATED WIRING

My gawd this thing is heavy! One thing I should note....as indicated on the layout drawing you should mount the stand-offs for the power supply board BEFORE mounting the transformer as two of the three stand-offs will be located under the transformer. This brings up another small issue. If you use the standoff screws provided they will interfere with the transformer. I elected to switch to flat head screws and countersink the heads slightly so that there are flush with the top of the chassis. This is easy. just use a larger diameter drill bit and enlarge the top of the holes so that they take on the "cone" shape of the screw. Do not drill all the way through. I know there are better tools for doing this but this works well in a pinch.

I elected to terminate all unused PT lines to a long terminal strip. It also provided a convenient place to pick off switched/fused line voltage for the PT, 12VAC transformer and LCD meter described later.

http://www.thehawkstudio.com/picts/ab200/103109-IMG_0007.JPG

http://www.thehawkstudio.com/picts/ab200/103109-IMG_0009.JPG


The heater wires from the PT are huge. I had considerable trouble in both taking the live leads (the greens) to a terminal strip and also getting the center tap wire (yellow) secured to a terminal lug where it is bolted to the chassis. For the CT, I opened the back end of a standard terminal lug, pre tinned the yellow wire and crimped it in the best I could. I then soldered the heck out of it with a 100W soldering gun. I have a nice secure connection now.

For the heater wiring, I decided to star off a 2 lug terminal strip. From that terminal strip there will be star runs to a) the pilot light, which will continue on to the preamp tubes, b) the fan motor board, c) the EL34 and the six output tubes.
Given the number of connections and the diameter of the green wires from the PT, it turns into a bit of a nightmare. It looks a little sloppy but the connections are very secure and should hold up well.

http://www.thehawkstudio.com/picts/ab200/103109-IMG_0006.JPG


I installed a 12VDC supply for the CCFT lighting inside the chassis. It consists of a 12VAC transformer along with a half wave rectifier (1 diode and a 1000uf/50V capacitor). The diode and cap are built on two unused lugs on the PT's terminal strip. This 12VDC and the red/black for the fan needed to be routed to the top of the chassis. I decided to use a 4 pin standard molex connector (same as used in standard computer power supply connections) through the grommet to the top of the chassis. This way I can simply unplug both when i need to remove the chassis from the cab. The inverter for the CCFT lighting will be mounted in the cab along the top or side wall out of sight. I thought it might be a good idea to keep the inverter out of the chassis and I also didnt have enough room for it.

http://www.thehawkstudio.com/picts/ab200/103109-IMG_0022.JPG

http://www.thehawkstudio.com/picts/ab200/103109-IMG_0004.JPG



The 12VAC transformer is powered by the switched/fused line voltage. I bench tested the half wave power supply with the inverter and lights beforehand. It all worked well. It drives two 12" green CCFT tubes. I also have two black light tubes but they weren't terribly bright but looked really cool. I will experiment with them at a later time. Its hard to tell how they will look until I get everything buttoned up with the two black mesh screens.

I also ran a set of leads from the 12VAC transformer primary to the 120VAC input on the LCD meter. This all tied together into a nice neat package.

When I completed all of this I did a quick power-up test. It all works.

[MarkE]

POWER SUPPLY BOARD

After completing most of the power wiring in the chassis it was time to build the power supply board. It should be noted that the eyelet board supplied in the kit is different than the one shown on the layout. No biggie, just examine it and plan it properly. I elected to place the parts on, what would normally be considered, the back of the board. This way the orientation of the parts is better for the upcoming wiring.

This is how I elected to do it:

http://www.thehawkstudio.com/picts/ab200/110109-IMG_0004.JPG


http://www.thehawkstudio.com/picts/ab200/110109-IMG_0008.JPG


http://www.thehawkstudio.com/picts/ab200/110109-IMG_0013.JPG

When built like this, the main secondary from the power transformer (red leads) will connect to the rectifier diodes in the upper left hand corner which is located just above their entry to the chassis. Also, the take offs for the choke, A, B, C and D supply are located on the bottom which is a better location.

I elected to bridge each diode with a .01 1000V capacitor to help smooth their switching and hopefully give them longer life and reliability. Other than that, the board was built stock.

[MarkE]

Preamp Board - Front panel

In preparation for installing the preamp board I did some preliminary wiring on the front panel controls, built up the mid shift rotary switch, ran a ground bus and attached flying wires to the board. Here are two shots just before installation.

http://www.thehawkstudio.com/picts/ab200/110609-IMG_0001.JPG

http://www.thehawkstudio.com/picts/ab200/110609-IMG_0002.JPG

From here I am going to make a hard run to the finish line and get all of the remaining wiring finished. I have actually completed that after taking these photos. I should have photos up sometime today.

[MarkE]

Build Complete - First Full Power Up

<Pictures to follow shortly>

With all of the basic wiring now completed, I decided to power up. Using a light bulb limiter, I brought up the amp without the tubes in it. All seems well. One thing I should note...without tubes the C supply will float up past 500V and stress the filter cap rated for only 450. I noticed it happening when I heard the familiar "cap crackle". I'm not sure if I damaged it or not but I'm sure it does it absolutely no good. I will go back later and change it out.

After making a few measurements, shutting it down and bleeding it out I installed all of the tubes. I setup the meter and scope and fired it up again. All of the heaters lit normally and there was some 60hz hum in the speaker with all the volumes turned down. I made a quick survey of all the vital signs and all appeared normal. I then focused on setting up a preliminary bias for the output tubes. As a start, I set them all for 50ma. Plate voltage came in around 540VDC. With the LCD meter and rotary switch, setting up bias is quick and easy. It only took a minute. There is some interaction between the controls but much less than I expected. You need to make a few passes to get them all on target. Even with that it was ridiculously easy. I can see that I'm going to love this amp. This meter setup will allow you to always keep your amp in tip top shape and also help troubleshoot dead or dying tubes, and to keep a "basic" eye on your power system.
To minimize interaction between the controls, I would recommend bringing up the bias for all six tubes in 10ma segments when you first set it.

http://www.thehawkstudio.com/picts/ab200/110709-IMG_0066.JPG


I then plugged in my Fender Jazz Bass and raised the volume a little. I played a few lines and all seems normal.

Here are some minor issues I encountered:

When I get the volume up past around 5 it started into a high pitched oscillation. Reversing the leads from the driver transformer into the billboard solved that. I can now dime the amp with treble and presence all the way up without ill effect.

I am getting some hash. I traced it (I think) to the wire running from the volume control's wiper to pin 7 of V1. This wire is really hard to get to. I will have to remove the mid shift rotary to get to it. I plan to try a shielded wire there.

I am getting a little 60hz hum which I will work on later.

For now, all seems okay and the amp sounds great. I quick connected the fan and CCFT lighting to the molex connector installed earlier and then ran the amp for about 30 minutes. All seems good. This thing builds up quite a bit of heat just running on the bench so be aware of that. The front face plate in the area with no controls passing through it actually started to buckle. I will go back and nail it down with some glue.
Other than that all appears to be normal. I will continue working on tweaking it out before installing it in the cab. The chassis is so heavy I don't want to have to install it repeatedly in the cab. My back can only take so much abuse.

Here are the two CCFT lighting tubes along with the inverter that I will use in the cab. This is available from All Electronics in a variety of colors fairly cheaply. The inverter runs on 12VDC and eats about 650ma.

http://www.thehawkstudio.com/picts/ab200/110709-IMG_0061.JPG

Full chassis photos are up next.

[MarkE]

COMPLETED CHASSIS PHOTOS

Okay, here is a complete look around inside the chassis. There may be some minor changes (indicated above) but this should be it.

http://www.thehawkstudio.com/picts/ab200/110709-IMG_0004.JPG


http://www.thehawkstudio.com/picts/ab200/110709-IMG_0005.JPG


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http://www.thehawkstudio.com/picts/ab200/110709-IMG_0073.JPG

I will continue on tweaking but cab assembly is next. Stay tuned.

[MarkE]

11/08/09 - WRAPPING IT UP

Okay, all done. Today I installed the lighting, tweaked the bias and took it for a spin. I did a one hour test run through my utility speakers (2 x 8 ohm 15" w/horns).

The first shot shows the CCFT lighting installation.

http://www.thehawkstudio.com/picts/ab200/110809-IMG_0005.JPG


http://www.thehawkstudio.com/picts/ab200/110809-IMG_0016.JPG


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http://www.thehawkstudio.com/picts/ab200/110809-IMG_0052.JPG


http://www.thehawkstudio.com/picts/ab200/110809-IMG_0061.JPG

I still have a few minor tweaks so I have to pull it apart one more time. It sounds amazing. I will try to shoot a youtube vid of this amp in action. With the mid shift control it really does get a full range of sounds.

Thanks for watching. If anyone has any questions about building this amplifier, please feel free to contact me.

MarkE

[McGinnis]

Looks Sweet!!!!
I need a bass!!

[babayaga]

I recognise this amp from a certain video full of pomp, green circumstance, and a few helicopter shots! Great stuff!! Ha!!

[MarkE]

Yeah...thats the one! I couldnt resist using it :)
This was a tough project....especially during troubleshooting. Everything had to be "just so", but once I got it I have to consider it the best bass amp I've ever played through. Heck...I should have bought an Ampeg SVT back in the early years.

Mark