Monthly Archives: April 2010

Tubescreamer clone

While browsing the Hoffman Forum I clicked on a new member’s profile link, and it took me to this product page of a PCB for a Tubescreamer clone. I have been wanting to build one of these for a while now, and once I finish my P1eX, I’m going to do just that. So here’s the plan:

I can do a funky paint job (or even a boring one..who cares) without too much difficulty, so this looks like a pretty cheap project at $37. Talk about bang-for-buck!

PS Originally I typed TUB-screamer. I think I prefer that name 🙂

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Beginning assembly of P1eX

The quiet before the storm. Note the pile of baggies from Tube Depot...most handy!

So the previous week, in an effort to have everything ready for assembly, I order the remaining parts. This amounted to all the resistors, capacitors and diodes that make up the circuits on the board. Finally, I needed tubes of course. I ordered from these folks:

  • Tube Depot – They have all kinds of manufacturers in stock, and the shipping is fast and high quality. Each component arrived in its own ziplock baggie with a decent label. Very cool for a newbie like me.
  • Eurotubes – I decided to go for a 6V6 in the output section and Eurotubes was the only place I could get a JJ 6V6 in a one lot. Every other place wanted to sell only pairs, and their prices were high anyway. Naturally this site is a big proponent of JJ, but others online have sung their praises. If these work out I may retube my 2204 with a set from these guys.

Before starting I laid everything out on my dining room table, and made sure I had plenty of light. To ensure accuracy I had both the schematic and the layout diagram available. And so as to maintain diplomatic relations with my significant other (i.e. not burn the table), I used a print out of the AX84 theory document for the P1eX as an “earth friendly soldering station”. Fitting, really.

So, now it was time to begin attaching stuff to the turrets. I started with the wires that go under the board as this made total sense (and the guide told me to). I had already drilled holes next to the appropriate turrets so that I could keep the solder joints above the board, but still route the wire underneath. Apart from the build guide recommending this, I was also keen to never have to remove the board once built as having previously repaired my Marshall 2204 it was a royal pain to have to remove the PCB to de-solder components.

Under-board wire

A wire routed underneath the board surfacing to attach to the turret

Bare turrets

Bare turrets with adjacent holes waiting for wires. The larger hole is for the chassis stand-off.

After all these were in place, and making sure I had marked these as ‘done’ with a hi-lighter on the layout diagram, I started on the right hand side of the board with the power supply diodes. As I worked my way through the layout I was troubled by a few things:

  • Progress

    Progress. The first few joints drank solder like it was going out of fashion.

    Is there a “rule of thumb” to help decide where/how to solder a component? i.e. do you put caps/resistors/diodes inside the turret, and wrap wires around the turret? Or is it the other way round? I did both as I saw fit, but it’s not particularly neat and tidy.

  • Do you wrap as many components around each turret all at once and then apply solder? Or do you do them one by one? Again, I did both, but the latter meant components were heated multiple times, therefore went under more thermal stress.
  • How do you stop the turret itself wicking all the solder away? Early on I found that if the turret got too hot it would wick solder until you filled it up. And in fact when I turned the board over there were quite a few lumps of solder that had fallen through and pooled on the paper I was using as an ad hoc insulating surface. I think this is down to technique. Later on I got better at keeping the heat on the parts as little as possible which meant I could minimize the amount of solder. This must’ve been due to the lower part of the turret remaining below solder melting temperature, thus no wicking.
  • The ground bus along the top of the board cried out for a single wire to be connected from turret to turret. I decided to use my 20 AWG solid core wire (as I had been using that all along) but it didn’t come out looking especially nice. I’ll do it differently next time…perhaps thinner wire?
99% done

The board with a few missing/incorrect bits. Note the wiggly copper ground bus along the top

Along the way I realized I had screwed up my order to Tube Depot. A missing component here, a slightly-wrong component there etc. Never mind, I can go to Radio Shack during the week as it is only 5 minutes walk from the office, whereas from home it’s a 20 minute drive. Normally this would’ve irritated me, but I still had plenty of interesting stuff to do after soldering all the remaining components and wires.

So time to put the board aside and do some work on the chassis. The day before I had sprayed the amp’s chassis with a black ‘Rustoleum’ hammered-finish paint. It came out surprisingly well seeing as I was rushing (over excited) and humidity and temperature weren’t ideal. 24 hours later the paint was dry so I started adding pots and lights etc. This part was easy as I had already ‘dry fitted’ the parts a couple of weeks ago. I definitely did not want to have to drill anything out again once assembly had begun.

Once I had the transformers in place I decided to proceed with the filament wiring. I had some green and black solid core wire, so I used that to make the connections. Twisting the green wires from the power transformer wasn’t so easy as they are stranded. Stranded wire doesn’t seem to like keeping its form once twisted. We’ve all experienced a neatly coiled wire that transforms into a tangle once you let go of it. Luckily though the run from the PT to the pilot light is short. Twisting the black/green solid core was a breeze in comparison and I soon had plenty of wire to connect the pilot light to the output tube and the first preamp tube.

Filament/heater wiring

Green wires from the PT, to the pilot light, then my green/black wires going to the tube sockets.

Filament wiring at the sockets

Filament wiring at the output tube socket.

Overall I was very pleased with the weekend’s progress. It’s really starting to look like an amp now! I’ll have the missing/wrong components in order this week, and I might even be able to get some sound out of it within a couple of weeks, time allowing.

PT/OT

The PT and OT in their new homes. You can see the full effect of the hammered black paint.

Chassis so far

Chassis so far. I must order some proper knobs for it.

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Circuit board preparation

Bare board waiting for holes

Here's the bare board laying on the scaled drawing. The sizes match up quite well.

This weekend’s fun was all about getting the circuit board ready for population with components. Secondly I had to make sure it fit in the chassis correctly as that was the only thing holding me back from painting the chassis.

Drilling holes using the fence

Drilling holes using the fence made for fast and accurate work.

My first step was to make sure the drill plan for the board was correct. I ended up using the main layout drawing as my template as it was closer to the size I wanted. I ended up getting it copied and scaled by 114% at Kinkos so that it was approximately 12 inches by 3 inches. I cut out the template with a craft knife and used masking tape to stick it to the board. You can see from the template that there are 4 distinct rows of holes (not including a few random holes for wires or the ones to secure it to the chassis). This meant I was able to use the fence that came with my drill press to keep these lines straight. Drilling with a brand new 3/32nd” bit was quick and easy with this material. I made sure the drill speed was nice and high (about 3000 rpm) and used slow pressure. It only took about 10 minutes to drill all the holes. Where I new the holes were for mounting to the chassis, I used a 7/16th” bit.

The middle hole

The middle hole drilled with the board snugly attached to the chassis (temporarily)

Once drilling was complete I needed to make sure it fit in the chassis’s existing holes. I knew there might be an issue as I had used a scaled drawing, and sure enough when one pair of holes were lined up the other two were off by about 1/8th of an inch. I used a spherical grind tool with my Dremel to enlarge the holes in the circuit board. It took less than 30 seconds to make everything fit neatly. With the board attached to the chassis with 4 screws and the standoffs, I used the existing ‘middle’ hole in the chassis to drill all the way through into the board.

Staking tool

The staking tool setup in the drill chuck. The vice bolted neatly onto the bed of the drill press for added stability.

Now the time had come for “staking the turrets” (such a medieval term). All this required was for me to install the staking tool according to the instructions, place a turret in the tool, place the board over the turret using a free hole and then pull firmly down on the drill press. This action squeezes the conical tool into the bottom of the turret causing it to flare out. This causes it to grip the board firmly. I had initially tried to do this by loading up 10 or so turrets into free holes and then flaring them, but they’d always fall out so any time savings I made were lost by searching the bench for dropped turrets. Once I got quick at loading turrets into the bottom part of the tool, and then placing the board over the turret I became quite adept. Total time for all turrets was about 10 minutes.

More staking of turrets

More staking of turrets

All board material, turrets and the staking tool were purchased at Hoffman Amplifiers.

Next steps: paint the chassis (now I have all the holes finished and soldering components onto the board. (must remember to order said components).

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Fitting of parts

These two recent weekends gave me a few hours to keep moving forward on the chassis. I had done the bulk of the drilling according to the drill chart and was ready to dry-fit some parts to make sure I was on the right track. My intention is to paint the chassis, so I have to know that I’m not going to drill any more holes prior to finishing.

Inside the chassis

Inside the chassis

The parts themselves I bought from 4 sources:

  • Hoffman – great for high quality parts oriented towards scratch building and Fender amp repair/modification. Also some excellent tools to aid the amp builder such as the turret lug tool and the bias checker. I got some of the potentiometers, the circuit board material, turret lug squashing tool and plenty of turret lugs, from here. Shipping speed and accuracy is always excellent.
  • Triode Electronics – From here I got the remainder of the pots, in/out jacks, pilot light assembly, tube sockets and the fuse holder. Shipping very fast as they’re only about 100 miles away.
  • Angela Instruments – With a windfall from my birthday (thanks mum!) I was able to buy the output and power transformers. Shipping has always been VERY fast with this company too.
  • Ace Hardware – I was somewhat confused as to why I needed a SPST for the standby switch, but a DPDT for the main power switch. SPST is easy…it is an ON-OFF switch for one circuit, hence single pole, single throw. It was soon revealed that the DPDT was going to switch both the live and the neutral wires coming in the power connector. This guarantees that there will not be any 120V AC in the circuit when that switch is off. Time will tell if these switch are as good as the Carling brand, which seems to be the defacto standard. Shipping very fast indeed as they are a two minute walk from my house 🙂
Transformers and an EL34

The transformers and an EL34

So I was lucky enough to have the shipping gods smile on me and I had everything ready to go. I was not however lucky enough to have drilled the holes the correct sizes last time. After 20 minutes or so of measuring and re-drilling, I was done. The last job was to use a jig-saw to cut the power connector square, which went well. I then trimmed up every hole possible with my Dremel. This helped get rid of any burring or uneven cuts.

Next I basically attached as many parts as I could to the chassis. I already had some #6 and #8 screws/nuts so I could use them to fasten the tube sockets. I’ll need some more for the transformers…oh and I’ll need 4 rubber grommets to protect the transformer wiring. If you are familiar with the AX84 P1eX design, you will notice that I have way more 9 pin sockets than required. I decided to do this to give me more options in the future. For instance I can switch to a noval output tube, such as the EL84. Or I could add more gain stages…or use more 12AX7s for reverb or tremelo. I am hoping this amp is going to let me experiment and therefore learn.

Whole chassis

The whole chassis looking more and more like an amp

If I had a time machine, I would’ve naturally drilled everything the right size first time. I have no excuse except for not having the parts when I drilled. Working from the chart seemed to confuse me, and I haven’t yet worked out why. I’m thinking that the size markers on the step-bit I used were literally out of line. This meant that I was always one step too small. The second time I drilled I measure the parts with my calipers and was able to choose the correct step imemdiately. Lesson learned 🙂

Next step, the circuit board and the actual electronic components!

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