Final pictures of amp

I added labels using a paint pen to the front of the amp, so others can know what each switch or knob does. It felt so good to finally put screws into the amp, and seal it up for the last time.

Footswitch Install

I drilled a hole for a 1/4" mono input jack, which has two terminals. After many attempts testing the input, I discovered which terminals should go where. One terminal is wired to the ground of the volume pot, and the other is soldered to the JP1 jumper switch. I tried multiple locations of where the second solder should be, included on both sides of R6 and R8. Across R6, it eliminated the push-pull option for the tone pot. Across one terminal of R8 created a mute button, which just silenced the sound output when pressing the foot switch. On the other side, the button created a metronome style click, which is useless.

The foot switch is a single button, SPST Johnson foot switch. The cheapest one on Amazon. I like the way the switch is wired up now. When the JP1 switch is off, the foot switch barely notches up the volume. If JP1 is up, then the foot switch toggles a louder, cleaner volume output. This easy volume boost is useful for playing solos live.

Paint it Black

I painted the front of the amp chassis black. The black is a special black, GM black. That means it is the same exact black as my Cadillac. People write songs about black Cadillacs, and now I have an amp that is as black as a Cadillac. I will use this amp to write songs about how black this amp is.

Anyways, since this is car touch up paint, the painting took forever and is very uneven. This gives it a unique textured look.

BitMo Push-Pull Tone Installed

Today, I installed the Push-Pull Tone control to the Valve Jr. This mod, which I bought from BitMo, uses a DPDT attached to a potentiometer, a resistor and a few capacitors. The potentiometer is wired up similar to the volume knob potentiometer, with the left-most terminal being power, middle being the wiper (variable), and the right being ground. The tone of the amp is affected by the bottom two terminals of the DPDT when the pot is in the "down" position. This is just one small capacitor (once again, I'm not supposed to disclose values. I think). When the pot is in the "up" position, the upper terminals of the DPDT is used, which is using three capacitors and a resistor. The external wires for the pot were soldered to two resistors already on the Valve Jr board, R6 and R8. Capacitor C4 was cut off of the board, to be overridden by the new pot components.

The result: This tone knob adds a great more tone options (of course) to the amp. When turned all the way left, or counter clockwise, the bass is super high. The resulting sound is mellow and jazzy. Towards the right, the treble is picked up, and it sounds incredible paired with a distortion pedal. Using the push-pull option gives you even more diversity with the tonal range. There are so many different styles of sounds I can get from the amp now, especially paired with my pedal board. I don't know what else I can want from an amp. Pictures below!

Starting soldering caps to the DPDT.

Soldering pot across two resistors on top of the board.

Current inside of amp. 

All mods visible.

Rear of recent mods.

Trio mod (far left), volume pot (left), tone pot (right), and bright switch (below, with green wires).

Amp Tested with Pedalboard

I tested the amp tonight with my pedal board, so I got to run distortion through the amp for the first time. It sounds great, and surprisingly has no hum anymore. Either the pedals eliminated the feedback, or it just went away during the hours I wasn't in lab. This might have been because of interference from things that were on in Broun Hall.

BitMo Trio Mod Install

I got the BitMo Trio Mod in today, and I started working on installing it. It has a a scary copyright notice on the front saying I can't say what it does, blah blah blah, so I will only describe what it does and how, rather than describe the components it comes with and the direct connections.

This mod consists of two parts: a DPDT switch and a push/pull potentiometer with a DPDT switch attached to the back. If the pot is in the down position, it uses one set of the DPDT's poles, and if the pot is in the up position, the other set of the DPDT's poles are active.

The first mod only uses the DPDT switch, and works as follows.

First of all, DO NOT BREAK THE DPDT SWITCH. I have done this twice already. Make sure not to overheat the switch, and only solder it when in the "Off", or middle position. There is an option for both a Version 2 and Version 3 Valve Jr. Mine is the Model 2, but I have changed R1 to 1 Mega ohm, so it has the same affected component as the Model 3 amp. However, I chose to use the Model 2 schematic. To do this, cut R1 off from the main board and make two connections on to the end of R1, and to the place on the board where R1 previously was. If you did the Model 3 mod, you would keep R1 soldered in and solder these connections in parallel.

• Option 1: "Bright." Straps a small "bright" capacitor in parallel with the volume pot output. Fender imitation sound. This setting has great gain. When you hit the strings hard enough, you've got a good classic rock tone already. 
• Option 2: "Brit." British style sound, increases impedance for great mids. My favorite setting as of now, super clean and mellow, no matter how hard you pluck. 
• Option 3: "Brat." Straps an extremely small capacitor with the volume pot output. Cuts the lows. So much treble. 

At first, I couldn't notice any difference, and just more hum. After playing a few chords on each setting, I noticed a major difference in each channel. I think the hum could be cut by using some insulation for the two long wires I used, shown below.

I covered the two long thin, orange wires with yellow electrical tape, and pulled two wires from the insulated wire that came with the kit that I did not use. So now, all wires should be insulated, and there are no unused wires floating around. Result? No less hum. It might be interference, since the DPDT switch is right next to the volume pot. That was advised against. I might build some sort of smallmouth Faraday cage to isolate the issue.

Notice the long orange wire to R1 from the DPDT.

Current front of the amp. New DPDT switch is far right, and new push-pull pot will be above the input (hole already drilled).

Updated Components Continued

The amp was way too quiet for my tastes, so I made two more changes. First, I took out R7. This value was originally 1 Mega ohm, but I changed it to 100 kilo ohm. Now it is nonexistent.

Originally, R2 was 68 kilo ohm, but I lowered it to 47 kilo ohm originally. Next, I lowered the value of R2 down to 10 kilo ohm.

Below is a schematic of the Valve Jr, Version 2. Ignore those arrows, that isn't my work. As you can see R7 was used to bring the signal down, as it goes straight to ground. This is useless for what I want, so it is gone.

R1 and R2 are in parallel on the guitar input jack. Since I changed R1 from 68 kilo ohm up to 1 Mega ohm yesterday (HUGE INCREASE), I decreased R2 much more. Since R2 is actually before R1 in the circuit, it creates a voltage divider which decreases the signal right when you plug in your guitar. Making R2 smaller will give less signal loss. One modification option I have in the future is to move R1 in front of R2 in the circuit, which would decrease the voltage divider even more. 

Un-modded Valve Jr Version 2.

The results? Sounds incredible. The amp can get loud again, which is what I wanted, and the mellow sounds when you turn the tone pot down on the guitar and use a neck pickup is incredible. I love this amp and the way it sounds so far. I have been working on my pedal board at home, and I'll bring that in next week to play some pedal through the amp. I haven't played anything but clean on it so far.

Changed Components Successfully

This morning I changed the following components:

• R1 to 1 Mega ohm. Was originally 68 kilo ohm.
• R2 to 47 kilo ohm. Was originally 68 kilo ohm.
• R6 to 100 kilo ohm. Was originally 1 Mega ohm.
• R7 to 100 kilo ohm. Was originally 1 Mega ohm.

To get to the bottom of the board, I temporarily removed the tubes to have more access. I also removed all the cables to the Transformers, as those limited the mobility of the main board. This was my first time using de-soldering braid, and it is probably the greatest invention ever. I don't know how I lived before knowing about it. When I was done, I made sure to put the tubes in, and then connect all of the Transformer wires to their proper pin. The connector for the T3 broke off while I was pulling it from the board, so I stripped the end of the wire and re-soldered the tip to the connector. Now it's better than new.

Anyways, these modifications are intended to make the potentiometer change, or volume change, more linear. Before the change, it would be really quiet, and then really loud, with not much in between. Now, the change is noticeably more linear, with the volume ranging evenly from quiet to loud. This does have some trade-offs though. The amp is almost silent until about 10 o'clock on the dial. Maybe it's because I'm almost deaf because of all those years of rock n' roll.

Also, those DPDT from Hong Kong never came in, so they're sending me two more. Maybe those will actually arrive.

Here's some pictures:

With all components changed.

R1 and R2 successfully soldered in.

The back of R6, before clipping the excess resistor wire.

Change Components Plan

After figuring out I can't solder on miniature switches today, I've decided to go a new route and change some components on the main board. I will change R6 and R7 to 100 kilo ohm resistors. This will bring R6 up and R7 down. I will use the 1 Mega ohm resistor from R7 and put that in R1, and change R2 to 47 kilo ohm. R1 and R2 directly affect how much the volume knob changes the output volume. I discovered today that any resistor connected to ground will change the gain, and a capacitor connected to ground will affect the tone. I also discovered de-soldering braid, and how to use it, so these components will be changed in a flash.

Tonight, I ordered the Bitmo Trio mod, which contains a secret list of parts (I could not find a part list anywhere). Anyways, it will add a Push/Pull Tone knob (potentiometer) and some sort of 3-way switch. I'll find out soon enough. I also plan to inverse the orientation of my amp (turn it upside down, permanently). The heat dissipates better this way, and I also want to change the look of the head.

Installing Bright Switch

I'm at the lab currently, trying to install a "Bright" tone modification switch, using a DPDT switch. This should put a capacitor in parallel with the potentiometer, but it is just making my amp really noisy so far. I double-checked my wiring, and I think I have 1a bad design.

I checked to see if the DPDT switch was causing all the noise by taking the wiring out of the pot, and the switch circuit was causing all of the noise. Now to debug.

I think a root cause could be the type of capacitor I am using could be wrong. The modification called for a 120pF silver mica capacitor, which I used earlier to replace a broken cap. I am currently using a 100pF ceramic disk cap, which seems to handle higher voltages worse. Amps seem to use these silver mica capacitors exclusively because of their reliability and ability to handle high voltages.

I tried changing the capacitor to an electrolytic capacitor, with the same negative results as before.
I tried using the SPST for a few things. I strapped a 1Megaohm capacitor across the terminals, and then hooked that up to the input and ground of the cap. More buzz.

In other words, today, I tried a bunch of things, and they all just created a bad hum for the output. I have reverted it all back to the way it was at the beginning of the day, and I'll start again tomorrow.

Tube Updates

Right before I left for break, I had installed the new JJ Tubes. Well, after a day, they did not work anymore. There was no sound output from the amp, and the tubes were not lighting up. So I pulled the tubes and put back in the stock tubes, which I knew were good. Still no lights from the tubes, and no sound output. I pulled all three fuses for the tubes and replaced them. Then I got lights in the tube filaments and sound output from the speaker. Success.

So then, I changed the tubes back to the new JJ Tubes. Well, I thought I did. You have to unscrew 9 screws to get to the tubes, then re-screw them all in to make sure the main board is stable. I did that, then realized that I had only changed the power tube to JJ, and taken the pre-amp old tube out, and put the old pre-amp tube back in. So I unscrewed everything and replaced the pre-amp tube with the new tube. Phew. Success.

I was tired of waiting on this Hong Kong seller to send me my DPDT switches for the "Fat" and "Bright" switch, so I drove to Radio Shack and bought some. They're small, so I need to drill new holes for them. I should have the new tone modifications in by the end of the weekend.

Also, I got the washer and bolt in for my potentiometer this week, so now the pot doesn't move around inside the chassis. I'll order some cool looking cover for it soon, or maybe 3D print one in the SPaRC lab.

I also drilled holes for and temporarily mounted my new DPDT switches. Looks fancy. 

New Tubes Installed

I was doing research on how to bias tube amps, and then I discovered that my Epiphone Valve Jr is self biasing. So just put the new tubes in and play. I replaced the Russian Sovtek tubes with some new JJ Tubes. I bought the JJ Tubes set from Amazon as a matched set for my amp. The new tubes are the same types of vacuum tubes as stock: an EL84 as the power tube and a 12AX7 as the pre-amp tube. With the JP1 bypass, the amp makes a substantial amount of hum. I think this is due to the tubes not being warmed up. I tested the amp immediately after turning on, and tubes need a few minutes to warm up before they sound good.

Tubes taken out.

Old Sovtek tubes.

New tubes (left) and old tubes (right).

Pictures of Updates

Tonight was exciting because I got to verify the potentiometer and play through the two new modes of my amp: Using the JP1 circuit (off) and cutting the JP1 circuit out (on). I noticed that the sound was noticeably louder, but also sounder cleaner when the switch was on. I also got to verify that my component swap went successfully. I accidentally knocked the C1 capacitor off with the drill, woops, and so I replaced it with the only Silver mica capacitor I could find. The stock C1 was .022uF (22,000 pF), and I replaced it with a 120 pF capacitor, which is much smaller. The amp sounds nice now, and I plan to get the tone modifying components in it soon.

New potentiometer. 

I had to unscrew the main board from the chassis...

To solder in the switch to cut out the JP1 circuit. 

Got the 2-way switch soldered in.

This was a tough solder job, as one solder spot was right next to that white connector. 

I drilled holes for all three switches, since I already had the drill out. 

Far right switch hooked up, other two are blank for now.

Attached the main board back to the chassis. 

Front of the amp currently. I'll probably remove the On/Off logos. 

Setup for E-Day in the SPaRC Lab!

Added On/Off Switch for the JP1 Jumper

So I ordered more on/off switches, since the ones I ordered from Hong Kong will arrive sometime in 2014... these new ones I ordered from America. The JP1 jumper on the Valve Jr. is pretty much a wire that brings the output circuit into contact with a capacitor, which decreases the quality of the output signal. I wanted to wire this out of the circuit, but still have an option to switch back to the JP1 circuit if need be. I wired the input and output of the on/off switch into the two JP1 holes after I removed the physical wire that was present before.

There was, however, one casualty. While drilling a hole for the one/off switch, I knocked the C1 capacitor off of the board. Like completely off, ruined capacitor. I haven't tested the circuit yet, but I assume this isn't good... I'll be looking up the value of C1 and searching for a high quality replacement soon. Anyways, using the drill was awesome. I used the largest bit available in the lab, which is 1/2". I originally had it drilling clockwise, and it wasn't getting through very well. I eventually tried reversing the direction of the drill, and then it went through the chassis with ease.

E-Day is tomorrow, so I will be displaying the amp and the current mods in the SPaRC lab.

Verified New Potentiometer

I did what everyone in electronics is warned against, and testing my guitar amp with exposed components. I lived, so it's all good. I verified that the new potentiometer, which is a variable resistor, works. Not well. As I said last week, my soldering iron sucks, so I have to take this back to the lab. I was going to wait until I got my 2 way switches in, but I just noticed I ordered them from Honk Kong. Which means 6-8 week shipping.

Anyways, I tested the new pot hanging outside of the chassis. It is scratchy, which means I have a bad connection. So I'll re-solder that soon, as well as drill a hole for it to fit inside the amp.

Pot Change on the Volume Control

I got a few parts in this week, including the matched set of JJ Tubes (EL84 and 12-AX7), the new potentiometer (for the volume control) and a 120pF Silver Mica Capacitor. I'm still waiting on a few switches to modify the JP1 capacitor out of the output circuit, and to add a "Bright" and a "Fat" sound modification.

Matched set of JJ Vacuum Tubes

Old pot.

Nice shiny new pot. 

Unhook this cable first.

Old pot on board on the left.

Both are 1Mohm potentiometers.

With the new OT, amp can sit upside down nicely. 

Had to add wires for the new pot. 

I installed the new potentiometer, but it was a huge hassle. The new pot's pins didn't fit inside the pot board, so I used some short wires to hook them together. I set up a lab at my house to work on this project, and just found out my soldering iron doesn't get hot enough to melt the solder on these components. I ended up borrowing my neighbor's gun for the time being, but I'll have to move back to the lab. The new pot is too thick to fit through the previous hole in the metal chassis, so I have to drill a larger one. I'll save this until I get the switches in, because I'll have to drill three holes for them anyways. 

The installation of the tubes I will save for later, so that I don't cause unneeded strain on the new tubes while I'm testing.