Dig it! Saint's Epiphone Valve Jr Rebuild

[Modern Saint]

Just when you thought it was safe and over, the Saint decides to take another amp project. This time it will be a rebuild rather than a full build. The victim is an Epiphone Valve Jr head that was bought for $60 about a few months ago. What inspired this build was that I got to play one at the LA Amp show back in September 2010 through a Marshall 4x12 cab with a stock Fender Strat in the Mercury Magnetics room. The amp was very responsive and dynamic using the guitar’s volume control and the sound and tone was just incredible and sweet.

Anyway because of my positive experience with the Mercury trial, I chose to mod this unit with the Mercury Magnetics product. Now if you search the Internet for mods, you will find tons of information plus other vendors offering the OT and PT transformers such as Heyboer or Hammond. While they are good products, what I heard with the MM setup was magic and that is what I am after. One comment that was made on the net was: “Why does the mod need a choke?”; “Why spend the extra money?” Simply put, the better the DC voltage on the unit, the more efficient the amp will run. Mercury Magnetics is more expensive in general – read about them at their site and make your own judgement call.

The purpose of the mod is to improve the performance of the EVJ amp. Some of the problems with the stock unit is the Power Supply. There is a lot of inherent noise and the filament voltage is too high (about 7-8 volts DC, should be 6.3 VAC) which will shorten a tubes life. In the old days when tubes were in car radios, they did run off of DC Voltage. The Output transformer also needs to be beefed up if you are replacing a PT.

As for my application of the Epi Jr rebuild, it will be for recording with the amp full open through my isolation cab.

Here are the parts needed to start my build.

The Mercury Magnetics Kit (www.mercurymagnetics.com)

I ordered this yesterday and I got it this morning via UPS Ground only because MM is also in Southern California

Box Detail Top

Box Detail Front

Box Detail Right

Box Detail Left

Here is the excerpt from the "Read Me" doc on the disc for those who are interested in doing this in the future.

Thank you for purchasing Mercury's Upgrade Kit for your Epiphone Valve Jr.
As of this writing, there are at least 3 different PCB (printed circuit board) versions of the Valve Jr.

Please read the introduction material in the manual to determine if you have a Version 1, 2 or 3 PCB Valve Jr.

Version 1 PCBs are relatively rare and Epiphone made several major changes immediately after its release. The most common are Versions 2 and 3. They're all easy to identify from our instructions.

There are 2 different manuals on this disc, one for the Version 1 PCB and the other is for Version 2 and 3 PCBs.

Version 2 and 3 PCBs are virtually identical with only a couple of component values changed between them. However, you should verify all components on your amp's Main PCB to be sure. Epiphone occasionally makes unannounced alterations that could affect your upgrade.

From the reports we've been receiving, it's apparent that some Version 3 PCBs are experiencing component failures (from the stock components, not Mercury's Upgrade). We recommend that you test your amp BEFORE making the Mercury Upgrades just to be sure it's operational.

The kit includes all the components you'll need for all versions, including the "6V6 Mod" (however, you'll have to supply the 6V6 tube) and an "Anti-Squeal" option. The "6V6 Mod" gives you additional tonality and tube variations.

The "Anti-Squeal" option is only for SOME Version 3 PCBs — do not install it if it's not necessary. However, if you have one of the "squealers" the correction mod is there for you.

If you encounter any problems interpreting what needs to be done, please email me at the address below. I'll look into it for you and get you an answer (usually within a day). Mercury's Upgrade Kits are in an constant state of evolution — and we're releasing updated versions 2-3 times a year. Information we get from your feedback is utilized for updates and future kits. And is always welcome and appreciated!
We're also looking for sound samples, stories and photos of Mercury Upgraded Valve Juniors. All submissions are welcome.

The kit includes a bag of electronic components (resistors, caps, 8-pin socket, wire and hardware), an Axiom PT, an Axiom Mini-Choke, and an Axiom OT. For instructions the box has a CD-Rom that has the instruction/installation manual for the EVJ Version 1 and Version 2-3. Also included are extras: sound samples, a how to solder doc, Sergio’s amp clinic video and a read me doc.

The bubble wrap removed and here are the contents.

Watts Parts, Board and Layout – www.turretboards.com

 

[Mark Wein]

 

[12Pack]

Doooooooooooooiiiiiittttttttt

 

[BoomBoomBigelow]

Dude00

 

[BoomBoomBigelow]

Have you been overcome by solder fumes? Any progress?

 

[Modern Saint]

The is update to the update originally posted on Saturday which was lost.

The Watts board 85% completed. This was performed a few months.

On Saturday I spent time working on this rebuild as I am waiting for another tool for my refret jobs. What I did was strip the chassis clean of the old setup. I was originally going to rebuild the old setup, do some clips and then tear it down but I realized, aw just screw it because the end result is what I am after anyway.

The Front Face

Bottom View

Chassis Reveal

Test Fitting the Watts Board. This is a Version 2 Epi Jr.

Reverse View

Holey Moley - New holes were drilled for the new MM Tranny's and added 6V6 tube. This process was hell as my stepper bit worked great until the 1 inch diameter which is what I needed. Even lube cooling still made it difficult. I had to break out the dremel to finish.

New MM Tranny's are installed along with 6V6 socket

New Front View with Switchcraft Jack and Alpha Volume pot added. Also note open hole on the right for a Standby Switch to be added.

Rear Shot of the Epi Jr with the MM Tranny's

The rebuild will continue and I am also planning to recover this little beast. More to come as completed.

 

[Mark Wein]

Nice! I'd be curious to A/B it with mine since they are different mods.

 

[Chad]

I really wish I had the time, skills and money to do this kind of stuff. Looks awesome Saint.

 

[Modern Saint]

Nice! I'd be curious to A/B it with mine since they are different mods.

When I tried it out at the LA Amp show, I only played through it dimed. That is what sold me as I want to use it more for home recording through the Isocab. It will be cool to A/B them.

I really wish I had the time, skills and money to do this kind of stuff.

I had to save up for it bro. I was first introduced to the mod in Oct 2010. The hardest part was finding an Epi Jr cheap enough to scrap. It is sad that the only thing original will be a few wires, chassis and housing. I am going to sell the guts on ebay to recover some costs - won't get much.

 

[BoomBoomBigelow]

I had posted all kinds of pics, pertinent questions and comments which MS remembers (I hope), which were lost in the database backubortionthingy. Not to mention a possibly Grammy winning song forever lost, but any way, some day I hope to post clips of my mod, but looking forward to Saint's results.

 

[Modern Saint]

I had posted all kinds of pics, pertinent questions and comments which MS remembers (I hope), which were lost in the database backubortionthingy. Not to mention a possibly Grammy winning song forever lost, but any way, some day I hope to post clips of my mod, but looking forward to Saint's results.

I haven't forgotten triple B!

 

[ellengtrgrl]

I'd do it (it's easy enough to do), but I don't feel ike dinking around with making a master volume or power scaling circuit for a VJ. The VJ sounds best when cranked, and there is no way I could crank one without getting evicted. I'd need a maser volume or power scaling.

 

[Modern Saint]

I'd do it (it's easy enough to do), but I don't feel ike dinking around with making a master volume or power scaling circuit for a VJ. The VJ sounds best when cranked, and there is no way I could crank one without getting evicted. I'd need a maser volume or power scaling.

Boomboom's erased post showed his which had the master and preamp volume + tone control. Mine will be used with an isocab so the volume control will be dimed to utilize the amp fully.

 

[BoomBoomBigelow]

Here it is again:

Pentode/Triode: Changes the operation of the EL84 to triode mode which cuts the wattage and gives more headroom

Chill/Party: IIRC changes the bias of the 2nd stage of the preamp.

Plain/Frosted: Can't remember. something similar to the above, probably on the 1st stage.

Volume knob is volume knob. Between 1st & 2nd stage of preamp.

Gain Knob is pre volume knob and drains to ground some of the 1st stage gain.

Master vol is just pre power tube EL84 and has some cap balancing to compensate freq changes that follow adjustment.

Also on the back panel is a Negative Feedback loop in/out switch.


Mod St. posted some pics of his excellent turretboard work and I commented that it was a wise decision because modding PCB's is a PITA.


Should anyone be interested, The EV Jr. is highly recommended as an excellent entry point to amp moddin/building, because of the low cost & simplicity of circuit design. They can be had for $100 to $130 maybe??? And there are several Monster websites devoted to this amp's potentials. http://www.sewatt.com/ for one.

 

[Scott Harris]

I did the Watts Valve Jr replacement board and output transformer on my Valve Jr combo. Less complicated than the whole Mercury Magnetics upgrade but still a much cleaner sounding amp.

 

[Modern Saint]

I did the Watts Valve Jr replacement board and output transformer on my Valve Jr combo. Less complicated than the whole Mercury Magnetics upgrade but still a much cleaner sounding amp.

Agreed on that Scott. My reason to going with the MM upgrade was that I got to play through it at the LA AMP a few years ago. There upgraded model through a Marshall 4x12 was simply amazing and would be ossum to use in a small venue as well as through an isocab for recording. I have played through a couple of other Jrs with different mods and they are like day and night. In fact, one of my buddies sold me another one last year (modded) for a dirt cheap price. Eventually it will turn into something else as well.

As for my own unit, been so busy with other things in my life that I need to be done that this project was put on hold. My hangup when I stopped was reaming out the hole for the 6V6. I think I will bust this out and resume as I not far from finishing it. so I finish it and now feel motivated to complete it.

Thanks for post Scott because I forgot all about this project...too many dang projects - sheesh.