Epiphone Valve Jr. Minor Mods

Hey, I didn't follow up on the upgrade due to time and cost concerns. I tried to promote a deal with Mercury to give me the upgrade and for me to document the installation. The best deal I could come up with was Technical Support from East Coast Music Mall maybe a small discount with a mention of the blog in a Mercury ad.. So this project was placed on the back burner.



BE CAREFUL, amps and tube amps in particular have the ability to store electrical energy after being unplugged.

ALWAYS unplug what you are working on, allow time for capacitors to dissipate.


I'm commited to the Mercury Transformer Mods, but I realized that others may not want to invest in such a radical modification as that. So, I'll also provide mods that I found address various issues with the Valve Jr.

The web site below has mods that address hum or noise the amp makes at rest and that must be overcome when producing noise (music hopefully). The author writes that he switches to dc power and shows how this can be done. Epiphone has updated the Valve Jr to this type of power to address the hum issue.




The website http://www.valvejunior.com/ has the below circuit diagram and a list of low budget mods that the web site creator has tried. I found it helpfull it eliminated the need for me to purchase a replacement speaker. I was looking at a Jensen replacement which the author tried but found the original better. On another site the author tried Sovtek tubes but found them to "brittle" sounding. I still might try a couple of tubes from Groove Tubes.












Again the author of http://www.valvejunior.com/ wired in some extra valve caps to adjust the tone and even wired in a small light to act as voltage attenuater or power soak to create an over driven sound at lower volume.







The added valve caps.

This diagram shows the added valve caps, light bulb power attenuater and a couple of tone mods. I've read through the low budget mods, I think I'll invest in the Mecury Mod.

The Following are tweaks improving or correcting the Valve Jr. circuit design.

March 16, 2007

Erik Miller, Euthymia Electronicshttp://www.euthymia.org/

The Epiphone Valve Junior amplifier seems to have been made for modding. Inexpensive, mechanically rugged, plenty of empty space inside the chassis.

The stock speaker is a decent clone of the Weber Ceramic Signature 8.

This is a collection of relatively simple modifications to the electronic circuit. They can be performed by knowledgeable DIY'ers or professional amplifier technicians.

The first thing to do is swap the stock EL84 out for a JJ or your preference of EL84. The Sovteks that I've seen in these do not sound good, at least in this application. I like the JJ.

The most important one is the Input one; it eliminates a great deal of noise and adds sparkly goodness. If you are not familiar with the standard safety procedures for repairing tube amplifiers, refer this work to someone who is.

There is enough voltage in the Valve Junior circuit to injure and even kill.

The component reference designators I use are visible on the PCB's top silkscreen.

Stock Valve Junior Schematic

Input mod

1. Remove R2 (68K), replace with 22K.

2. Remove R1 (68K).

3. Add jumper from input jack PCB header Ground pin to Ground side of R8.

4. Remove input jack, replace with one with nylon shell (Switchcraft N112A or equivalent).

5. Add 1M (or 2M2) across tip and sleeve of input jack.

What this does As designed, the single input of the Valve Junior is a copy of the #2 or Low jack on a typical Fender-type circuit. There is 68K in series with the signal, with 68K to ground to attenuate the signal and provide a path to ground for V1a's grid.

We are reconfiguring the Junior's input to resemble the #1 or High jack on a Fender.What we have done in step 1 is increase the signal going to V1a grid by lowering the value of R2 (the Fender's series input resistance is effectively 34K; we're dropping it another notch).

In steps 2 and 5, we've also increased the value of the resistor to ground, and moved it to the other side of R2. This has the effect of bleeding less signal to ground and increasing the effective input impedance of the amp.With more signal feeding the V1a stage, it contributes less noise, and just plain sounds better. This stage even after this mod has plenty of headroom. Passive guitar pickups will sound sparklier and more alive with the higher impedance.

In steps 3 and 4, we correct a grounding mistake. As designed, the ground path for the input jack is the chassis. The rest of the circuit on the PCB connects to the chassis near the opposite corner. This difference results in lots of hum coming from the input circuit. We isolate the input jack from the chassis and obtain a ground connection near R8.Interstage gain modInstall a jumper across R6 (1M).

There is an extra set of holes marked for a capacitor that may come in handy for jumpering across R6. If you want to be adventurous, you can even install a single pole switch here to allow you to switch to higher or lower gain. I suggest you just go with the jumper.What this doesAs designed, the amp throws away a lot of signal in the form of an extra voltage divider right before the volume control. This has the same effect as a 1M volume control set at midpoint. One volume control is plenty, and still works great. This mod allows more signal to get to V1b, also allowing it to operate more efficiently.

If you want an even earlier crunch, you may remove R7 as well.Power supply filter mod(be sure to discharge the power supply electrolytics before installing this mod!)Solder a 47uF/450V capacitor in parallel with C6.What this does Even after doing the above input jack mods, the amp has a noticeable 120Hz hum. I traced it to excessive ripple in the first DC power supply node.

This mod increases power supply filtering, resulting in a reduction in the 120Hz buzz.

Output impedance switch

The unused red wire coming from the output transformer in the Valve Junior is actually for 8 ohm output. Drill a hole to the right of the speaker jack, install a SPDT toggle, connect the tip of the output jack to the switch wiper, and the red and brown wires to the two other lugs on the switch. This allows you to match the output impedance of your amplifier with that of an 8 or 4 ohm speaker cabinet by flipping the switch.

Epiphone Valve Jr.

OK, Most of the following is from the Ebay ad. for essentially a cabinet, amp and speaker. The ad following the description for the amp is the modifications to be performed using the Mercury Magnetics kit. This is an experiment, I wanted to build an amp for a while and this opportunity availed itself. In the end I hope to have a boutique quality recording amp for under a grand.

"Custom made in Nashville TN! The Billy "G" custom made Western Style amplifiers! Features Pine and hardwood cabinet construction. Hand tooled leather leather handle. The actual amplifier installed in the custom cabinet is an Epiphone Valve Jr. Seeing is believing! I was very impressed when builder Graham Nichols brought this amp into the shop! Custom orders are welcome!Please add $40.00 for S&H. Thanks for looking! Franklin Guitar & Repair1912-B columbia PikeFranklin, TN 37064615-595-2268"

PAGE 1 PAGE 2Mercury MagneticsTransformer Demonstration Project

"The Valve Junior FEATURING the Mercury Mod

The Mercury Mod kit for upgrading your Epiphone Valve Jr. (combo or head)
Can you really get RECORDING QUALITY tone for less than $400?
YES you can! And change forever what you thought you knew about guitar tone.
Background: Inside of all the greatest-sounding amps ever built lies buried treasure. The source of this profound and amazing amp tone is the transformers. Pro-quality transformers are not easy to make and they are also expensive. When an amp builder is unaware of, or chooses to ignore this fact by installing cheapo transformers, the tone of the amp tells the tale.
If you find playing your guitar fatiguing or just plain boring, if your childhood memories of Uncle Bob's "armpit far concerts" sound better than the amp you're stuck with, then you are probably an unwitting victim of tonally anemic, low-budget transformers.

"If my place caught fire, my Mercury Modded Valve Jr. would be one of the first things I'd drag out to the sidewalk... despite the low cost."
-- Bob DragichVintage Guitar MagazineCLICK HERE TO READ FULL ARTICLE
To prove the point, Mercury has designed a Mercury Mod for the remarkably inexpensive Valve Jr. amp (combo or head). This demonstration upgrade kit features high-end pro-quality performance transformers like those in great-sounding amps costing anywhere from hundreds to thousands more. Our upgrade is the lowest-cost introduction ever to the wonderful world of boutique amplifiers.
This means you can experience pro-grade tone with all of the feel and expanded range-of-control the pros enjoy -- without draining your wallet!
Give Paul Patronete or Patrick Selfridge a call at (818) 998-7791 and get started on the right path to pro-quality tone today!
"I finished the Valve Jr. mods over the weekend. AMAZING!!!!!!!!!! I have been playing guitar for 21 years and this is, without a doubt, one of the best amps I have ever played -- and it only cost me $400 total!!!!! Unbelievable!
I had a longtime guitar-playing friend over on New Year's eve and we recorded all night long with the Mercury Mod Valve Jr. Needless to say, he wants one and will be ordering the amp and kit VERY SOON!!! I am eventually going to order a second kit so that I can run them in stereo. Can’t wait to hear what this thing sounds like with upgraded tubes.
I have a new found respect for the iron that is used in all my amps... and more specifically for the fine people/engineers at Mercury Magnetics. As a budding DIY amp builder, all my new builds will be using Mercury Magnetics trannies. Way to go!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
-- Jonathon Short
About Mercury's EVJ project: Ever wonder how much better YOUR amp could sound just by upgrading its magnetics? Here's your chance to discover the night and day difference. On occasion we'll get a couple of identical amps sent to us for A-B testing purposes. Typically one of the amps is kept bone stock while the other gets the Mercury transformer upgrade treatment. The results are always dramatic -- with rich, lush improvements in tone and harmonics, and the distinct absence of ear-fatigue that only enhanced magnetics can reveal.
In-house, we call the "B" in these tests the "Mercury Mod" version. These A-B tests have always been popular around here and are responsible for thousands of converts to our cause.
"Update on my Valve Jr. upgrade! Wow, nothing but kick ass, balls-to-the-wall tone!"
-- Gilbert Cruz
That set us to thinking about conducting an A-B test on a fundamental guitar amp. One with only the minimum components to do the job. Hummm....
After a little digging around we found our guinea pig -- the Epiphone Valve Junior Combo (thank you Bob Dragich). Talk about your fundamental (and remarkably inexpensive!) tube amp. Check this out:
5 watts
Single-ended, Class A
One generic 12AX7 preamp tube
One generic EL84 power tube
Generic power & output transformers
Generic 8" speaker
Epiphone's Valve Junior combo proved to be an almost ideal demonstration platform because it is such a basic, stripped-down tube amp. Just 2 tubes, 2 transformers, 1 speaker, a simple circuit board and just a handful of other parts -- along with 1 input jack, 1 volume knob and an on/off switch. That's it, no computerized components, no tone knobs, no added f/x circuits, nothin'... you just can't get any more elementary and still have a playable tube amp!
"The amp tech was floored. He couldn't believe the tone. I highly recommend this insanity!"
-- Craig Lunsford
All this for about $139.00 for about? Yes, but as you might expect, the stock amp is anemic and thin sounding -- not exactly an inspirational amp. Let's see, what can we do about that....
Side note: It should be mentioned that our goal wasn't to build the perfect amp, only to demonstrate the effect of quality magnetics. But it quickly became apparent that we'd transformed the little Valve Jr. amp into an extraordinary "I've gotta record with this!" keeper. As the demands poured in we decided to develop the Mercury Mod into a kit and make it available to the general public.
"Holy smoke, I thought the amp was going to get up and walk around!! Are you doing mods like this to other amplifiers? Very, very impressive complete tonal spectrum sound! Nice job."
-- Marcus Earling
The Mercury Mods....
The project was headed by Mercury's Sergio Hamernik, and Los Angeles-based amp tech wizard, Alan Cyr (http://www.amp-exchange.com/). After examining the original circuitry several custom Axiom®-series transformers and Mini-Choke™ sets were designed and tested, as well as several circuitry mods to correct flaws in the original design.
Alan and the Mercury team spent several weeks working on the little amp before deciding upon the best-sounding combination of mods and adaptations. A bonus was Alan's ingenious, yet deceptively simple circuit corrections.
Along with a custom-designed set of transformers, and much needed clean-up of the circuitry, the amp remains stock. If you are an experimenter you may want to try different speaker and/or tube configurations, but oddly enough, those components deliver relatively minor tonal changes compared to the absolutely H-U-G-E improvement of the Mercury trannys. The result is a remarkably harmonically responsive & toneful little amp that runs quiet and sounds B-I-G. No wonder so many LA session players are grabbing them up and heading to the studio!
We've definitely transformed the bland little Valve Jr. Combo into a keeper. Here in Los Angeles, the Mercury Mod Valve Jr. is one of the hottest, most in-demand insider amps around. Those who've heard it immediately want one -- and at such a low cost to make the mods, who can afford NOT to!"

The Phoenominal Les Paul

A 1957 Gold Top selling for $80,000.

A 1953 Gold Top selling for $50,000. I prefer the single coil P-90 and the single tail piece. The intonation may not be spot on but the tone makes up for it.

'58 Les Paul Custom 3 Pick Up @ Gruhn Guitars $40,000

'57 Gold Top Les Paul Std. @ Gruhn Guitars $110,000

Duane Allman's '57 Les Paul Std. Tobacco Sunburst Price ?

My '87 Les Paul Custom maybe $2000

Reissues from $4,000 to $20,000 depending on exclusivity

Dickie Betts' Lp reissue $5000 to $10000

Again unknown, Guess - $10,000

My mid 70s Gold Top $1500 or so. Maybe more.

Bob Welch's LP ex-Fleetwood Mac Guitarist ("Sentimental Lady") $8000


I have to address the recent explosion of '50s Les Pauls. Sunbursts have always lead the market, now regularly over $100,000 they even dragged Gold Tops up too. Not bad for a guitar that sold for $267.00 in '55. The rise in price has dragged up all Les Pauls even new ones are going for crazy prices and I don't think they play or sound that great.