The Valve Jr transformation is complete....

[duhvoodooman***]

With the help of a couple of excellent online resources--including one familiar to us regulars here at TheFret--I finished my final (Really! I mean it!) round of mods on my VJr combo over the weekend. In addition to the previous changes I've made (chronicled HERE), I did a number of tone and feature enhancements that really put the exclamation point on this little tone monster's capabilities!

These additional mods I did are described in one or more of the following three sources:

Layboomo's Valve Jr Gold/Silver Mods thread @ the Epiphone User Forums

S2 Valve Junior Upgrade Kit Installation Instructions (The kit is no longer available, but the instructions are GREAT!)

Our own Tunghaichuan's Valve Jr. Web Page

On Tung's page, pay special attention to his new "Valve Junior Modifications eBook". I was privileged to be able to preview this impressive resource, and I can tell you that he did a comprehensive and thoroughly professional job on it! It's packed with detailed instructions, excellent supporting photos and diagrams, and a lot of useful ancillary information. If you want to undertake modding your Valve Jr and don't have a lot of experience with such things, this is a $20 investment that I'd highly recommend making!

Just one note of clarification here regarding different versions of the Valve Junior: Mine is the original version (i.e. "v.1") of the amp, and the circuitry is somewhat different than the 2nd and 3rd versions, which incorporate significant improvements. If you have the head rather than the combo, by definition you have v.2 or greater. The S2 instructions apply to v.1, though 90% of it is accurate for the later versions, as well. Both Tung's information and the Layboomo Gold/Silver mods apply to v.2 and up. The newest version is v.3, and differs from v.2 only in the fact that it has a better output transformer (OT) and somewhat upgraded tubes. Same circuitry, as I understand.

Anyway, after accounting for the mods I'd already done on the amp, here's a list of the additional things I changed or added:

Reliability & Safety Mods:

• Added a 20ohm 25W power resistor on the incoming AC to drop the EL84 plate voltage a bit (stock = ~340V, too high).
• Increased the power tube cathode resistor from 220 to 240ohm to cool the bias and reduce plate dissipation to under 12W (EL84 recommended max.).
• Replaced the dinky little 16mm stock volume pot with a beefier 24mm pot.
• Added a 220K "bleeder" resistor between the B+ rail and ground to drain the filter caps after power-down.

Tone Improvement Mods:

• Upgraded the cheap stock tone caps with 0.022uf Mallory 150's.
• Replaced stock rectifier diodes with ultra-fast UF4007's to reduce switching noise.
• Replaced the R6/R7 1M voltage divider resistors with lower ratings to "open up" the tone (used 330K/220K)
• Replaced 2.2K stock preamp cathode resistors (R8 & R9) with 820 and 680ohm, respectively. This warms the bias of the two 12AX7 triode preamp stages and gives smoother overdriven tone.
• Also replaced the stock 22uf preamp cathode resistor bypass caps (C3 & C4) with 3.3uf caps. This raises the bass roll-off frequency and gets rid of low-end muddiness in the bass.
• Stiffened the bias on the EL84 power tube by increasing the cathode bypass cap (C5) from 22uf to 1000uf. This gives the VJr a noticeably punchier sound, more like a fixed bias amp.
• Replaced the 100pf switchable ceramic "brightness" cap (optional open cap spot on the v.1 combo PCB) that I had previously installed with a larger 220pf silver-mica cap. This gives a stronger emphasis to the trebles and higher-end mids when the cap is engaged.

Added Feature Mods:

• Installed a standby switch (ridiculously easy mod).
• Soldered in a switchable 68K resistor in parallel with R6. When engaged, this drops the effective R6 resistance from 330K (per the 3rd tone improvement mod above)to ~56K, and doubles the gain voltage passed on from the first preamp stage to the second. In other words, it's a "gain boost" switch.
• Added the Tweed tone control shown on Tung's VJr web page.

Some of these mods are very subtle in nature and may not even be noticeable in their impact, while others have a very marked effect. But even the subtle ones are all moves in the right direction and are very inexpensive, so why not do them as long as you're "under the hood" anyway? The cost for all the parts for the 14 mods listed above came to under $16! The main thing these mods take is time and care in doing them. Especially when desoldering the old stock components from the PCB, care must be taken not to apply too much heat, or it's possible to lift the solder pads from the PCB surface. That generally can be repaired if it happens, but it's an added hassle.

The impact of all this work? Well, I really need to get a clip or two recorded & posted here, but together with my previous modifications, this little amp sounds just amazing now. The clarity and punch is light years beyond the stock version, and the gain increase is just scary! I can't even turn the volume knob past 9 o'clock in the small room where I play without deafening myself. Plugged into my 2x12 cab, I'm sure this puppy could be used to gig in a modestly-sized venue. And I really like the new features I've added. I'll post a pic or two of the front panel soon, showing the new switches and tone knob. I know some folks like the simplicity of the Valve Jr and it's single volume control, but I prefer having more tonal control than that. So now I have volume & tone knobs and toggle switches for standby, gain boost and brightness. I can hardly wait to get it into a bigger room and open up the volume so I can get that power tube into saturation! VROOOOOOM!!! :

[tunghaichuan***]

Duhvoodooman,

Thanks for the kind words. It took me about a year to write that book and I sweated a lot of small details.

Just one note of clarification here regarding different versions of the Valve Junior: Mine is the original version (i.e. "v.1") of the amp, and the circuitry is somewhat different than the 2nd and 3rd versions, which incorporate significant improvements. If you have the head rather than the combo, by definition you have v.2 or greater. The S2 instructions apply to v.1, though 90% of it is accurate for the later versions, as well. Both Tung's information and the Layboomo Gold/Silver mods apply to v.2 and up. The newest version is v.3, and differs from v.2 only in the fact that it has a better output transformer (OT) and somewhat upgraded tubes. Same circuitry, as I understand.

To be fair, Epi did change some of the circuitry from V2 to V3: they lowered the cathode bias resistors on the 12AX7 from 2.2k down to 1.5k, which is stock Fender value. These resistors bias the 12AX7 warmer and make the amp sound crunchier when driven hard. Unfortunately, they left the 22uF bypass caps on the 12AX7. These make the amp sound blatty when the amp is driven hard.

Anyway, after accounting for the mods I'd already done on the amp, here's a list of the additional things I changed or added:
[*]Stiffened the bias on the EL84 power tube by increasing the cathode bypass cap (C5) from 22uf to 1000uf. This gives the VJr a noticeably punchier sound, more like a fixed bias amp.

As an experiment, I converted my V2 VJ to fixed bias. I made a little negative bias supply board and ran it off of the 12-0-12v winding. (Version 3 does not have this winding, it is for powering the opamps on another amp the VJ's power transformer is used in.) It was hard to tell the difference between the VJ using the 1000uf cathode bias cap and the fixed bias VJ. Replacing the stock cap with a 1000uF cap is much simpler, and you don't have to install a board.

[LIST]
Some of these mods are very subtle in nature and may not even be noticeable in their impact, while others have a very marked effect. But even the subtle ones are all moves in the right direction and are very inexpensive, so why not do them as long as you're "under the hood" anyway? The cost for all the parts for the 14 mods listed above came to under $16! The main thing these mods take is time and care in doing them. Especially when desoldering the old stock components from the PCB, care must be taken not to apply too much heat, or it's possible to lift the solder pads from the PCB surface. That generally can be repaired if it happens, but it's an added hassle.

Have you considered replacing the PCB with a board from turretboards.com? I believe they make a replacement board for V1 amps. Those stock green PCBs *really* suck.

The impact of all this work? Well, I really need to get a clip or two recorded & posted here, but together with my previous modifications, this little amp sounds just amazing now. The clarity and punch is light years beyond the stock version, and the gain increase is just scary! I can't even turn the volume knob past 9 o'clock in the small room where I play without deafening myself. Plugged into my 2x12 cab, I'm sure this puppy could be used to gig in a modestly-sized venue. And I really like the new features I've added. I'll post a pic or two of the front panel soon, showing the new switches and tone knob. I know some folks like the simplicity of the Valve Jr and it's single volume control, but I prefer having more tonal control than that. So now I have volume & tone knobs and toggle switches for standby, gain boost and brightness. I can hardly wait to get it into a bigger room and open up the volume so I can get that power tube into saturation! VROOOOOOM!!! :

It really is amazing, isn't it? Take an amp that sounds pretty crappy stock, make a few changes and it turns into a real fire breather. Version 2 was an improvement over version 1, and version 3 takes very little modding to sound excellent. Some have even suggested that the stock version 3 output tranformer sounds almost as good as the Hammond 125ESE. For a Marshally sound, the V3 stock OT may even be better sounding as you get a little core saturation. The 125ESE will not saturate in a VJ circuit at all.

tung

[marnold***]

Version 2 was an improvement over version 1, and version 3 takes very little modding to sound excellent. Some have even suggested that the stock version 3 output tranformer sounds almost as good as the Hammond 125ESE. For a Marshally sound, the V3 stock OT may even be better sounding as you get a little core saturation. The 125ESE will not saturate in a VJ circuit at all.

So would you be happy using a VJ v3 out of the box or would there be a tweak or two that you must needs make?

[tunghaichuan***]

So would you be happy using a VJ v3 out of the box or would there be a tweak or two that you must needs make?

I just pulled the chassis on a V3 head I got a GC a while back. I'd probably do a couple of tweaks:

Replace one of the power supply resistors with a higher value to cut down on the B+ voltage.

Rebias the EL84 with a 270 ohm resistor.

Replace the cathode bypass cap on the EL84 with a 1,000uF cap.

Replace three key resistors with 1W metal film types; the 1meg grid load on the first 12AX7 triode and the two 100k plate load resistors on the 12AX7.

Depending on whether or not I would be cranking it up all the way or not, I'd change the cathode bias resistors on the 12AX7 to 680-820 ohms. I'd also swap out the bypass caps for 2.2uF to 4.7uF caps.

I'm still debating on swapping out the stock V3 OT for this Edcor OT. The one I have is actually the multiple secondary version for use with 4, 8, and 16 ohm taps. Edcor doesn't show it on their webside, but you can order it for the same price as the one shown. The downside is that the OT has exposed solder terminals which is inherently unsafe. You never want B+ exposed outside the chassis. Edcor won't make it with flying leads anymore. As such I wouldn't recommend it for beginners, which is too bad, the price is right.

Edit: having said all that, I've got two V3 VJs that I am going to leave stock. I plan on running a stereo multiFX unit of some kind into them. The only tweak I plan on doing to the stock units is to replace the 12AX7s with a 5751 preamp tubes. The 5751 is like a lower gain version of the 12AX7. Hopefully this will give the amp more clean headroom.

tung

[luvmyshiner]

I have no idea what you guys are talking about. But I like it!

[just strum]

I have no idea what you guys are talking about. But I like it!

I'm glad I'm not alone with that. That's the advantage with acoustic - bridge, saddle, nut, soundhole, truss rod. You know that and 95% of what you need to know is done.

[sumitomo]

Hey guys my VJ Head just came today,Ive been looking at your websites to long to let you guys have all the fun.Also both of you have done a great job with your info.So Ill play it for a week and then break out the soldering iron.Sumi

[duhvoodooman***]

Warren0728 asked elsewhere about the possibility of dropping the power on a Valve Jr from the stock 5W down to 1W or so. I thought the response really belonged here in the Mods forum, so am tacking it on to this thread.

Interesting question. Since it's only 5W to begin with, most people are interested in mods that add MORE gain or output to the VJr, rather than less. But since even 5W can be deafeningly loud in a small area, this power reduction could be very useful to the home player.

Several large amps that let you drop the output substantially do this by "subtracting" power tubes from the circuit. The Mesa Lone Star series amps are a good example of this approach. They have 4 power tubes, but give you the ability to run with only one or two of them, dropping the output wattage accordingly. But since the Valve Jr. only has a single tube to begin with, this is obviously not an option. Zero power tubes is a little too quiet!

Some of the potentially useful power reduction options would include the following:

1) Add the capability to switch the EL84 power tube from pentode to triode mode. Not sure exactly what would be involved as far as the actual circuit modification, but this is a stock feature on the newer Blackheart Little Giant amps. But this only drops the output from 5W to 3W, which really doesn't make that big a volume impact. It also changes the tone somewhat, though not in a bad way--just different. But to truly quiet the amp and let you push the preamp & power stages at "bedroom" volume levels, I don't think this approach is gonna get you there.

2) You could conceivably convert to some lower output power tube type. Not sure what that would be, since the stock EL84 is already at the low end of commonly used power tubes. But there are certainly a boatload of more exotic tube types, and I have to believe there would be something useable available in the 1W range, though some type of adapter might be needed to make it pin-compatible with the VJr power tube socket. The downside with this approach is that the tone would almost undoubtedly be affected. Plus, the EL84 output tube is an integral part of the characteristic VJr tone. I really don't see a 1W tube getting close to duplicating that sound.

3) A well-known modification for the VJr is the installation of a "master volume" pot between the preamp & power stages. This would be a kind of "halfway" solution, as it would allow you to run the preamp gain up high to generate some crunch there, but would allow you to keep the actual output volume down. The problem with this approach (as with any master volume type amp) is that you don't get that nice creamy power tube saturation until the master volume is also dialed up, and that's the distortion that most folks think sounds the best. But this is certainly a partial solution to the volume issue, and one that is quite easily & cheaply done.

4) I think the best overall solution for getting the good saturated tone for which the VJr is known & loved at low volume levels doesn't involve modifying the amp at all. My recommendation would be to look into a good low-wattage attenuator, like the Weber MiniMASS or MicroMASS. These units are quite reasonably priced ($70 - $75), are very well made, and have a reputation for altering an amp's tone very little. So you can maintain the VJr's fundamental tonal character, drive the preamp and power stages to saturation, and still keep the final volume level at very manageable levels. Sure, the cost is more with this approach, but you also end up with a stand-alone attenuator that you can use on other low-wattage amps.

There may be other viable approaches to this issue, though, so I invite anybody else to chime in here....

[tjcurtin1]

I think that there's a youtube video of someone playing the valve jr with a webber attenuator...

[warren0728]

thanks for the comprehensive explanation vood...i had a feeling that would be the case!

ww

[Ch0jin]

I think that there's a youtube video of someone playing the valve jr with a webber attenuator...

And here it is...http://www.youtube.com/watch?v=sK5dzFwbfS8


I HIGHLY recommend checking out the rest of this guys videos, or if ur strapped for time, just watch the ones where he uses a modded Plexi. Man that thing is sweet.

But anyway, yeah from what I've read and listened to regarding EVJ's I suspect an attentuator is the answer for lower volume. Anything else really makes it a different amp completely tone wise.

[duhvoodooman***]

I've been on the lookout for a decent deal on a used Weber MicroMASS attenuator on eBay for awhile now. They don't come up very often, and seem to go for almost the retail price when they do, so I may have to break down and just buy one from Weber.

Even at 5W, to get that really nice tube saturation sound, the VJr is too loud in the small room where I generally play. From what I read, these little Weber attenuators work great and introduce very little tonal coloration of their own. At $70, the MicroMASS is very reasonably priced for a high quality speaker motor-type attenuator. And I can use it with my Blues Junior or Firefly, too, if I want to.

[Ch0jin]

Here u go....just $9.99 at the moment

http://cgi.ebay.com.au/WEBER-MICRO-M...dZp1638Q2em122

[vroomery]

I'm talking about building one from scratch. It might be more cost effective to buy a head and replace it with a complete board.

[tunghaichuan***]

I'm talking about building one from scratch. It might be more cost effective to buy a head and replace it with a complete board.

Before I owned any of the VJ amps, I built one from scratch just to see if I could do it. It came out great and sounds better than a stock VJ. I'd been collecting parts for a long time before, so I doubt I have more than $50 in it, but if you were to buy all new parts, it would no doubt cost more than a VJ amp. I would buy a used amp to further increase your savings.

[Commodore 64***]

Wait, that's' a Vox/Fender version..it has an Orange Drop AND a Mallory! Are you sure it won't explode or something? What if the Orange Drop goes for Declaration of Independence?