Some MAJOR work planned for my Blues Junior....

[duhvoodooman***]

A couple of years back, I did a couple of the "BillM" mods to my Fender Blues Junior amp, as described HERE. I've been pretty happy with the sound of the amp, especially since changing to an Eminence Cannabis Rex speaker a couple of months back. That smoothed out some treble harshness that I was hearing with brighter guitars. But you guys know me--what's good can always be made even better!

I'd been looking at Bill "BillM" Machrone's new Blues Junior website a few months back and I saw he'd added a bunch of new Blues Jr. mods--some to further improve tone, some to improve the usability of the controls, and some to add features that this fairly low-priced tube amp lacks. Not only that, but he now sells kits for most of these mods at very reasonable prices, with all the parts you need and detailed instructions for the installation. So today, I bit the bullet and ordered a whole bunch of them. Here's the list of the nine (!) mod kits I ordered:

• Audio taper volume pot
• Audio taper reverb control
• All-metal Switchcraft input jack
• Aux. speaker jack
• Line out jack
• Standby switch
• Presence control
• 22W Heyboer output transformer with 4/8 ohm switching
• Octal tube conversion

Many of these are very fast and easy, though a couple are definitely more involved, particularly the octal tube conversion. I'll probably try to work in the mods piecemeal between customer pedal builds, so they may take a while to complete. I haven't done any amp work in quite a while, so this will be a good warm-up for that Trinity Amps 18W kit that I STILL haven't started building! (hangs head in shame)

Additionally, I'll be doing a 10th mod that doesn't require a kit--wiring in the unused half of the V2 preamp tube as a cathode follower between the preamp and the tone stack (see link for the benefits this offers). I'll also be changing the existing 12AX7 tube at V2 to a 12DW7, since the purpose of the cathode follower is to provide current gain, not voltage amplification. The 12DW7 is a "hybrid" tube--a 12AX7 type triode on one side and a 12AU7 triode on the other. Since the AX7 is a voltage gain triode and the AU7 is an excellent current driver, it's ideal for this application. And I just happen to have one on hand!

While all the mods have their individual benefits, I'm really looking forward to hearing what comes from the combination of the Heyboer OT and the octal tube conversion. The amp is said to take on much more of a Fender "Blackface" character with these mods--taut, round lows and a brighter, glassier top end. I've also ordered three sets of octal output tubes to try in the amp: matched pairs of JJ 6V6-S's, Tung-Sol 6V6-GT's and Tung-Sol 5881 Reissues. Machrone has tested 5881's in this modification and reports that the amp will drive them very nicely, and they'll break up earlier than the 6V6's. Plus, the output of the amp jumps up to about 25W from the stock 15W! Should be fun to try 'em all and see which set sounds the best.

The only down side to this is I'm going to end up with about the world's most expensive Blues Junior when I get done. If I ever decide to sell it, I'm quite sure I won't be able to get back out of it what I will have invested. But that's not the point--this is all about tone and flexibility, not economics! Plus I'm tentatively planning to have it buried with me....

[mainestratman]

Awesome deal.

My biggest complaint about Fender amps is that they go from quiet to FRIGGIN LOUD when dialing from 0 to 1 or so. Do the taper pots fix that? I would love very much to replace the pot on my clean channel, at least...

[marnold***]

Sweet! Keep us posted.

[duhvoodooman***]

My biggest complaint about Fender amps is that they go from quiet to FRIGGIN LOUD when dialing from 0 to 1 or so. Do the taper pots fix that?

Yes, that's exactly the purpose of switching to the audio taper pots. The Master Volume control isn't the only one with this issue--the Reverb control on the Blues Jr. acts much the same way--very difficult to get fine control at lower levels.

[mainestratman]

Thanks DVM. I'd been reading about taper pots and got myself all confused.

I know what my next project is. Hope I don't kill the amph. :-)

[bcdon***]

Thanks DVM. I'd been reading about taper pots and got myself all confused.

If you think you're confused, I thought this was a tapir!

[markb]

Yes, that's exactly the purpose of switching to the audio taper pots. The Master Volume control isn't the only one with this issue--the Reverb control on the Blues Jr. acts much the same way--very difficult to get fine control at lower levels.

I never found the volume pot taper problem on either my Pro Junior or Blues Junior. They were both frigging loud though as stated above.

The main problem I had with the reverb on the BJ was just the way it sounded. I used to use a nice sounding Ibanez Soundtank DL5 for "hard reverb".

[tunghaichuan***]

Looks like some cool mods coming your way. I'd be very interested to see what you come up with.

[guitartango]

Looks like a lot of work to me, what is the quickest mod ? Speaker change or change the tubes ?

[markb]

Looks like a lot of work to me, what is the quickest mod ? Speaker change or change the tubes ?

Valves are much quicker to change than the speaker. You still have to take the back panel off the BJ though iirc.

[duhvoodooman***]

Looks like a lot of work to me....

Yeah, but that's the point. This stuff is fun to do!

[mainestratman]

DVM.. you done yet? Clips? :-D

[duhvoodooman***]

WHEW!!! That was a lot of work! I dove into this project on Friday evening and worked on it off and on all weekend. Just a LOT of stuff to do to finish these 10 mods, but I figured I might as well go whole hog as long as I was taking the amp apart. Plus, since I don't do much amp work, I took it very slowly and triple checked everything step by step. Finally got it back together late last night, but couldn't play it since everybody was in bed by the time I finished (I hate it when that happens!).

So I did get a chance to BRIEFLY try it this morning before work, and--WOO HOO!!--everything worked the first time. I have a pair of Tung-Sol 6V6-GT's in the amp right now, and it sounds very good--gives it more of a Blackface character now, and it's definitely got a deeper & tauter sounding bass. I've also got a pair of JJ 6V6-S tubes to try in it (kind of a "6V6 on steroids" tube), as well as a pair of Tung-Sol 5881 Reissues that are reported to give the amp some serious authority, and raise the output to near 25W! Looking forward to giving both of those a try.

The cathode follower mod and the octal tube conversion were by far the most involved of the modifications. The octal conversion was especially nerve-wracking, since it involved cutting off the end of the tube-mounting circuit board with the two EL84 nonal sockets. No going back, once that was done! But slow & careful carried the day and everything seems to function perfectly. I'll try to post some photos, though it will probably be a few days before I can get a clip posted....

[Bloozcat]

WHEW!!! That was a lot of work! I dove into this project on Friday evening and worked on it off and on all weekend. Just a LOT of stuff to do to finish these 10 mods, but I figured I might as well go whole hog as long as I was taking the amp apart. Plus, since I don't do much amp work, I took it very slowly and triple checked everything step by step. Finally got it back together late last night, but couldn't play it since everybody was in bed by the time I finished (I hate it when that happens!).

So I did get a chance to BRIEFLY try it this morning before work, and--WOO HOO!!--everything worked the first time. I have a pair of Tung-Sol 6V6-GT's in the amp right now, and it sounds very good--gives it more of a Blackface character now, and it's definitely got a deeper & tauter sounding bass. I've also got a pair of JJ 6V6-S tubes to try in it (kind of a "6V6 on steroids" tube), as well as a pair of Tung-Sol 5881 Reissues that are reported to give the amp some serious authority, and raise the output to near 25W! Looking forward to giving both of those a try.

The cathode follower mod and the octal tube conversion were by far the most involved of the modifications. The octal conversion was especially nerve-wracking, since it involved cutting off the end of the tube-mounting circuit board with the two EL84 nonal sockets. No going back, once that was done! But slow & careful carried the day and everything seems to function perfectly. I'll try to post some photos, though it will probably be a few days before I can get a clip posted....

Only you thought the outcome was in doubt. We all knew you'd prevail...

[duhvoodooman***]

Some photos (edited to add descriptions):

Rear shot of the amp, angled to show modifications to the top panel components. From left to right, here's the new 3-position off-standby-on toggle switch, new audio taper reverb and master volume pots, then skip over the next three stock control pots to the new Presence control, another stock pot, and then the new all-metal input jack (isolated & shielded coax cable). The Presence control pot also has a push-pull switch on it for BillM's "clean boost" mod, but I didn't do that one, since I have several boost pedals.

Another rear shot, but angled down to show the tube sockets and output jacks. The green tube PCB at the lower right used to extend across where the white ceramic octal sockets are now installed, with the pair of EL84 output tubes mounted in nonal sockets attached to the board. That portion of the board was physically cut off and the two octal sockets mounted rirectly to the underside of the bottom of the chassis and wired in to the main board. At far left are the two new output jacks--a line-out and an auxiliary speaker jack. Moving right, it's the stock footswitch and main speaker jacks, and then the new 4/8 ohm impedance switch for the Heyboer TO22 output transformer (not visible mounted to the other side of the chassis, behind the main PCB).

Here's a shot of the top of the control panel. In addition to the small knob for the new Presence control between the Treble and Volume pots, take note of the settings of the Reverb and Master Volume controls on the left side. With the old linear taper pots, those would usually be turned down around 3. Now they're typically running up around their mid-points--the sensitivity is significantly lessened and thus they are much more usable.

Just a close-up of the output section showing the new line-out and aux. speaker jacks, as well as the 4/8 ohm output impedance toggle.

Here's a close-up of the new octal socket installation. The green and brown wires connected to pins 2 and 7 on each socket are the filament heater voltage supplies, and the black wires connect the various output tube elements to the main PCB. With the old EL84 output stage, these connections were made with the same flat, grey ribbon cables that you can still see connecting the preamp tubes on the green tube board in the previous photos.

A close-up of the tubes, showing a pair of JJ 6V6-S output tubes in the new octal sockets. The middle preamp tube (V2) is no longer a 12AX7, but rather a JJ ECC832 (a.k.a. 12DW7), installed as part of the cathode follower mod. This mod allows the unused half of V2 to be inserted between the V1A preamp tube output and the tone stack, where it can more efficiently drive the stack. The 12DW7 tube is used because it's a hybrid construction--of the two triodes it contains, one is a 12AX7 type, but the other is a 12AU7 type. That triode design has very low voltage gain (less than a fifth of the typical 12AX7), but is great for supplying a lot of current--just what the cathode follower is designed to do.

This last shot is another close-up of the tubes, but here I've substituted a pair of Tung-Sol 5881 Reissues for the output tubes. This tube basically falls in between the 6V6 and its big brother, the 6L6. With the 5881's installed, the Blues Junior's power is increased to about 25W from the stock amp's 15W output. While I don't need the extra top-end volume, what I do really like about these "big bottles" is the added bass punch. To borrow a line from Bull Durham, they "announce their presence with authority."

[Tone2TheBone]

Bob, how do these mods sound in the stock cabinet? Is there a noticeable difference in overall tone? Do the mods push the envelope of the limitations due to that small cabinet? That's a lot of work you've done I would hope it does surpass the cab's limits!

[otaypanky***]

there's a guy on eBay who sells Hot Rod Deluxe sized finger jointed pine cabinets for a Jr, about $150 or $165

[ZMAN]

I am not into modding, so I just bought a 65 Deluxe reverb.
Now I have two amps for probably what you have in your BJ. LOL

[Matt]

DVM, have all these mods made the amp get over its boxy nature at louder volumes? I still havn't got round to doing the BillM mods yet and now after buying my Blackstar I'm having a hard time justifying it and not just getting rid of the Blues Jr. But at the same time, it would be cool to run them in stereo...