Amp mod report (with major Pryde shout-out!)

[Bret608]

Hi all,

So, this is what I've been working on lately. My trusty ol' Blues Jr. was having some heat and popping issues last fall, no big surprise after 18 years with no mods or service, I guess! So, I retubed it in the fall, and over the last month took on modding and recapping it as well. Forum member Pryde was a big help, fielding lots of questions from me as I worked through this. I hope he knows how much I appreciate it! I did the Bill M basic mods, and replaced the remaining filter caps with some nice F&Ts that I ordered from Tube Depot.

Sound-wise, it's a huge improvement. I'd describe it as a Princeton Reverb killer. The work was a little nerve-wracking due to the thin board and ribbon cable, but I have a pretty light touch with wires and soldering irons in general. My younger daughter snapped these pics--we had a hard time getting them to not blur, but oh well! I tried to use some hot glue to insulate the larger caps from vibration as Bill M suggests. Not beautiful on my part, but overall I'm really proud of this for a first foray into working on amps. Pedal building had me well-prepared to take it on.    I'm sure I could dress that ribbon cable a little better, and maybe retention the tube sockets at some point. But for now I am merrily rocking out.

[Stomptown]

Great job! I haven't jumped into amplifiers yet but this is giving me the big. Maybe I shouldn't have sold my 20 year old Deville!

[jkokura]

If I keep saying it, it will happen.

I will build an amp this year.

Also, great work Stompy. I think the Blues Jr is a great amp

Jacob

[Bret608]

I'm glad to pass that bug along, Jon! It was a cool feeling powering it up after the mods. Thanks for the kind words.

I agree Jacob, I already loved my Blues Jr. But I have to admit I was surprised at how different it sounds now. For starters, the reverb is actually useable. Also, the cooler bias makes it sound way less hissy and over-compressed. When I'm in the both pickups (humbucking) mode on my Mustang, it's so quiet you'd think the amp isn't on. The bass and mid pots behave quite differently. The bass is both tighter but also bigger-sounding.

Before the mods, I had put a 12ay7 in V1 to try for more headroom and less noise. I may try something a touch higher gain again like a 5751, but it is really pedal-friendly so I'm not sweating it.

[jkokura]

I think I'm going to get a few new Tubes to try in my Tweaker. I like it with the stock Chinese ones in there, but trying out new types is something I have no experience with. Dropping a 12AY7 in V1 is supposed to change your life.

Jacob

[pryde]

As I said in our PM's: Awesome work!

Glad I could answer your questions along the way but make no mistake it was all you so take full credit for your hard work. The improved amp should give you years of good service with those nice F&T caps and correct tube biasing.

I have a couple builds slowly in the works: a matchless spitfire and a modded 5F2a that I hope to have up and running within a couple months. Love amp building and know there are a lot of skilled amp gurus here on MB.

[Bret608]

Much appreciated, Jeff! Full credit taken... 

That Spitfire sounds awesome...I'm itching to build an amp for sure but will likely just goof around with this one for a bit more, maybe trying a new OT or speaker. Forgot to mention, swapped out the input jack for a Switchcraft with shielded cable as well (pre-wired from Bill M). Apparently, on the green board version, the on-board stock jack is on a hum-prone part of the board. Bill has you bypass all that and solder straight to the input and grid resistors. Huge improvement.

Jacob, you may have just as much fun with some different 12ax7s. 12ay7s have half the gain, so those could change your life for the better or worse I guess, depending on what you're going for. I totally jacked my idea for the V1, 2 and 3 combo from Torres Engineering's "Blues Forever" tube set.

[Rockhorst]

Great to see/hear all went well with this! Looking good. You should've done some before and after recordings :p

[pryde]

Much appreciated, Jeff! Full credit taken... 

That Spitfire sounds awesome...I'm itching to build an amp for sure but will likely just goof around with this one for a bit more, maybe trying a new OT or speaker. Forgot to mention, swapped out the input jack for a Switchcraft with shielded cable as well (pre-wired from Bill M). Apparently, on the green board version, the on-board stock jack is on a hum-prone part of the board. Bill has you bypass all that and solder straight to the input and grid resistors. Huge improvement.

Jacob, you may have just as much fun with some different 12ax7s. 12ay7s have half the gain, so those could change your life for the better or worse I guess, depending on what you're going for. I totally jacked my idea for the V1, 2 and 3 combo from Torres Engineering's "Blues Forever" tube set.

You bet those crappy input jacks always need yanked out and replaced. Another thing if you didn't do it already is to re-flow the power tube pins on that pcb. Those are notorious for going cold and cracking on that amp. Its a "when not if" kind of thing. Easy preventive thing to do without having to remove anything except the back panel.

Time for a sound demo 

[Bret608]

Thanks Rutger! That reminds me, now I can set my brain free to figure out which of your PCBs to order...

Jeff, I am definitely going to reflow those socket pins on the power tubes. I just read up on that yesterday actually. Just seems like added insurance considering the amp has been running with that hot bias all these years. It's just ridiculous how cool the back of the amp feels with the new bias adjustment compared to before. My kids used to be scared to touch it!

How easy is re-tensioning the tube sockets by the way? They still feel good and tight but that also seems like a no-brainer for long term maintenance.

[pryde]

I have always just used a fine dental pic with gentle pressure. You will see the little gap close a bit and that's it.

Before you do that though spray the pins on one of your tubes with deoxit and plug/unplug a few times in each socket. Then tension the pins and your good to go. Actually do all this before you reflow the solder joints so you don't stress the new flowed solder.

[Bret608]

That makes total sense--I'll see if I can borrow a can of deoxit from the electronics folks where I work.

[Gledison]

BAh! this looks great! one day i will give it a try on amps...in a near future..
u should definately be proud!
Cheers

[bcalla]

I'm Impressed, nice work.

I have a Blues Jr. and love it.  I have browsed around Bill M's site but could never decide what to do - he has so many options.  Did you just do the Basic Kit?  Or did you change anything else while you were in there?

[gordo]

Nicely done.  The nice part about BillM mods are that they make a noticeable improvement and are fairly easy.  For newbies it's pretty nerve-racking to take the board out of a Junior and the boards are cheezey enough that you don't want to make a habit of it.  But they're fairly simple amps and fun to goof with.  By the time you're done it's like you said "a Princeton killer".  Plus you BillM's stuff is so reasonably priced that you don't mind flipped him a few extra bucks for all his work.

One of the kids in the praise band I play in picked up a very nice Jr. but was in really bad shape and I spent a bunch of time getting it running.  Other than stiffening up the power supply a bit it was a great sounding amp so I left it pretty much stock.  Was too cool to have him tell me my guitar sound killed and see the look on his face when I told him it was his amp I'd been playing.