Pro JR

[skylabfilmpop]

I need a good practice amp. The bluse juniors sound terrible b ut these sound nice but are too loud. Anyone ever pu a PPIMV on these with sucess?

[TheAmpNerd]

I need a good practice amp. The bluse juniors sound terrible b ut these sound nice but are too loud. Anyone ever pu a PPIMV on these with sucess?
What a pain in the ass. Probably not worth the money to do it.

These amps have that brittle high end that goes right into my
head and gives me a head ache when ever I hear them.

They are okay for folks who can't hear and have attenuated high end
hearing loss....

[skylabfilmpop]

I am talking about the Pro Junior, not the blues junior and I am takling about a practice amp, it doesn't have to be a Dumble. Pro Jr's sound pretty good, I personally know a few really high profile players and producers who own/use this amp. Is there a circuit revision or speaker issue I should be aware of? A friends of mine tweed one sounds fine, organic and bassman like. I bet they started putting ceramic speakers in them instead of the alnico jensen they had before. Thanks for your .o2 ampnerd but its just a practice amp. I want somthing cheap that I can drag out on to the deck and play a bid, not worry about getting dirty or dusty.

[John Phillips]

Yes, you're quite right that the early ones had Alnico speakers and the newer ones have ceramic. It may have been changed at the same time as they went from Tweed to black, I'm not sure. The Tweed ones do sound very good - I know for certain that Neil Finn records and tours with one, I've seen him using it. I think there's another change when they went from US to Mexican manufacture too. (Not a knock on Mexico or Mexicans, but they did change some things in the amp too. In fact, the Mexican Blues Junior sounds better than the American one, to me.)


Fitting a simple cross-line PPIMV should be very easy. The biggest problem is where to put the pot. I'd be inclined to drill the underside of the chassis - it will be more of a pain to reach, but not mess up the appearance of the amp.

What you need is one of those 250K No-Load pots that Fender use as guitar tone controls - you should be able to get one from any Fender dealer. They work ideally as PPIMV controls because they are out of the circuit when turned fully up, so the amp is then totally stock. You can chose plain or split shaft depending on what type of knob you need to use.

Next, locate the two power tube grid feed points - not on the tubes themselves, but upstream of the grid stopper resistors. These points should be on the small tube board, but I can't remember exactly where, sorry. Follow the circuit back from the power tube pin 2, go through the resistor, and the place you want is on the end of the resistor away from the power tube (one per tube). Connect these two points to the CCW and center tags of your No-Load pot. (The CW terminal is not used, and there should be no ground connection to the pot.)

That's it :).

If all that sounds like Greek to you, or you're not familiar with this sort of work, find a tech to do it - it should be less than an hour's work including drilling the chassis and testing it. You shouldn't have to dismantle the amp further than just taking the chassis out.

This type of PPIMV isn't 'the best', and it can sound a bit scratchy or harsh at lower settings, but it is certainly the easiest and least invasive to fit, and works well enough IMO.

[Mike T]

I'll tell you what, I've got a Blues Jr that I lowered the bias on, put a couple larger caps in the tone stack and put a cathode follower in the spare triode. I also put a Vintage 30 and some Mercury Magnetics transformers in it and now it is my main gigging amp. I use it with a 1x12 extension using the 4ohm tap on the OT. This may be a bit much for you, but I just had to respond when you said the Blues Jr sucks. Of course the reverb still sucks, but I use digital in front of it anyway.

[skylabfilmpop]

Right Sorry to offend My comment was in the context of "out of the box", not after having been significantly modded, which sounds like a cool resourceful few mods youve done to yours, share your sources if possible. a lot of the BJ mods i have seen have actually involved making the circuit more like a a PJ which leads me to believe the PJ may be better sounding to begin with.

[Mike T]

Right Sorry to offend My comment was in the context of "out of the box", not after having been significantly modded, which sounds like a cool resourceful few mods youve done to yours, share your sources if possible. a lot of the BJ mods i have seen have actually involved making the circuit more like a a PJ which leads me to believe the PJ may be better sounding to begin with.

No offense taken, man! I was just defending the lowly Blues Jr. :) I got the mods off the web. I just googled "Blues Jr mods" and there were a lot. The ones I used were from home.comcast.net/~machrone/bluesjunior.htm
and mhuss.com/BluesJr/index.html. Dave Stork has some good ideas too. Increasing the plate resisters on the first couple 12ax7 gain stages from 100K to 150K definately adds some dirt. The cathode follower was just icing. The first I played through one I thought it was thin. I found a used one in perfect shape for $200 so I bought it and did some mods. The most significant ones were lowering the bias and the bigger caps is the tone stack and swap out the speaker. It sounded so much better. I first tried a Celestion Lead 70 and it sounded bad. A Vintage 30 took care of that. Now I have a Celsestion G12H-80 and it sounds great. I also have 2 Pro Jrs but I gave them to my daughters. Maybe I should try and get them back! I don't think the circuits are that much different except for the reverb and the mid control. I can't remember if the Pro jr has a master.

[Backstage Kent]

The "Bill M" mods, often discussed over on the FDP, do wonders for the Blues Jr.. I personally don't bother with separate bias controls for each tube. Making the bias adjustable, adding 1 ohm resistors to the EL84 cathodes and tweaking the tone stack takes about an hour for an experienced tech. After these mods most people are happy with the stock speaker, although one of my more recent ones swapped in a Jensen C12K and said it increased his clean volume--haven't heard it myself.