I have an early 70's Pro Reverb that I "Blackfaced." I turned the Master Volume into an adjustable Negative Feedback.
I have a Weber 12F150 and a 12F150B, lightly doped (like most of my friends) and 25watts each. These speakers have so much sparkle and chime that I forget to play my Mesa's sometimes. Plus, you can get them pre-broken in now.
This amp gets me some serious Blues tone with no effort. I don't even touch the knobs sometimes, my 2 year old plays with them and I just plug in. I make sure the Volume is down a bit, but I leave the others alone to see what tones are available. Otherwise I find myself going back to the same settings.
No matter where the knobs are, it just sounds great.
You can still get some Silverface amps for cheap. It won't get you that exact tone, but very close. I find that a lot of the tone is in the fingers too. I've seen really great players never even touch their amps, just the Volume and Pickup Selector on the guitar and pull many different tones out of the same axe with the same amp. I'm always amazed by this.
There is a guy, Bill M on the Fender Forum that has a website dedicated to modifying the Blues Jr. Lots of people are really happy with the mods.
I guess my point is, like fdeslvo said, you may need another amp to get this tone.
I use my DC-2 and a good pedal sometimes to get some serious bluesy tones, but still not the same. I have replaced the Clean Channel Tone Stack with film capacitors, Output Transformer (original was shot) with a Mojotone Heyboer Deluxe Reverb upgrade, and the speaker is now an English made (not Chinese) Celestion Heritage 30. Lots of great sparkle with single coils.