Hi,
I play a lot of Dead music and I do so with a Blues Junior. I'm kind of a tone fanatic and have done many modifications to my guitars, effects and amps. To get the Blues Junior to provide decent tone, I had to replace the first tube in the pre-amp with a New Old Stock Telefunken tube. I think pretty much any New Old Stock tube would be an improvement. Although I have experimented with vintage tubes in all positions in the amp, I found I liked it best with stock tubes in all positions except the first pre-amp tube (V1).
I also replaced the stock speaker with an Alnico Tone Tubby (famous for their use of hemp cones). In order to get it to fit, it is necessary to remove the "bell" on the back of the speaker. There is a screw under the label, in the center, that holds it on. This is the same speaker used by Clapton and Santana. It helps to remove the shrillness from the Blues Junior.
Another trick with the Blues Junior is to dial the treble knob way back. I keep mine at around 2. I have the Mids and Bass at around 7, but I am playing a strat through it(think Europe 72), so these settings may be too boomy for a humbucker equipped guitar.
My other amps are a 1954 Fender Champ, an all-tube Marshall DSL401, and a 1971 Silvertone Amp that I refurbished myself. Of all of these Amps, it's the Blues Junior that works the best for Dead tunes.
The modifications I described will run you about 275$. Its 250$ for the Tone Tubby and about 25$ for the NOS tube. From your perspective, I would guess it seen a risk to spend that much cash to spruce up the Blues Junior... but it certainly worked out well for me.
Regardless of what you decide, I wish you luck in your quest for the perfect tone!






