Re: [Harp-L] Fender Blues Jr-NOS

[Mojo Red <harplicks@xxxxxxxxx>]

Hi, 

You won't screw up your amp by replacing the pre amp tubes with tubes of various gain levels, but you will discover some differences in how the amp sounds, and how much oomph it has. Lower gain tubes boost the signal less than higher gain tubes. The higher the gain on that signal, the more oomph... but the more oomph, the more feedback-sensitive it will be. At least that's been my experience with the Blues Junior. 

Scott made some great observations on how differnt tubes also have a different "voice", but I'm mostly deaf to those subtleties. That being said, I went ahead and re-tubed my BJ a number of years ago (pre-amp and power tubes). I went with tubes from JJ Electronics, choosing matched power tubes and a variety of pre-amp tubes that I mix and match, depending on how gear-headed I'm feeling at any moment. 

Mostly I have gone with this set-up: a 12AX7 in the phase-inverter slot (the slot closest to the power tubes), a 12AY7 in the midle and 12AU7 in the slot farthest from the tubes, but you can swap those around any which way and get varying "voices". Recently I learned about a dual-gain pre-amp tube called 12DW7 that you can use in that first position (phase inverter slot, closest to the tubes) that's supposed to fatten up tone without adding too much feed-back. I guess half the tube is set at one gain factor and half set at another (I really don't understand this stuff too deeply). I've used it and it does seem to offer some benefits of more power without sacrificing fat tone.

I've been very happy with the JJ EL84 power tubes. Overall, this lowered the edginess and added some warmth to the amp. 

You can pick up JJ tubes (and learn about them) at Eurotubes:  
http://www.eurotubes.com  

The tubes from JJ use European designations, so they will carry different names.
EL84 = 6BQ5, but US designations are listed with each product so it's easy to find what you need. 

With all that said, however, the best investment I ever made into my BJ amp was swapping out the stock Eminence speaker for a Weber vintage-made speaker with AlNiCo magnet. However, yours sounds like it's aready cooking with a vintage Jensen, so you're likely already quite well set up in the speaker department.

Hope this helps.

Harpin in Colorado,
--Ken M.


----- Original Message ----
From: "gmmsi@xxxxxxxxx" <gmmsi@xxxxxxxxx>
To: harp-l@xxxxxxxxxx
Sent: Wednesday, March 12, 2008 1:26:55 PM
Subject: [Harp-L] Fender Blues Jr-NOS

I have recently acquired a Fender Blues Jr NOS (tweed with Jensen speaker)--hoping to use it for harp and guitar

To improve it for harp I understand I should change the pre amp tubes--the current 12AX7 tubes have a gain factor of 100

A 12AY7 has a gain factor of 45---is that the tube to go with?

I still hope to be able to swap back and forth for guitar/harp--so there is a 70 gain factor tube (5751)

I don't want to screw up the amp
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