JB Blues
1 post
Jan 28, 2020
9:05 AM
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Hi, I'm trying to modify a Fender Blues Jnr3 for harp. I intend to swap the V2 & V3 valves for 12AU7s - I'm on a budget so does it matter a huge amount which 12AU7s I use? I also read that snipping off the C3 cap would help my tone - is this correct? And I've heard that Billm mods would be good - what are they and do they work? All help on this subject appreciated.
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BnT
257 posts
Jan 28, 2020
9:48 AM
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You're headed in the right direction. You can't do too much mod wise because it's a pre-printed circuit board (and I'm not familiar with the Billm mod). Replacing the AX 7's should cut bass and pop and help with feedback, but consider the options (some manufacturer's are slightly different)
12AX7 - 100% gain
12AT7 - 60% gain
12AY7 - 45% gain
12AV7 - 41% gain
12AU7 - 19% gain
So, you may want to cut the gain from 100% but maybe you want a little more oomph (gain) than 19% x 2. Maybe a Y and a U or T and U. In my Bassman I replaced the X's with Y, U, T. I prefer NOS tubes but financially, see what you can find. I'm not a fan of Chinese tubes but Sovtek and Electro-Harmonix might be okay.
You're right about the C3 cap. You're probably already aware that unlike Fender amps with a bright switch (and the option to turn it on/off), the Blues Jr. is wired so bright is always on. Disconnecting C3 will turn off the bright mode. Just snip one end so it's not connected to the board. That will cut the thin/bright tone.
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BnT
www.BluesWithAFeelin.com
Last Edited by BnT on Jan 28, 2020 10:20 AM
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gmacleod15
328 posts
Jan 29, 2020
4:20 AM
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This topic has come up on the forum before.
I had a BJr and tried the tube swap and disconnected C3 and put a nice Weber speaker in it. All those things helped but in the end it still was not a very good harp amp in my opinion. I sent it on its way to a guitar player. The tube swap is cheap and easy...try the 12ATZ. It may work for your needs.
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MBH member since 2009-03-24
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dougharps
2057 posts
Jan 29, 2020
7:40 AM
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I have a friend who plays harp through a Blues Junior who substituted using an Ecc832 (aka 12dw7) as discussed in the thread below.
MBH tube swap thread
I played through it with an old CM JT30, and it sounded pretty decent, better than a regular Blues Junior.
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Doug S.
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harpdaddy
17 posts
Feb 02, 2020
11:59 AM
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Check out bilmaudio.com for his mods and great advice on tubes, etc. I have a 1998 model that I have done a bunch of his mods on. I also removed the bright cap. To my mind the biggest improvement was replacing the out put transformer with a Mercury Magnetics Blues Junior specific one. Bigger bass and less of a boxy sound. Tried tube swaps and 12AU's sound dull in any slot to me. There really is no reason to change out the 12AX in slot 2 because only half of that tube is used and only to recover signal lost from the preamp. I actually run mine with the master volume turned all the way up and use the volume to adjust the volume. This way you are pushing the power tubes harder and you have less preamp distortion.
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