Tubes for Fender Blues Jr. Tweed

Alvin Douglas · Post by **Alvin Douglas** » 13 Jun 2014 8:31 am

Hello All,
My Fender Blues Jr. has been making some odd sounds lately so I decided to tap test the tubes. The tube in the pre amp position (extreme right looking at the back) would transmit a tap to the speaker. I did the tests with the amp's volume settings on 12 and nothing plugged into it. So I removed all 3 of the 12AX7 tubes to find that 2 were actually 12AX7A and the pre amp position tube was ECC83.S. I bought the amp new and this is the first time it has been apart so I am confident this is how Fender tubed it. Any intel appreciated.
Alvin

Dennis Russell · Post by **Dennis Russell** » 13 Jun 2014 8:56 am

You can find out everything you need to know about Blues Jrs and a bunch more that is good to know at http://billmaudio.com.

He has several pages of mods as well as suggestions of what type of preamp tube to use (whether high gain or low gain) to change the tone of your amp.

There's lots of info on that site. It'll keep you busy for days. Have fun.

Jerry Hedge · Post by **Jerry Hedge** » 13 Jun 2014 7:09 pm

Alvin, a 12AX7 and a 12AX7A are the same tube. ECC83 is the European name for the same tube. Most of the time the first preamp tube will transmit a sound if it is tapped, especially at full volume (volume knob at 12). I would suspect that it's the output tubes (EL84's)that need replacing. They EAT output tubes!!!That amp was designed to bias the outputs VERY HOT!!!(for a big amp Rock or Blues tone.) One of the Bill M mods is an adjustable bias control to lower the bias voltage. You might want to try a new set of output tubes. If you can find them, try a set of new old stock 6BQ5's That's the American equivalent for the EL 84's.

Alvin Douglas · Post by **Alvin Douglas** » 15 Jun 2014 12:25 am

Thanks Dennis and Jerry. I put the tubes back in their original locations for now. It does make a great tone with a tele. The amp is about 3 years old and has lots of hours although not at real intense volumes so you are probably right, a new set of O/P tubes would not hurt. I did find lots to read about on the BillM site and may decide to send it to him to be mod'ed once I return to the USA. Thanks again for your help.
A

Roger Miller · Post by **Roger Miller** » 15 Jun 2014 6:23 pm

I have a Blues Jr. and have issues. I have had all kinds of problems with this amp. My repair guy said that there is a resistor mismark on the schematic. It had something to do with oscillating signal. Gotta find a way to sell this and get out from under it, with out selling someone a worthless piece of equipment. You have nothing holding the preamp tubes in the sockets, so they are always loose and I've replaced the output transformer also. Fender is really cutting corners, I'm real upset with them.

Gary Meixner · Post by **Gary Meixner** » 16 Jun 2014 3:37 pm

Alvin,

I might look to the power tubes as the source of your troubles. As Jerry replied the bias is set very hot on these amp causing the power tubes to heat up a lot and fail prematurely. The excessive heat can cause the solder joints between the tube socket and circuit board to weaken and fail as well.

Working on these amps is quite easy: the hardest part is getting the circuit board out of the chassis. The circuit boards are surprisingly tough and once you have them out any repairs or mods are quite straight forward.

I would go to the Bill M site and read about his basic mod, adjustable bias mod and input jack mod. These are easy to do and solve most of the problems these amps have.

While you have the board out touch up the solder connects on the tube sockets, also read about how to re-tension the tube sockets - easy to do.

The instructions that come with the mod kits are very well done and easy to follow. I have done many of the mods he offers and they all have been very worthwhile but the basic ones I already mentioned will give you the most noticeable and immediate benefit.

Good luck,

Gary

Jerry Hedge · Post by **Jerry Hedge** » 16 Jun 2014 7:01 pm

You might try a a 12AY7 or a 5751 for the first preamp tube. They are both lower gain tubes, and you'll get more headroom and less distortion, and more usable volume.

Roger Miller · Post by **Roger Miller** » 20 Jun 2014 3:34 am

Gary, you repeated exactly what my amp guy said,except the mod. I might look into that mod. I have friends that have BillM mods, just not for sure I want to mess with it. I have one power tube socket showing heat distress, but it is working for now.

Gary Meixner · Post by **Gary Meixner** » 20 Jun 2014 11:04 am

Roger,

I just checked the Bill M site to make sure I gave you the right mods to consider. The Basic Kit for $22.00 is well worth doing and not that hard at all. The Re-Cap Kit for $10.00 makes a notable improvement as well. I wasn't going to bother with a re-cap at first, but then noticed the caps on my amp were leaking. Replacing the Jack for $10.00 just makes sense since the original is plastic.

You will need a decent soldering iron, solder, a meter, a solder sucker, some small diagonal cutters and a small drill - a Dremel works great.

I have poor near vision, but was able to do the whole job without to much trouble seeing. In the end, I was quite satisfied with the results. I got hooked on working on the amp and have since done just about every mod Bill M sells. They are easy and fun to do.

The amp has been banged around to practice and gigs for a couple of years now with out a bit of trouble, except for I did replaced the reverb tank.

If you are feed up with your amp I don't want to talk you in to anything, but if the amp already has a sound that you like, I think you will pleasantly surprised.

In the end, you will have a great sounding, loud and light weight rig.

Best of luck,

Gary

Kevin Raymer · Post by **Kevin Raymer** » 21 Jun 2014 3:36 am

I got one back in the day at a local music store for $150 because the reverb didn't work.
Have loved it ever since.

Mine is the American made version, and I wouldn't take $400 for it.

Alvin Douglas · Post by **Alvin Douglas** » 5 Jul 2014 2:50 pm

Thanks to those who responded and sorry for the time it took me to get back to this. I have done some reading about the BillM mods and think the right thing to do is order the parts and make the changes. I probably will wait until I get back to Florida (Nov.) to make the changes. However, I have always wanted a Fender Blues Deluxe so I bought one. A little heavier that the Blues Jr. but the sound is very nice. Have not had a chance to really get to know it yet but so far, I like the sound, especially the bass response. Again, thanks to everyone who provided advice. This site, the knowledge and willingness to share it is outstanding.
Alvin