Blues Jr. Upgrade secrets

[Tiny_Daddy]

Blues Jr. came in, oscillating. Reason was, the three 22uF capacitors were all leaking their guts out. Replaced those. Also replaced the output transformer with the larger Hammond 1750H (built for Deluxe w/ 6V6) and added a Presence pot: 100K, audio taper with 56K resistor in series with the low-resistance side. This gave a fairly smooth control and stock feedback at midpoint. Now it plays like a big amp!

[Fresh_Start]

Interesting about the leaky caps.  How old was the amp?

You're probably way ahead of me, but I added adjustable bias and have photos somewhere if you're interested.  IMHO my approach was as good as the Blues Jr. guru's but YMMV.

Cheers,

Chip

[LooseChange]

Fender messed up a run of these... The caps were bad. I've repaired two with the same problem.
OT upgrade does wonders for this amp.

[Fresh_Start]

Fender messed up a run of these... The caps were bad. I've repaired two with the same problem.
OT upgrade does wonders for this amp.

Did you use a Mercury Magnetics OT?  I bought one but haven't installed it.  Wanted to bias using the OT resistance method and one side of the OT primary had much lower resistance than the other.  MM assured me it was normal, but we're talking 75 ohms vs. 100 ohms.  Stock OT was exactly the same on both sides.

Cheers,

Chip

[LooseChange]

Yes, Mercury. Never measured it.  Every amp I modded sounded MUCH better than stock.  I like adding another 20uf to the first filter cap too.  With the added response from the OT you get better bottom end and you will hear a bit more hum. That filter cap addition does the trick.

[Fresh_Start]

Good tip on the filter cap.  I've often thought that a choke between the plates & screens would be an improvement too.

Unfortunately, my 2001 "green board" Blues Jr. has too many Mexican/PCB gremlins in it.  I did lift the board out to put in the adjustable bias but was very careful.  Even so, I've had problems on and off with the tube sockets having poor contact.  The input jack is shot.  I've re-soldered the tube socket connections too.  It will work OK for a while, and then some new noise or problem comes up.  Did I mention that I hate ribbon cables?

At this point, I'm going to gut the amp and build one of the tubenit/Geezer & Co. designs in it instead of trying to make the damned thing work well.

Cheers,

Chip

[Tiny_Daddy]

I have re-built Blues Jr. using a generic turret board, but had to make a PCB to hold the reverb, channel switching, etc.

[bigdaddy]

I think we'll all agree that there are some basic changes/mods to make to production amps that will improve them immensely. Had they done it at the factory the amp would have been twice the cost. But it's basic stuff you learn by doing it. Good quality parts makes a difference in sound quality and reliability.