Sub tube for 12ax7 (Fender Pro Junior Amp)?

[GNAPPI]

Hello my friends
any ideas how to reduce the amp's hum ?

Are you able to work on the amp without killing yourself? :-) If not take the amp to a tech and have him/her look at this link:

Used Pro Jr with inherited filter caps | The Gear Page

There are lots of "mods" for the PJ on the web. If yours is an earlier model with 22UF caps in all four psu filter locations, two of the HV PSU's (C15 C16) filter caps should upped to 47UF. If it's a III with one 47uf at C15 then a 100uf is your fix.

[lammie200]

well...after a long night,,,
i am not sure if i prefer 12au7 than 12ax7
maybe 5751 was a better idea

for sure there is dramatically less volume and hum, but there is a big difference in tone too
My 335 sounds thinner with the 12au7. Less bottom. Maybe 5751 it's better for projr,,,but there is a lot of money just to buy new tubes for test drive,,

Do you think that an old preamp tubes can cause hum ?
I am thinking to try a couple of new 12ax7 for my projunior because their about 6 years old now

I found that changing the output transformer to a Mercury Magnetics gave it more depth. BTW, I spent more than I should have to get my Pro Jr. right. It's the nature of the (jr.) beast I guess.

[KirkP]

well...after a long night,,,
i am not sure if i prefer 12au7 than 12ax7
maybe 5751 was a better idea

for sure there is dramatically less volume and hum, but there is a big difference in tone too
My 335 sounds thinner with the 12au7. Less bottom. Maybe 5751 it's better for projr,,,but there is a lot of money just to buy new tubes for test drive,,

Do you think that an old preamp tubes can cause hum ?
I am thinking to try a couple of new 12ax7 for my projunior because their about 6 years old now

I've read that the 12AU7 could harm your plate resistor due due high plate current. It's too dissimilar to a 12AX7 to expect good results without modifying the circuit.

Some vendors encourage substitutions, but they have a financial incentive to do that since it drives up sales.

Tube substitution make the most sense for folks who want to drive them into clipping and are looking for different breakup characteristics. Since I play clean, I'm more concerned with having a good quality tube that my preamp circuit was designed for. I've substituted tubes a few times, but got much better results from experimenting with tone and volume control settings, both on the amp and guitar.

[KirkP]

This guy is talking about the Blues Junior not Pro Junior, but his advice seems very good...
http://billmaudio.com/wp/?page_id=131

[jkstigma]

great article

have you ever read this one ?
http://www.instructables.com/id/Mod-...o-Jr/?ALLSTEPS

take a look at step 8 and 12

[Endorphins]

experiment

[jkstigma]

before 5 years i replaced the stock factory tubes with jj tubes

yesterday i found the old factory tubes....a don't know which company made this tubes for fender....but on the tubes it's writing just... <Fender 12ax7a>

..i just took the one of them and put it on V1 !!!

Much less bzzzzzzzzzzzz () and wonderfull sound

12ax7a ???

in groove tubes i can see only 12ax7 C or M or L

i just read on the net that 12ax7a has a spiral filament to reduce hum that is the difference, is that truth ?