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

[jkstigma]

Hello my friends

i have a fender projunior made in usa 15w,
I am playing with this amp at home
the preamp tubes are 12ax7

is there any sub tube i can use for better jazz tone,,,,in bedroom volumes ?
any ideas how to reduce the amp's hum ?

[mongrel]

I've got a Bugera V22 that has the same tube compliment. It came with the stock Bugera tubes in the three pre-amp positions but the EL 84's had been swapped for JJ's. I had some 12A family tubes in my drawer so I experimented a bit. In the phase inverter position, V3, I swapped the 12AX7 for a 12AT7. I tried other brands of 12AX7's in V1 and V2 including EH, Fender (7025) and Ruby with varying results but the biggest change came with putting a 12AU7 in V1. This is a very low gain tube that seemed to drastically reduce volume but cleaned the amp up to a great clean and warm jazzy sound perfect for bedroom level playing. I think that the best compromise tube might be a 12AY7 but I haven't gotten one of those yet.

[D.G.]

5751 for v1 and 12au7 for v2

[SamBooka]

Ah the hum.. rings a bell. I havent plugged mine in for years. Bear with me.. I am old..

I am used to fender amps .. still have a few. Got my BJ and was like WTF.. noisy.. nasty.. thank god I got a good deal on it.

Noisy.. was really just a matter of getting the master and main volumes right.. my first reaction was crank the master and use the pre volume like any other fender. Bad idea.. keep your master around 8-9 out of 12 and then use your pre.

If you use reverb it sounds nasty.. a replacement belltone or MOD tank from Antique Electronics is less than 20$ and well worth it and easy to do.

5751.. sure.. why not Not a fan of the 12au7 .. some people like 12at7s but dont like those either.. 12ay7 can be interesting in V1 on some amps but I have a funny feeling a decent 12ax7 in there is always the best bet.

[wildschwein]

You can use 12AT7s, but as they're more of a driver tube they're not actually the best sub for a 12AX7. 5751s will tone things down a little. 12AY7s were often used in vintage Fender front ends and will clean up things nicely.

[LyleGorch]

5751

[Greentone]

The Pro Junior is maybe the most under-rated Fender amp of all time. It is, IMO, the best amp in their 90s reissue/vintage-y series of amps, until you work your way up to the '59 Bassman RI. Lots of people have bought the Blues Junior--Fender sold gobs of them, and I own two, myself. There is simply NO comparison. My Pro Jr blew the two Blues Juniors away. Part of it is that the 10" speaker is better is better sounding than the 12" speaker (my PJ came with the blue-frame Eminence alnico speaker...the amp was one of the first-year series). Another part of the equation is that the volume control of the Pro is magic--turn up and things just get better and better.

I think that the best V1 tube for a clean sound is the 12AY7. I use NOS RCA, but I got decent results from the Electro Harmonix new issue tube, too. For V2 I have experimented but keep coming back to a Mullard 12AX7, FWIW.

Cheers.

[SamBooka]

Sorry all, I am a freaking idiot.
like I say, I'm getting old. I was referring to the blues Junior. You're talking about the Pro Junior.
my comments about the reverb tank you can disregard.

my tube comments stand but what I found with my Pro Junior is that it is a raw little amp that likes to be cranked.
I really wouldn't go any lower than a 5751. It doesn't have the typical fender scoop mids that you see on blackface and silver face amps. If you like a little bit of a hair on your tone try this thing with P90 and get your grant green on!

PS. I am still old when I'm writing this but I also haven't had my coffee!

[bananafist]

5751, 12AY or 12AT7. Needn't be NOS. See which you like best. Not too familiar with the Pro Jnr, but in my other Fenders, a 12AU7 as phase inverter, adds cleans, if ya know what I mean.

[Greentone]

Sambooka is correct about the Pro Jr's shading of the tone palette towards mids--no blackface "scoop." It is the "tweedy-est" of the '90s amps, other than the '59 Bassman RI.

[D.G.]

5751, 12AY or 12AT7. Needn't be NOS. See which you like best. Not too familiar with the Pro Jnr, but in my other Fenders, a 12AU7 as phase inverter, adds cleans, if ya know what I mean.

This is what I have in my Pro Jr: 5751 in the preamp slot and a 12AU7 in the phase inverter. What it does in my amp is remove most of the idling hiss so it's only a tiny bit hissier than my PRRI. It also cleans the amp up significantly to the point that when dimed my Strat just gets a nice breakup, but not the full-on melt-down that a pair of 12AX7's give it.

I HIGHLY recommend trying it out!

[snoskier63]

Greentone, or anyone else that may know...

In looking for a 12AY7 tube for my Pro Junior amp some descriptions mention a 2-3% section balance and some do not. What exactly does that mean?

Also, each tube lists a "Gm" value. What is that, and is there a more desirable value for clean tones through a Pro Junior?

Thanks!

[Greentone]

Here's a refresher on how vacuum tubes work. As Thomas Edison discovered, a filament (hot wire) in a evacuated glass bulb will cause electrons to be emitted. They will hit the glass and darken the bulb (as they did in the earliest lamps). Inserting a positively charged plate into the bulb (an anode) creates a DIODE. Electrons will be emitted from the heated filament (in this case serving as a directly heated cathode) and gather on the surface of the anode. The diode permits the flow of current in one direction only. (GZ-34, 5Y3, and 5U4 rectifier tubes are dual-diode tubes, i.e., they have two diodes in a single glass tube.) Lee DeForrest is credited with inserting a third element into the tube, the grid, between the cathode and the anode. Applying a small, negative voltage to the grid, DeForrest discovered that he was able to _amplify_ the signal impressed at the grid of the tube. Edison invents the vacuum tube (the lamp), Fleming invents the diode, DeForrest invents the triode. Ta-da, radio and amplification is born.

The 12AY7 and 12AX7 tubes are part of the family of dual-triode tubes that came along in the early 1950s. They represent high-amplification tubes with the capability of amplifying a low-power signal by a factor of 60-1 and 100-1, respectively, by running the signal in series through the two triodes in the tube.

The ratings you see indicated for the tube refer to how balanced the two halves of the twin triode are with each other. The numbers refer to the transconductance of the triodes. Transconductance is the ratio of (the change in the plate, ie, anode, to cathode current) divided by (the change in the grid to cathode voltage). In other words, how does changing the voltage from the grid to cathode change the flow of current through the tube. Transconductance is the reciprocal of transresistance. Resistance is measured in ohms. We used to measure transconductance in "mhos" (ohms backwards). For the last hundred, or so, years we have used the Siemens international unit, or Si. You see transconductance (in gm) listed on the tube box. For most purposes you would like the two halves of the tube to be within about 20 percent of each other.

Me? I just listen to the tube and decide if I like it. Keep it simple.

[kraml]

This will sound techno-geeky, but you want a GE, black-plate, triple-mica, JG-5751-WA. These have a better sound than any of the others, especially the later (80s) grey plates. Put it in V1 as others have said. If you like clean, you will love it. k

P.S. An RCA or Beckman (same) 12AT7 black plate as a phase inverter will also smooth it out some (more).
P.P.S. Sorry to keep editing, but just realized that you have a low gain amp. The 5751 swap makes a lot more audible difference in high-gainers.

[snoskier63]

This will sound techno-geeky, but you want a GE, black-plate, triple-mica, JG-5751-WA. These have a better sound than any of the others, especially the later (80s) grey plates. Put it in V1 as others have said. If you like clean, you will love it. k

P.S. An RCA or Beckman (same) 12AT7 black plate as a phase inverter will also smooth it out some (more).
P.P.S. Sorry to keep editing, but just realized that you have a low gain amp. The 5751 swap makes a lot more audible difference in high-gainers.

I wound up ordering the following:

12AY7 GE NOS rebranded RCA "U" getter halo around 1960

[Greentone]

snoskier 63

Good choice. You will like those a lot. I have a sleeve of them, myself. Good tubes.

[snoskier63]

I just installed the 12AY7 in v1 this morning, and what a difference! Very warm with much smoother highs, and much improved clean headroom. I can't get the volume cranked in my house because it's just too loud, but I turned the volume to 6 (12:00) and there was not a hint of breakup. With the original12AX7 the speaker started to break up at around 10:30 - 11:00.

Also, today I demo'd my neighbors Joyo American pedal through my Henriksen JazzAmp 112. I was very surprised and impressed that the tone and dynamics I was able to achieve was very similar to my newly modded Pro Junior tube amp. I will have to get me one of these pedals!

[Greentone]

Well done. The 12ay7 is a good tube.

[jkstigma]

i just installed a 12au7 in V1 !
Goodbye 70% of hum

There is a big difference in volume,
12au7 has less volume than 12ax7

I can hear a difference in tone too... but i am not sure...yet

[339 in june]

Not a Fender,but a Fryette Memphis 30, I had good results with 12AY7 in V1. In fact, I got sort of two clean channels, less volume, nice but different tone, maybe a loss in dynamics (no problem with hum in any case with this amp)
I finally switched back to 12AX7 and prefer roll down guitar volume, but maybe some day ...I'll swap it again

[TedBPhx]

In the Peavey Classic 30 I use a 12AX7 for rock or blues and pop in a 5751 for clean jazz. Both are JJs and relatively inexpensive.

[GNAPPI]

I made a pre-amp with two 12ax7's and never was able to "warm" up to it and it got real dirty too fast. I put a 12AU7 up front as the input tube and it came alive.

Don't be afraid to diddle with lower gain tubes. Here's a chart of the subs with gain shown relative to a 12ax7.

[KirkP]

A couple of people mentioned balancing tubes. There are only two cases where you might want balanced tubes:
1) they are in a push pull configuration (e.g., a phase splitter or output stage)
2) you have a stereo amp and need to balance right and left channels.
I don't know of a reason to balance preamp tubes in a guitar amp.
(Other than that clarification greentone's overview is great.)

[lammie200]

I did the 12AU7 & 5751 combo in mine. Took care of a lot of the hum. I also changed the output transformer to a Mercury Magnetics. That added a lot of depth. It also came with a Jensen ceramic speaker which is similar to the stock but probably woke it up a bit. I wanted to go the extra mile so I sent it away to be recapped and re-resistored. They also messed with the bias to keep the tube life in my favor. The remaining hum is now mostly gone. It is pretty quiet but full sounding when played.

Just recently sold my Seymour Duncan convertible 100 watt combo. (I have quite a few pre amp modules if anyone is interested. They will eventually go on Ebay for cheap.) I took the Duncan money and bought a Fender Super Champ X2. Unlike the Pro Junior, an alnico speaker will fit easily so that is my next step. It is very quiet though. No electronic monkeying on that one.

[jkstigma]

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