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Post subject: Pro Junior Question
Posted: Thu Mar 19, 2009 11:44 pm
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Hi all,

So I recently became a member of the Fender amp club, as well as the tube amp club. I wound up getting a great deal on a Pro Jr. from a friend who is a professional musician. We played the thing together for hours and it worked just fine; after getting it home, it worked just great. However, after a lengthy (2 hr) jam at low volume with my band, I noticed something funny the next morning. I'll try to describe it as best I can...

At any volume over about 3 there occurs a strange tone whenever a note, usually on the bottom three strings, is played. It sounds a lot like a filament in a light bulb being rattled around. This instantly led me to believe that it was the tubes and, since the preamp tubes are brand-new Groove Tubes 12AX7s, I thought it might be the older power tubes (Sovteks, maybe?). After first tightening down everything that could be tightened on the cabinet and chassis and wedging a flatpick behind the metal nameplate on the back (easy fixes I didn't want to overlook) the rattle was unchanged.

My next step was to see if the spring clip holding the EL84s in was the problem. I removed it and the noise became even more noticeable on low and high notes -- chords, however, seemed to cover it until they decayed. Anyway, I put the spring clip back on and the rattle was diminished to its previous level. I'm more or less convinced that its the EL84s (though I could be wrong) dying -- the guy I bought it from did say they were old and would probably need replacing soon. Anyway, here is what I want to know:

1) Can I buy new GT El84s and stick them in without having to have a tech rebias the amplifier? I've heard that PJs are "self biasing," but I'm not exactly sure about all of this, being new to tubes and all.

2) What do you ladies and gents think of the spring clip? Keep it in or pull it out?

3) Finally, any other advice for a new PJ owner? By the way, I love the little box. It's a far cry from my old solid states -- even my Peavey Bandit 65, a good sounding SS amp, can't hold a candle to the PJ!!

Any and all advice or recommendations are appreciated!!! Thanks!


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Post subject:
Posted: Mon Mar 23, 2009 1:01 pm
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Yes - Just purchase a new set of tubes and install. That will probably take care of it. There is no such thing as a self biasing amp. The PJ is a non adjustable bias.....which means, just stick the tubes in. There is nothing you can adjust on the bias. A very very few guys will do a mod to install a bias pot to make adjustments, but forget that. The PJ's beauty is it's simplicty. Most 15 watt el84 amps are made this way.

Yes - Keep the springs on the tubes.


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Post subject: Pro Junior
Posted: Mon Mar 23, 2009 2:48 pm
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Okay, I got a new pair of Groove Tubes EL84s and two Tung-Sol 12ax7s. The amp immediately sounded better, if not quite so loud. Either way, it seems to have helped. That said, it looks to me like the first 12ax7 (on your right when facing the back of the amp) is ringing a bit. It must be the socket, because the tubes are brand-new and I've tried several. Can these be retensioned? Is that even possible, or could you jury-rig some sort of clamp to hold them down -- if I hold the offending tube with my hand, the rattle goes away. For the record though, it's WAY quieter with the new tubes, so that at least made a big improvement.


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Posted: Mon Mar 23, 2009 5:41 pm
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Vulkan,
I have the same problem as you - that same 'broken filament in a light bulb' sound. Sounds like the new tubes fixed your issue, so I will try the same. Thank you for posting your issue and following it up with an update. I'm sure I'm not the only one here that can benefit from this information.

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Post subject:
Posted: Mon Mar 23, 2009 10:55 pm
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Hey, no problem. Let me know how it goes for you as well. Also, I don't know if you know, but I've heard that Electro-Harmonix 12ax7s are some of the quietest on the market. I've also heard people say that they've tied down tubes with some form of creative solution. I've considered building a spring clip for them, same as is on the EL84s. That might be an easy fix.


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Posted: Tue Mar 24, 2009 5:58 am
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There is an old Pro jr. story that has been floating around for years pertaining to the sound you describe.

It is said that on the back panel there are screws that are too long and by backing them out a few turns the rattle/buzz goes away.

That being said (and I've found the story many times) My sons Pro jr. does not have the buzz and so I have never tried it.

Can't hurt to give it a try.

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Post subject: Long Screw
Posted: Tue Mar 24, 2009 7:42 am
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I've heard that story, actually. However, my PJ is relatively old; it's one of the made in America ones. Insofar as I know, the problem with the screw only plagues the MIM versions -- apparently the long screw comes into contact with the tone pot and creates a ground loop. I've tried removing it on mine with no discernible difference. MY PJ didn't have any sort of hum to begin with, only the "filament rattle" that I described earlier. New tubes seem to have remedied that too, which is great. Now I can get to work and make some loud music!


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Posted: Wed Mar 25, 2009 12:36 pm
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vulcan, Tubes can be finicky and that 12ax7 you mention, though new, still might be somewhat faulty. Try another one. It happens even with new tubes.

FWIW, I like the electo harmonix tubes too. I have a full set in one of my PJ's that I had JJ's in. I much prefer the EH's in the PJ.


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Posted: Wed Mar 25, 2009 2:28 pm
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Thanks Prolux. The Tung-Sols seem to work well, but I'll eventually get around to picking up some EH tubes and seeing what they can do for me!


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Posted: Thu Mar 26, 2009 4:51 am
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Check out Ruby tubes for the pre and GTs for the power. The GTs were oem for at least a few years in the late 90's early 2000's (might still be). I tried some hotter GTs in the pre and got a nasty squeal, but the Rubys are great. You really can't go too wrong with this amp. Mine is one that had the ground hum, so I removed one of the screws that holds the back panel on; the one between the Vol and Tone, and that took care of it. Still a little noisy when you crank it up, but I think a good amount of that comes from the Guitar and Cable anyway. Bottom line.... everyone should own one of these amps.

I have some Mulllards I'm thinking about tossing in if I get bored or actually need a retube. I'll let you guys know how they sound when and if I do.

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