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Post subject: Pro Juinior III
Posted: Fri Sep 26, 2014 8:58 pm
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Hi I'd like to ask some questions regarding my Pro Junior III

Is it normal
1. ...to still hear sound/output even if my volume is at zero?
2. ...to hear some popping sound during the first minute upon turning it on?
3. ...to hear a squeal during the first minute upon turning it on?

I have not changed any of the stock (Groove) tubes nor have I dropped it in any way.

Thanks!


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Post subject: Re: Pro Juinior III
Posted: Fri Sep 26, 2014 9:14 pm
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Hi vantonilin,

Many amps will have some sound out when the volume is at zero, no big deal, just turn down the guitar volume.

As to the popping and squealing, you might have a bad tube, likely V1, the first tube on the right looking at the back of the amp. V1 is the first preamp tube, the next small tube is the phase inverter (PI), followed by the two larger output tubes. The noises could be from any of the tubes, and substitution is a good way to check.

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Post subject: Re: Pro Juinior III
Posted: Fri Sep 26, 2014 9:38 pm
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Thanks for the reply! :D

I thought of swapping them thinking that both are 12AX7s, but upon looking at the manual, each has a different part number. Also on the tube itself they differ in one label. V1 is marked "1108" while the second is marked with "1107". Okay, I'll try swapping the pre-amp tubes. Should I still do this for the power tubes? Thanks again!


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Post subject: Re: Pro Juinior III
Posted: Fri Sep 26, 2014 9:51 pm
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V1 is marked "1108" while the second is marked with "1107"

Just date codes.

The different part numbers are probably just different brands, but if they are the stock tubes, both are 12AX7, so it's OK to swap. Swapping might change the noise and give you an indication if one is bad, but it's better to substitute a known good 12AX7 into each spot one at a time. Try the new tube in V1, if no difference, replace the original and try the new tube in the next spot. Swapping the output tubes positions won't make any difference.

Oh, note the gap in the tubes' pins and be sure to align with the socket.

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Post subject: Re: Pro Juinior III
Posted: Sat Sep 27, 2014 8:24 am
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FYI...A "Known Good Tube" does not necessarily mean a new tube, but one that has performed correctly.
:wink:
T2

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Post subject: Re: Pro Juinior III
Posted: Sat Sep 27, 2014 8:53 am
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Excellent clarification T2. 8)

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Post subject: Re: Pro Juinior III
Posted: Sat Sep 27, 2014 3:36 pm
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I swapped both 12AX7s and the squeal changes. The squeal was short and could be heard a minute after turning the amp on. Now (after the swapping) the squeal came a few seconds after turning on the amp. Noticeably, it was longer and had a hum.

Would this give a clue to which 12AX7 is busted?


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Post subject: Re: Pro Juinior III
Posted: Sat Sep 27, 2014 6:47 pm
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I'll stick with my initial guess, likely the tube that was in V1 is the culprit.

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Post subject: Re: Pro Juinior III
Posted: Sat Sep 27, 2014 6:57 pm
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Thanks shimmilou!


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Post subject: Re: Pro Juinior III
Posted: Mon Oct 27, 2014 7:32 pm
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Hello again, sorry to get back on this topic so late.

I am now considering purchasing new 12AX7 tubes. As 12AX7 tubes are hard to come by here, would there be issues if I replace it with a tube from another brand? I mean, I've seen so many kinds of 12AX7s out there, I'm not if they will be good replacements.

Thanks in advance!


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Post subject: Re: Pro Juinior III
Posted: Mon Oct 27, 2014 8:48 pm
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Any 12AX7 will be interchangeable with any other 12AX7. Some will be better than others, but they will be interchangablee. Other tubes that be used are lower gain tubes like a 5751 or 12AY7, which can result in cleaner sound.

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Post subject: Re: Pro Juinior III
Posted: Mon Oct 27, 2014 11:46 pm
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also ecc83=12ax7 same tube different designation. ecc803 also a possibility.


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Post subject: Re: Pro Juinior III
Posted: Fri Oct 31, 2014 4:30 am
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I was able to replace the V1 tube with a new one (JJ), with hopes that they are working ones. Not sure how to make sure they work.

Anyway, no improvements. :( Squeal was still there. I tried to put the new one on V2 and it made the same squeal as placing the old GT V1 on V2 position.

Should I have bought a pair of JJs? instead of just replacing V1?

Hmmm dunno where to go from here. If there is some more checks I need to do, please let me know.

Thanks!


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Post subject: Re: Pro Juinior III
Posted: Wed Nov 19, 2014 6:56 am
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Purchased a new pair of TADs. 1 12ax7WA for V1 and 12ax7A-C on P1. Seems the squeal has gone, but I've noticed hum from the amp and the zero volume I've initially posted has become loader - at zero volume it seems the volume is set at 20% of the Max. All from replacing the pair of Groove tubes? hmmmm seems strange... :)

Hope you guys could share your thoughts. Thanks!


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Post subject: Re: Pro Juinior III
Posted: Sat Jan 13, 2018 7:47 am
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While I realize this thread was created and discussed in 2014; it would have been nice to know if he was experiencing the "popping & squealing" with just the amp---or was an instrument cable plugged into the amp.

A plugged in instrument cable can cause noises all it's own if the instrument end of the cable is unplugged and laying on the floor (grounded), or plugged in with the guitar volume up (on high gain), or even if the chord itself or input jack of the guitar are junk.

Could have been an issue that didn't even involve the tubes---but I reckon we'll never get to know the outcome in this particular case seeing as how the OP has been gone for 3 years and 2 months.

With a quality instrument cable, plugged into a quality guitar, I have absolutely no unsolicited noise (other than the common low tube hiss these amps are known for) coming from my Pro Junior III with any of the knobs set at any levels. i.e.: I can turn the amp AND guitar volumes all the way up, and if I don't touch the guitar strings as it sits in the stand, it makes no noise at all.


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