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Post subject: Blues Junior Volume Drop
Posted: Thu Jun 24, 2010 6:36 am
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Hi all, tonight I used my Blues Junior at Band Practise and was happy with it's tone and ability to keep up with our drummer.

However during a couple of songs into our second set...I noticed that the BJ was dropping in volume.

I have never experienced this with any amp before.

I turned the amp off, we had a 10 minute break..when I turned the amp back on...whammo the volume levels were back to normal.

Can anyone please put some light on the subject as to whether I am experiencing tubes failing as a result of overheating?

about 6 months ago I aksed an amp tech out of curiousity what mods does he normally do to BJ's.

His words were

"Well if you want it to be a giggin amp, put a set of JJ's in it and an internal cooling fan to keep the valves from running to hot and dropping out".


Do you think this is the case?

Appreciate any experienced advice...

Cheers.


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Posted: Thu Jun 24, 2010 3:13 pm
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wow i had figured someone at this point would have had an answer for you.
just do what the amp tech said to do.
did you call fender on this problem?


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Posted: Thu Jun 24, 2010 3:15 pm
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It's quite possible that some of your valves have come partially unseated -- this can occur because of regular use as much as abuse. Just firmly push them into their sockets. After making sure they're cold, of course.


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Posted: Thu Jun 24, 2010 3:19 pm
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I'm a long time user of the BJ and I've never had that happen in 10 years of gigging mine and have never fitted a cooling fan.

Did you have the JJ tubes fitted? if so, was the amp's bias checked? Cooling the bias off will prevent it from overheating, a decent amp tech can check it and change a couple of resisters to get the bias cooled/corrected.

Incorrect bias setting will cause it to run too hot especially after replacing the stock Sovtek tubes with JJ's, and it's better to have a decent amp tech address that as the root cause rather than fit a fan which is not addressing the hot bias causing the heat.

Get it checked sooner rather than later as with the hot bias over-heating the pcb and then cooling off as you switch off the amp, over time, will expand and contract the solder joints on the pcb where the tubes plug in more than usual, this is already a problem area on the BJ and will be made worse if it's getting cooked.


Cheers,

Snowy


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Posted: Thu Jun 24, 2010 3:58 pm
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Hi Vulkan, Mate I checked the valves during the rehearsal and they were seated correctly. I know what sound to listen for when they start dropping out because this has already happened to me at home.
Thanks for the advice though.

G'day Snowy, yeah I will be taking the BJ to an amp tech today to first check the biasing, secondly consider putting JJ tubes in it that will give me more clean headroom.

I will hold off on the cooling fan for now. My fear is that if I am playing a gig and all of a sudden I have a melt down of the tubes and pcb.

I will discuss all options with the tech.

Apparently he is the best amp tech in Adelaide.

Cheers Guy's...I will get back to you by the end of the day.
8)


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Posted: Thu Jun 24, 2010 4:04 pm
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Good luck with it mate.

The JJ's are good tubes for the BJ you can't go wrong there, as you said just get the bias checked especially with the new tubes to get the best life out of them and the amp, it's usually too hot on the BJ even out of the box with the factory Sovteks fitted.


Cheers,

Snowy


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Posted: Fri Jun 25, 2010 12:09 am
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No457 Snowy wrote:
Good luck with it mate.

The JJ's are good tubes for the BJ you can't go wrong there, as you said just get the bias checked especially with the new tubes to get the best life out of them and the amp, it's usually too hot on the BJ even out of the box with the factory Sovteks fitted.


Cheers,

Snowy


G'day Snowy and all...

Well here is the end result.

I spoke with the amp tech today.

Once again stated to me that he would swap out the GT's with either JJ's or other tubes and also install a cooling fan.

resulting costs anywhere up to $300 au. I won't be spending that amount.

I rang around to some stores to hear varying opinions to that of

"Just keep on top of your tubes, "Tubes are like spark plugs in a car"

I like that saying, I never heard that before... :lol:

Anyway I ended up replacing my two old GT power tubes with two
Electro Harmonic EL84 EH tubes.

Well now it seems that my Blues Junior came to life again. I now have better BASS/MID/TREBLE responses than before and the volume dials up quicker.

I think the GT's just saw out their time.

I will see if I experience any volume drop at out next rehearsal.

ohhh here is a kicker.

The amp tech stated that Blues Juniors do not need biasing? On that basis that is why I have gone out and replaced the tubes myself.

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Post subject:
Posted: Fri Jun 25, 2010 12:33 am
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No disrespect to your amp tech but I think I would trust Billm's word on the bias, he's world renowned as an authority on the BJ and has worked on more BJ circuits than probably anybody on the planet. (he has personally modified over 1000 Bj's)

From his website, 4th paragraph down:

http://home.comcast.net/~machrone/bluesjunior.htm#Bias

I'm not sure why your tech would say the bias doesn't need checking (and possibly needing to be adjusted by a resister change) when changing tubes. Your amp will probably be just fine but it will probably run hot and almost certainly your new tubes will die faster.

Cheers,

Snowy


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Post subject:
Posted: Fri Jun 25, 2010 2:09 am
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Yeah well that's what I thought.

I have always been under the impression that any tube amp has to be biased in some way.

Maybe I misunderstood him but I will see how things go with the new tubes.

I have never taken my amp to a tech in my life.

I can see it happening one day though..

Has anyone out there used Electro Harmonic EL84 EH tubes? If so what do you think of them.


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Posted: Fri Jun 25, 2010 6:08 am
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No457 Snowy wrote:
No disrespect to your amp tech but I think I would trust Billm's word on the bias, he's world renowned as an authority on the BJ and has worked on more BJ circuits than probably anybody on the planet. (he has personally modified over 1000 Bj's)

From his website, 4th paragraph down:

http://home.comcast.net/~machrone/bluesjunior.htm#Bias

I'm not sure why your tech would say the bias doesn't need checking (and possibly needing to be adjusted by a resister change) when changing tubes. Your amp will probably be just fine but it will probably run hot and almost certainly your new tubes will die faster.

Cheers,

Snowy


No disrespect to you or Bill, he Sells mod kits and mods amps. It's nice he shows you what an oscilloscope reads with hot and cold biased tubes, but last time I looked an oscilloscope didn't have ears. He tells you the tubes are cooking and you his mod can help adjust it. Right away the new guy thinks, "Oh my God, mu tubes ore cooking and they might melt!" The amp was biased that way for a reason and a good EL84 will take the heat. If they're not red plating it's not too much of a problem except you won't get a lot of headroom and the tube life will be a little shorter. You should always have a spare set of tubes anyway. I would have the bias checked, I'd leave the fan out. You can just get a small desk fan and point it towards the back of the amp for air flow. The great thing about the HRD series amps are they created little cottage industries for mod's, mod kits and repairs from modding the amps yourself. I you need to mod it, just change the tubes and speaker. You'll make a much better improvement the amp.

As far as modding an amp goes, it will void your warranty period. I don't see Bill picking up the rest of your warranty using his mod kits. Just go to www.eurotubes.com or pick up some JJ's locally if you can and you should be fine. Have the bias checked or pick up a bias probe or a multi meter. Your amp will not spontaneously combust. EH tubes aren't bad at all. I prefer JJ's, but we all have different ears and different tastes. Go to Eurotubes site and check out the biasing information. There are videos too. $300 for a tube change, bias check and a fan? I'd look for a new tech just because of that. :wink:

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Post subject:
Posted: Fri Jun 25, 2010 7:42 am
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63supro wrote:
No disrespect to you or Bill, he Sells mod kits and mods amps. It's nice he shows you what an oscilloscope reads with hot and cold biased tubes, but last time I looked an oscilloscope didn't have ears.


So is your method to check distortion when you bias is to listen to the speaker?

The tech probably said it doesn't need biasing because it has a fixed bias.


Last edited by Shockwarrior on Fri Jun 25, 2010 8:12 am, edited 1 time in total.

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Post subject:
Posted: Fri Jun 25, 2010 8:11 am
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It's part of the process. I listen, then check the bias voltage. If it breaks up too early for my taste, I drop the voltage slightly until l I get it to where I want it. I usually get 2-3 years out of new production tubes. I got 25 years from my 76 Twin and the RCA 6V6 in my 74 Champ just started to rattle after 36 years. Still sounded great tone wise but the mechanical rattle drove me crazy.

An oscilloscope is great for what it does, but like I said, it doesn't have ears and it doesn't have musical taste either. You can trust your ears or trust sine waves, it's up to you. There's no right or wrong. My ears work for me. You can be technical and that's fine but to say tubes biased warm or hot doesn't sound different than a tube biased cold because the scope says so is just ridiculous. Tubes biased cold (over biased) last longer but sound lifeless and sterile to my ears. My JJ's in my HRDlx were biased between 82-85Mv and sounded great. If you biased GT's like that they cook and fail.

IMO, A quality tube will be okay, a substandard tube will fail early regardless of how it's biased.

Bill doesn't play my rig, I do. Just because someone has a opinion doesn't mean I have to bow down to it. A lot of younger players read this stuff and automatically think their amp sound rotten and they have to mod their amps even though they may have been happy with it before they read all that stuff. Trust your own ears. Fargen mods amps too. They tell you all your components are substandard and how wonderful the mods will make your amp sound. Personally I wouldn't sink that kind of money into any amp. I'd build one first. Just my opinion, flame away if it makes anyone happy.

All this is why I try to steer folks away from the HRD series amps.

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Post subject:
Posted: Fri Jun 25, 2010 3:09 pm
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No disrespect taken Supro, I suggested he get the bias checked, and I'll stand by that advice.

Cheers,

Snowy


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Post subject:
Posted: Fri Jun 25, 2010 3:14 pm
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hey guys, please go give some advice on my blues jr question in the
lounge please.


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Post subject: Tube biasing
Posted: Tue Jun 29, 2010 8:26 pm
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Over or under-biasing tubes will change the sound of the amp, but it is not the best option for changing the sound and can adversely affect the life of the tube or other components associated with the tube. If a manufacturer has specs for their product, it is usually advisable to follow those specs for best performance and longest life. Tube manufacturers know what they are talking about, so do good techs, like Billm. I have a degree in electronics and have about 25 years experience with electronic equipment of all types, including tube amps, and it seems from my experience that any equipment which is properly set up performs better and lasts longer than equipment that is not.

I think that you will find many new Fender amps come from the factory with improperly biased tubes (Blues Junior anyone?). I think that many complaints about sound can be remedied with with a proper setup. Tubes are meant to be over driven to provide a good sound, but not by cooking them with unnecessary extra heat. The bias specs can vary a lot from tube to tube, even the same type of tube from two different manufacturers, so it is important to set your bias correctly for each tube.

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Last edited by shimmilou on Wed Jun 30, 2010 3:50 pm, edited 1 time in total.

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