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Post subject: Re: Blues Jr iii consistently blowing power tubes.
Posted: Wed May 25, 2011 1:44 pm
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Rossfloss,

Any new tube required a bias check, If you don't do that you take chance. If the tube don't blow it doesn' mean the bias is ok. the rigght bias save tubes AND give the best tone.

Nobody who know electronic and bias will tell you another thing. To bad it's trouble to learn how to bias or to find a good tech and it cost $$$; no choice util you want to play lottery and have a poor sound.

In the case of Blues junior; you must find a good tech because he have to replace some resistors to adjust bias.


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Post subject: Re: Blues Jr iii consistently blowing power tubes.
Posted: Wed May 25, 2011 1:52 pm
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+1 stratele52 :)

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Post subject: Re: Blues Jr iii consistently blowing power tubes.
Posted: Wed May 25, 2011 2:35 pm
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+10 Stratele and Shimmilou 8)

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Post subject: Re: Blues Jr iii consistently blowing power tubes.
Posted: Tue Jun 07, 2011 8:03 pm
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I have blown the power tubes a couple of times by having a sabotoochie pedal hooked to the amp.


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Post subject: Re: Blues Jr iii consistently blowing power tubes.
Posted: Tue Jun 07, 2011 8:05 pm
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He probably changed the C- voltage from the factory setting of about -10V to about -14V, which sounds very close to the setting on mine. That has to translate to much cooler idle for the stock output tubes, although without checking the current draw of the tube, we won't know the actual idle wattage. Did your tech happen to mention anything about tube current measurements, or wattage? Those are the important numbers to know, the C- voltage is irrelevant in knowing the actual tube current draw, even though raising that voltage (more negative voltage) is generally beneficial in this case.

At any rate, your output tubes should last much longer now. :)

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Post subject: Re: Blues Jr iii consistently blowing power tubes.
Posted: Wed Jun 08, 2011 2:07 am
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If tubes are biased too hot, a high input signal, like a pedal, can make tube working too hard and destroy.


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Post subject: Re: Blues Jr iii consistently blowing power tubes.
Posted: Wed Jun 08, 2011 11:18 am
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I understand that it's a good idea to bias. But i don't have a good tech anywhere in the area so unfortunately taking a chance is what I'll have to do.

So back to my question, if I put in power tubes that have a cleaner rating of 10 wouldn't they not get as hot as the tubes rated at 7, holding all else (including bias) constant?


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Post subject: Re: Blues Jr iii consistently blowing power tubes.
Posted: Wed Jun 08, 2011 11:43 am
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Sorry Ross, but there's really no way around a bias check in a fixed bias amp. Look around on youtube, I'm sure there's a biasing video for your amp somewhere.

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Post subject: Re: Blues Jr iii consistently blowing power tubes.
Posted: Wed Jun 08, 2011 12:20 pm
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Rossfloss,

I agree, checking is the only way to know exactly where you are with the current draw of any particular tube. With GTs, and some other brands, if you replace the tube with the exact same tube including rating number, you are likely to have the same current draw. Any change in the new tubes specs and the current draw will likely be different with the same bias setting in the amp.

You mentioned taking a chance, which is what many BJr owners do, by just trying the new tubes to see what happens. Your best bet in that case, is to install the new tubes, and watch them closely as you play in a dark room to see if the Plates start to glow red. If the Plates start to glow red then you have a problem, turn off the amp immediately and put the stock tubes back in. If after several hours of play the Plates are not glowing red, you may be alright, although I would keep my eyes/ears on them for a lot longer period of time. Don't confuse the orange glow of the filaments (heaters behind the Plates) with the red glow of the Plates.

This would be a great opportunity to check the temperature of the stock tubes at idle, and compare to the temperature of the new tubes. The temperature at which the tubes idle will be a good indication of whether or not the new ones run hotter. :idea:

I would think that simply installing some new GTs in your amp would surely not void the warranty. :D

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Post subject: Re: Blues Jr iii consistently blowing power tubes.
Posted: Thu Jun 09, 2011 11:44 am
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shimmilou wrote:
Rossfloss,

I agree, checking is the only way to know exactly where you are with the current draw of any particular tube. With GTs, and some other brands, if you replace the tube with the exact same tube including rating number, you are likely to have the same current draw. Any change in the new tubes specs and the current draw will likely be different with the same bias setting in the amp.

You mentioned taking a chance, which is what many BJr owners do, by just trying the new tubes to see what happens. Your best bet in that case, is to install the new tubes, and watch them closely as you play in a dark room to see if the Plates start to glow red. If the Plates start to glow red then you have a problem, turn off the amp immediately and put the stock tubes back in. If after several hours of play the Plates are not glowing red, you may be alright, although I would keep my eyes/ears on them for a lot longer period of time. Don't confuse the orange glow of the filaments (heaters behind the Plates) with the red glow of the Plates.

This would be a great opportunity to check the temperature of the stock tubes at idle, and compare to the temperature of the new tubes. The temperature at which the tubes idle will be a good indication of whether or not the new ones run hotter. :idea:

I would think that simply installing some new GTs in your amp would surely not void the warranty. :D



Thanks! And thank you Supro as well. I guess the reason I was so adamant about that question is because the GT EL84-R's that came stock seem to run fine. I've used them everyday since I've gotten the amp and I've never noticed the back of the amp getting too hot. Maybe the bias is actually somewhat in the appropriate range? I was just wondering if cleaner tubes would for sure not draw as much current which would therefore, like the tubes I have now, not overheat. But as you said there is no way of telling, so I might just do it the broke way and try by observation like you suggested Shimilou. Iif this doesn't work I'm going to need to plan a weekend trip to Lawrence or Kansas City.

Off topic:
BTW Shimilou, I've never been the biggest fan of this used hotrod Deville 410 I got. It always seemed to be way to bassy and not have enough highs. I know your a big time fan and user of the Deville so I figured mine was just lacking. I started messing with different preamp tubes and learned it was just the stock Fender tubes causing all those tonal characteristics I wasn't liking (I can't believe how big of a difference tubes make on some amps).
Anyhow, after a couple hours of extensive tube swapping and experimenting I've found thus far that the Svetlana in V1, Jan Philips 5751 in V2, and GT 12ax7-R in V3 really give it the most chime and fendery cleans I was wanting. I'm kind of stuck between the Mullard and the Svetlana in V1. They each sound a bit different but both great.
I'm a fan of the Deville now!


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Post subject: Re: Blues Jr iii consistently blowing power tubes.
Posted: Thu Jun 09, 2011 12:16 pm
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Yep, with the variety of tubes today, it is almost overwhelming trying to choose the right ones. Whether or not you use pedals, and what kind of pedals, can influence the choice also. I ended up with the GT (Sovtek 12AX7WC) preamp tubes in all three positions in my HRDvl, and I like using a POD in front of it (does great Marshall and Mesa sounds). I think that the Devilles are really the best of the HRd series. Too bad I can't move it very far without blowing out my knee....umph! In fact, the HRDlx doesn't go anywhere anymore for that same reason. So far, I can still carry the BJr around with me....but I have to make a second trip to carry in a guitar, both together are almost too heavy. :lol:

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