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Post subject: New power tubes in the Blues Jr.
Posted: Fri May 20, 2011 7:22 pm
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Changed the power tubes from JJ EL84 to the original Groove Tube EL84 and rebiased. The sound is warmer sounding with breakup a bit sooner but the output seems lower? Is this normal or are the original tubes a bit worn? I actually like the sound much better....

Any thoughts out there?

Beaubs

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Fri May 20, 2011 7:59 pm
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It could be a few things,but not all tubes are equal.Groove tubes have different ratings some tubes break up earlier then others, that is what's with there numbering system.A groove tube el84 is made different then a jj el84 but have the same specs and it's still considered a el84. I noticed you said you have a blues JR,how did you rebias this amp?


Also your tube could be worn


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Post subject: Re: New power tubes in the Blues Jr.
Posted: Fri May 20, 2011 8:13 pm
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I have found the same thing, the JJs do sound louder than the stock GTs, kind of a trade-off with the GTs having a warmer sound. You put a bias pot in your BJr recently if I remember correctly, right? :idea:

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Fri May 20, 2011 8:17 pm
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shimmilou wrote:
I have found the same thing, the JJs do sound louder than the stock GTs, kind of a trade-off with the GTs having a warmer sound. You put a bias pot in your BJr recently if I remember correctly, right? :idea:


Yes, I did put in a bias pot and then followed the instructions for setting the bias in the BillM instruction sheet.

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Fri May 20, 2011 8:25 pm
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shimmilou wrote:
I have found the same thing, the JJs do sound louder than the stock GTs, kind of a trade-off with the GTs having a warmer sound. You put a bias pot in your BJr recently if I remember correctly, right? :idea:



....by the way, thanks for your continued input Shimmilou, I always can count on you and other select Forum Members for solid reference information and experienced insight. :D

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Fri May 20, 2011 8:47 pm
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Glad to help. If you have the bias set at a more reasonable level than it was from the factory, the GT output tubes should last for years. In fact, the GTs are long lasting tubes even in the stock BJrs. :)

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Fri May 20, 2011 8:56 pm
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shimmilou wrote:
Glad to help. If you have the bias set at a more reasonable level than it was from the factory, the GT output tubes should last for years. In fact, the GTs are long lasting tubes even in the stock BJrs. :)



I am set between 3.2 - 3.4 volts with the TO20 transformer

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Fri May 20, 2011 9:17 pm
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Do you remember the idle wattage that you calculated, or even the resistance of the TO20? The TO20 has a different resistance than the stock tranny. :?:

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Fri May 20, 2011 9:23 pm
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shimmilou wrote:
Do you remember the idle wattage that you calculated, or even the resistance of the TO20? The TO20 has a different resistance than the stock tranny. :?:



Sorry Shimmilow I don't. You did ask this before and I never found the answer. The instruction sheet states that the transformer resistance is 100 ohms and a 2.4 volt drop indicates a 24mA of plate current. Then states that I should have 8 watts of idle dissapation and the Heyboer output transformer should be set at 3.2 to 3.4 Volts.

This means nothing to me other than I set the bias at 3.2 to 3.4 volts.

...does it make sense to you?

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Fri May 20, 2011 9:49 pm
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OK, the stock tranny is 100 ohms and will have 24 mA with a 2.4 volt drop (8 watts at 330 Plate volts). So the TO20 should have a higher resistance meaning a higher voltage drop for the same current (24 mA). If at 3.3 volts (averaged) on the TO20, assuming that the recommended voltage gives the same 8 watts idle, then the TO20 resistance would be about 137 ohms. Yes, 8 watts should give you much longer life for the tubes. Thanks. :)

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Sat May 21, 2011 2:52 am
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all this stuff confuses me. :roll: :cry:

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Sat May 21, 2011 5:39 am
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way cool jr wrote:
all this stuff confuses me. :roll: :cry:


I'm with you WCJ but that is why we have Arjay and Shimmilou!!!!! :D

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Sat May 21, 2011 7:19 am
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Beaubs wrote:
way cool jr wrote:
all this stuff confuses me. :roll: :cry:


I'm with you WCJ but that is why we have Arjay and Shimmilou!!!!! :D


indeed. :wink:

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Post subject: Re: New power tubes in the Blues Jr.
Posted: Mon May 23, 2011 3:11 pm
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I think your numbers are in the ballpark, my TO20 measured at 131 Ohms.

To get an exact calculation when you change tubes you should measure your plate voltage. (board location P3 to Ground)
Also measure the OT resistance (Ohms across board locations P2 to P3)

Then plug in the numbers assuming you are going for 8 watts dissipation.
Target Dissipation(8Watts) divided by Plate Voltage(P3 to ground) = Plate Current

Then using the Plate current obtained from the above and plug it and the OT resistance into the following:
Plate Current x Ohms across P2 to P3 = Voltage to set with trim pot (measured across P2 to P3)


WARNING HIGH VOLTAGES BE VERY CAREFUL.


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Post subject: Re: New power tubes in the Blues Jr.
Posted: Wed May 25, 2011 10:58 am
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Try some Telam EL84´s mate. I assure you will never look back. I didn´t. I´m using them along with JAN Sylvania 12AX7WA´s on the pre´s on my Pro Junior. Awesomeness!

This is its review from tubestore.com:

Quote:
Telam and Polam EL84 - Two wild and crazy tubes! I think for single coil guitars they are the best sounding tubes available. Fender amps love them. Pro Junior, Blues Junior two thumbs up. Mesa Boogie, VOX, Dr Z another two thumbs up. The midrange is very rich in harmonic content. JJ’s sound flat and one dimensional by comparison. The great mids transition into a smooth clear treble and the bass frequencies are solid with no flabbiness. I had a couple of players testing them and they had no problem in picking these tubes as their favorites. Numerous tube swaps were done and the boys would always be able to tell if Polam or Telam were installed.
From a construction standpoint there is more good news. They seem to have stayed very close to the original bottle specification. A lesson that a lot of tube makers have not learned. I’m convinced that the Telam and Polam tubes are out of the same factory. The bottles are the same, the spacers, pins and internal connections all look the same. The only difference is in the stamping of the plate. Telam has a ribbed plate that is spot welded while Polam has a smooth plate that is crimped. The coating on both looks identical. Microphonics or mechanical noise doesn’t seem to care about the construction methods as both are excellent. Picking one over the other is difficult because they sound so much alike. Both tubes sound great clean and both have a beautiful natural overdrive sound with bite and a good aggressive sound.


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