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Post subject: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Junior
Posted: Mon Dec 19, 2011 10:12 pm
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My Blues Junior NOS (modded) had Groove Tubes branded Sovtek tubes in it when I bought it, and I've been liking the sound of those pretty well.

Tonight as an experiment, I decided to put in the set of JJ electronics that I bought as a backup, and dag, did the JJs sound awful. They were all throaty, bright, and harsh. I guess at ~$50/set (3 ECC83 S, 2 EL84) you get what you pay for?

I've always heard that different preamp tubes have different sound characteristics, but I never expected the difference to be so, well, different.

I guess I'll get a backup set of Sovtek GTs (the "R" variety).


Blues Junior owners: What tubes do you like in your amps?

Do you ever buy a single 12AX7 from a manufacturer just to try it out in the V1 socket?


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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Mon Dec 19, 2011 11:34 pm
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Did you happen to check the idle bias of the JJ's? And how does this compare to the Sovteks?

As far as EL84 go.. hard to beat a Sovtek. Esp the EL84M (aka 6N14P-EV).


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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Tue Dec 20, 2011 2:28 am
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I read that a goog mix to do ; different brabd of 12AX7 / ECC83 give the best of each. This make sense for me.

+1 BMW2002Ti , a bias check is a must with new output tubes


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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Tue Dec 20, 2011 6:22 am
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BMW2002Ti wrote:
Did you happen to check the idle bias of the JJ's? And how does this compare to the Sovteks?


No, I didn't re-bias the JJ power tubes, but I did notice that most (if not all) of the original Groove Tubes/Sovtek sound returned by simply putting the original V1 preamp tube back in. Hence my question about whether other Blues Junior owners ever buy a single 12AX7 to test out in the V1.

The amp now has all the original set back in place.

One of the mods I did was to put in Billm's bias potentiometer. Maybe sometime when I'm bored, I'll play with the bias and see what that does to the sound of the amp. The bias voltage is currently set according to Billm's recommendation (don't remember what the value is off-hand).


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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Tue Dec 20, 2011 7:07 am
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mw13068 wrote:

The bias voltage is currently set according to Billm's recommendation (don't remember what the value is off-hand).


Bias voltage ( If you mean the bias negative voltage applied to the power tube grid and not the current , miiliamps, at the tube's cathode ) it COULD BE NOT the same for another set of tube,


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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Tue Dec 20, 2011 7:31 am
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stratele52 wrote:
Bias voltage ( If you mean the bias negative voltage applied to the power tube grid and not the current , miiliamps, at the tube's cathode ) it COULD BE NOT the same for another set of tube,


Yep. I realize that, but the preamp tube (V1) by my experiments is the culprit in this case since the amp sounds fine with the JJ power tubes and the GT/Sovtek preamp tube in V1.


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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Tue Dec 20, 2011 8:22 am
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Hi mw13068,

If you set the voltage drop across half of the OT primary to the Billm recommended setting, then you did set the bias, that's just one way to check it if you don't have a bias probe (which is fine). This must be done with each new set of output tubes, as mentioned. As far as preamp tubes, they can make as much of an impact on sound as the output tubes, and even more of a difference if you use very low gain preamp tubes. I tried several types of preamp and output tubes (Sovtek, JJ, EH, Ei, Tung Sol, RCA, GT, 7189s), and ended up with GT EL84 S output tubes and GT 12AX7 (Sovtek 12AX7WC) in preamp (V1, V2) and PI (V3), this combination sounds great. I also installed the adjustable bias pot as I felt that the stock bias was way too hot. I am using the tube damper rings to dampen the natural ring of the tubes, and partly for preventative measure, maybe the tubes will last longer, considering the pounding that they take in a combo.

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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Tue Dec 20, 2011 8:49 am
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Forgot to mention that the resistance of each half of the OT primary is about 100 ohms. If you divide the voltage drop across the OT primary half, by it's resistance (100 ohms), you'll get the Plate current for that output tube. Since both halves of the OT primary are the same resistance, the readings for one output tube will be nearly the same for the other. IIRC, I believe that the Billm setting will give about 8 watts of idle, just under 70%, which is a good range for the BJr. Plate voltage times Plate current equals idle wattage, and typically 50% to 70% is good, more towards the hot side for the BJr is better. :idea:

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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Tue Dec 20, 2011 9:46 am
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Like my knowledge of music theory, my knowledge of analog circuit analysis is rudimentary. In each case, I'm fairly proficient at the base mechanics, but most times don't fully understand what I'm doing.

I'll have to read more about bias current and how it effects the sound of the amp...

Thanks.


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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Tue Dec 20, 2011 1:28 pm
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Might want to check out this link, re: biasing and tone (with handy-dandy calculator--for HRD, but numbers can be manipulated for the BJr):


http://www.justinholton.com/hotrod/bias.html#byear


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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Tue Dec 20, 2011 1:36 pm
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IMO easiest calculator; Don't need to look for tube dissipation.
http://www.webervst.com/tubes1/calcbias.htm


By the way , biasing by ear !!!!!! Is it a joke ? Probably not but you need to be a magician or very lucky or you have a tube business
.
Good luck


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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Tue Dec 20, 2011 2:05 pm
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Stratele, I was thinking the author meant fine-tune to tone. I usually do this. Set the bias to low end of desired idle wattage. Then, tweak each individual output tube to tone. Each brand/make/model/year made kinda sounds slightly different.


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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Tue Dec 20, 2011 3:41 pm
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Blues Junior, not a Hot Rod Deluxe. The Justin Holton site is nothing about BJr, and the calculator won't work as the pin numbers are different, as well as the resistor designations, and there is no test point on the BJr. :idea:

Biasing, or fine tuning by ear is funny to say the least, the bias adjust isn't a tone knob. As we've all seen on this forum, biased wrong may sound good until your Plates start glowing red, and melt-down possibly damaging the amp also. :idea: On second thought, it isn't funny at all, it's sad.

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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Wed Dec 21, 2011 3:09 am
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BMW2002Ti wrote:
Stratele, I was thinking the author meant fine-tune to tone. I usually do this. Set the bias to low end of desired idle wattage. Then, tweak each individual output tube to tone. Each brand/make/model/year made kinda sounds slightly different.


You probably right BMW2002Ti, is not clear . The author must say that AFTER mesuring bias, fine tune with ears. That what I do myself . But I 'll be sure before bias is not too hot to damage tubes.

But how many people don't know how to mesure bias will play with their bias pot by ears after readind that ?


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Post subject: Re: Groove Tubes (Sovtek) vs. JJ Electronics in my Blues Jun
Posted: Wed Dec 21, 2011 3:10 am
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shimmilou wrote:

Biasing, or fine tuning by ear is funny to say the least, the bias adjust isn't a tone knob. As we've all seen on this forum, biased wrong may sound good until your Plates start glowing red, and melt-down possibly damaging the amp also. :idea: On second thought, it isn't funny at all, it's sad.


+1 Shimmilou


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