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Posted: Sun Sep 26, 2010 8:48 am
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shimmilou wrote:
Thanks kineman karma, bluesky636, and stratele52! I have only bought 3 JJ tubes ever, 1-6V6 S for my C600, and 1-matched pair of 6L6s to try in my HRDlx. The JJ 6V6 was only used briefly in the C600 (1-2 hrs total), I put the original back as I thought that the JJ was too bright in this instance. Then when I modified the amp I put the JJ back in and it started causing its own feedback, which I stopped by touching the tube. I guess that some tube dampeners will take care of that. The JJ "matched pair" of 6L6s were running about 5 mA difference in the HRDlx, I sent them back and got GT replacements which were running within 1 mA of each other. To be fair, I've even sent back "premium" tubes because of mismatched plate current. I have only ever sent back 1 GT tube, a 12AT7 that was horribly microphonic right out of the box.

I know that it would be wrong of me to conclude that the GTs are "better" than JJs based on this small sample size, but I see the same thing happen when others change to JJs and claim that they are better based on a skewed comparison (ie GTs sound harsh, but JJs sound better, even though the bias is way different between the two sets).

stratele52, I have gotten used to the mV vs mA discussions. We are all really talking about the same thing, just measuring a little different way. :) Just remember that mV measured at the Fender test point can be directly translated to mA. The test point is cathode current, which is always higher than plate current by about 10 mA for two tubes (5 mA per tube). I just do the translation in my head, kind of like translating French to English :lol: So it's all good. :)

Thanks guys, for taking the time to share your results, and your honest answers. I will do further testing, because the JJs are cheaper than GTs, and I want to get on the JJ fashion train myself. :lol: :D

Edit: Forgot about the BJr. That amps is biased so overly hot that it will eat any tubes that you put in it. I guess that the JJs sound much better as they are melting compared to the sound of the GTs melting. :lol: :lol: But, I ended up using a set of 7189s for the BJr. With the same bias for the 7189s and the GT EL84 Ss, I preferred the 7189s. :o


On the JJs that measured 5 mA different: It is my understanding that a 5 mA difference in bias current is acceptable. This is mostly due to tolerances in both the amp and tube construction. In that case, it is suggested to swap tubes between sockets. Sometimes this will bring the tubes into closer match. My JJs are about 1.5 mA different in bias current. I set things based on the higher of the two readings using my bias probe.

Regarding the GT 6L6s. I have read (but won't swear it is true), that they are not true 6L6GCs and are not rated at 30 watts max dissipation. Mine are Sovtek 5881WXTs. I can't find a tube chart for the Sovtek tube but this site has some good info. It looks like the Sovtek tube is only rated at 23 watts and hence should not be run as hot as a JJ 6L6GC.

http://www.jayskyler.com/guitar-gear-gu ... guide.html

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Posted: Sun Sep 26, 2010 9:11 am
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bluesky636 wrote:
On the JJs that measured 5 mA different: It is my understanding that a 5 mA difference in bias current is acceptable.... In that case, it is suggested to swap tubes between sockets. Sometimes this will bring the tubes into closer match.


5 mA out of 30 mA for the tube is over 16 percent, that's way too much difference, it should be closer to 5 percent difference. Yes, I swapped the tubes position and made sure that the difference stayed with the tube, not the circuit. I was hoping that the tubes were ok, I hate to have to return tubes, but these days it's a given, or a "crap shoot" as some have said.

bluesky636 wrote:
Regarding the GT 6L6s. I have read (but won't swear it is true), that they are not true 6L6GCs and are not rated at 30 watts max dissipation. Mine are Sovtek 5881WXTs. I can't find a tube chart for the Sovtek tube but this site has some good info. It looks like the Sovtek tube is only rated at 23 watts and hence should not be run as hot as a JJ 6L6GC.


Yes, I've seen that too, the GT 6L6 R (5881s) are 25 watt, but the GT 6L6 S are 30 watts, I used the "S" type because of that. Some sites show the 5881s as the same tube as the 6L6GCs, but I'm with you, I think that the 5881s are lower watts. :)

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Posted: Sun Sep 26, 2010 11:14 am
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shimmilou wrote:
Yes, I've seen that too, the GT 6L6 R (5881s) are 25 watt, but the GT 6L6 S are 30 watts, I used the "S" type because of that. Some sites show the 5881s as the same tube as the 6L6GCs, but I'm with you, I think that the 5881s are lower watts. :)


The GTs that came in my BDRI were relabled as 6L6-R.

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Posted: Sun Sep 26, 2010 12:54 pm
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Thank's blue sky. I hope Kineman do the samething than you for the bias.
I ,too, use the 1 ohms resistor on tube kathode and convert Millivolts to Milliamps. For bias, we should not talk about Millivolts but Milliamps . It is Milliamps go throught power tube for our use of calculate power.
Millivolts are applied to tube grid by the bias adjust pot or fixed resistor for change tube Milliamps for proper bias.
Sometimes I 'm not sure what people talk about. If they don't make mistake


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Posted: Sun Sep 26, 2010 12:59 pm
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+1 Stratele52, bias current shall be reported in mA (belle strat rouge); Also the power heated by the valve is the sum of Vpk*Ipk+Vg1k*Ig1k+... (other grills). As the kathode current is the sum and reported by the 1 Ohm to the voltmeter, if it is multiplied by the plate-kathode voltage we over-estimate a little the heated power, due to the fact that g-k voltage is lower.

however, good works for the mods. I'm curious for the Jensen. 8)

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Posted: Sun Sep 26, 2010 1:19 pm
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Thank's Tissan, my favorite Strat. I don'know how Fender name this color. It's a 1995 Am Standard, some kind of transparent red with lipstic (?) red on the sides. I see the wood thru the color if close enough.

Click on picture for big one


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Posted: Sun Sep 26, 2010 1:21 pm
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stratele52 wrote:
Thank's blue sky. I hope Kineman do the samething than you for the bias.
I ,too, use the 1 ohms resistor on tube kathode and convert Millivolts to Milliamps. For bias, we should not talk about Millivolts but Milliamps . It is Milliamps go throught power tube for our use of calculate power.
Millivolts are applied to tube grid by the bias adjust pot or fixed resistor for change tube Milliamps for proper bias.
Sometimes I 'm not sure what people talk about. If they don't make mistake


You say "to-may-to", I say "to-mah-to". Measuring 70 mV across a 1 ohm resistor is the same as measuring 70 mA through a 1 ohm resistor. One equals the other. Divide by 2 and you have the approximate cathode current per tube. Multiply that by the plate votage and you come up with power dissipated by the tube at idle. I think most of us here understand the relationships and if not, someone will teach them. :D

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Posted: Sun Sep 26, 2010 3:47 pm
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I know Bluesky that xxMV equal xxMA on 1 ohms resistor but when we talk about Bias it easier to use the right word and the bias is MA, Milliamp not Millivolts.


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Posted: Sun Sep 26, 2010 3:59 pm
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stratele52 wrote:
I know Bluesky that xxMV equal xxMA on 1 ohms resistor but when we talk about Bias it easier to use the right word and the bias is MA, Milliamp not Millivolts.


Use whichever you prefer. I am an electrical engineer by degree. I am comfortable using either term, depending on how the measurement was made. I am not going to beat anyone up because they measured xx mV across a 1 ohm resistor as long as they understand the relationships involved. If they don't, I will attempt to explain it to them. Ok?

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Posted: Sun Sep 26, 2010 6:16 pm
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stratele52 wrote:
Thank's blue sky. I hope Kineman do the samething than you for the bias.
I ,too, use the 1 ohms resistor on tube kathode and convert Millivolts to Milliamps. For bias, we should not talk about Millivolts but Milliamps . It is Milliamps go throught power tube for our use of calculate power.
Millivolts are applied to tube grid by the bias adjust pot or fixed resistor for change tube Milliamps for proper bias.
Sometimes I 'm not sure what people talk about. If they don't make mistake


The common term for measuring a bias in my neck of the woods is MV not MA... either way I agree with Bill, don't beat up on anyone purely because you say (to may to) and we say (to mah to) lol good one Bill :lol:

All technical aside lets talk about tone, are you ready for this Bill it's long winded.... :P

Since doing my mods I have completed 9 rehearsals and 7 shows with this little gem called Blues Deluxe Reissue.

One gig of significan't note that stands out, was a gig I did in Pt Augusta South Australia.

It is 330 kilometers and no not miles... :P from where I live in the big smoke.

Anyway for this road trip I was a bit hesitant on taking my New Twin Amp, so out came my BDRI...

We set up and sound checked in an old town hall which held 400 people on the night. The stage was tight so the BDRI was the right choice.

Ok, after the local country band played it was our turn to Rock N Reggae with my first band Kineman Karma. Original Works.

Using the BDRI we played a 1hr and 30 min set.

The BDRI handled really well giving me that clean headroom I needed for those Reggae Chops and when I needed that crunch for those solo's I got the break up just needed that I lightly accompanied by a TS-9 overdrive. Using this method I hear more Amp than pedals.

Ok for this set with the Reggae band, the amp held up well and I was complimented from the sound guy for my clean tone and crispy crunchy overdrives that put up clear note seperation.

With the same band members but different project I put up my Rock Blues band called Swamp River Band. Classic Rock, Blues, Modern Rock. ie; CCR, zz Top, Buddy Guy, SRV, etc etc..

Well this set was a rock solid 2 hrs and 30 min and we were stuffed after this show. Didn't complain about the pay $ though :D

Well my harmonica player in Swamp River Band was positioned near my amp, keep in mind he is also a big Fender head guitar player in the first band Kineman Karma.

Ok, during our Blues set he yelled out on numerous occassions when I was soloing screaming out "Hell Yeah"
he then grabbed me by my shoulder and yelled into my ear.....
"Great #$@*&!% Tone Man"....

I must admit I was pretty impressed and proud of my mods to this amp, considering it had to stand up and run hot for long periods of time without failure.

The show was a success with 400 people singing every word of my originals. They then whistled our ears off between every song with our party set... I would rate the show as being in my top 5...

With the BDRI I had no reliability issues, no tone issues, no struggling to keep up with the band level wise and I got nothing but positive compliments by everyone all round, there were a lot of other musos present.

With high regard to everyones tech knowledge here, all that said and Technical aside ie; MV / MA scrillyamps..... :roll: :lol:
Tone is the Master!!!!


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Posted: Mon Sep 27, 2010 10:40 am
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Rock on kk!

My only audience is my two Golden Retrievers, Pete and Annie. And they usually leave once I hit the first power cord or do a high pitch double bend. :lol:

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