frank9310
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Post by frank9310 on Apr 30, 2008 8:21:51 GMT -7
I bought a Route 66 about a year ago and love it. However, a couple days after buying it I read the thread not to us Tung Sol KT66 because of the steel band possibly grounding out on the tube socket. Darned if I didn't blow a power tube (came with Tung Sols) 2 days after reading that. It was the KT66 furthest towards the on/off switch.
So I take it to an amp tech who discovered that the diode or resistor (can't remember what he said) in the tube socket had been blown, perhaps by the steel band grounding out after I read him the Tung Sol warning by Dr. Z. So we pop a set of JJ KT66s in and a new (diode/resitor), rebias to 36ma and all is well. So last night I turn the amp on and playing a few notes and hear it start to deaden on a couple notes and then smell something burning above one of the power tubes. Next thing it stops working altogether. Then I turn it off and back on and it sounds about half power, thin and weedy.
So I warm it up and the same tube is red like the other no brighter or less bright but is cool to the touch while the other side close to the preamp tubes is too hot to touch. So the amp tech tells me it probably blew that resitor or diode I forget which but he said it sounds like a bad tube. Well he forgot that I had this same problem before because it's been a while but now I'm wondering, this is too coincidental for 2 tubes to just go bad all the sudden in that same socket. Any ideas what could be causing this problem? These KT66s are getting expensive in pairs! Thanks.
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Post by myles on Apr 30, 2008 11:06:33 GMT -7
Probably a blown screen resistor ... check the bottom side of the tube sockets and look for a burned resistor. Easy to fix and cheap. If you were near me I'd do it for free and I have tons of 470 ohm and 1k ohm screen resistors that are the most common Fender / Marshall ones and they are not expensive at all.
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frank9310
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Post by frank9310 on Apr 30, 2008 12:47:08 GMT -7
Thanks Myles. It is the screen resistor because it looks toasted but it's not so easy to find! I called Doc's place and the guy there told me it's a 1.5k 3 watt flameproof resistor. Nobody local like Radio Shack etc. has them so I need to order through Mouser or somebody who wants to charge some iminimum order fee. Sheez
Update: I just ordered 5 of them at $1.30 each and with all the surcharge stuff and shipping it came to $22! Now for the 3rd set of KT66 tubes in the last 5 months there goes another $70 on top the resistors and 3 bias jobs. So at this rate it's looking like about $300-500/year to feed this baby and keep it biased. Glad I didn't buy any of those $300-500 per set tubes or I'd really be bummed. Love the tone though and can't wait to see how these Chinese Valve Art tubes sound compared to the JJs. The guy at Dr. Z said the Chinese is what they've been using lately for the overall best tone and looks like they're made with the original tools of the G.E.C. company so that sounds like a plus.
Anyone know how to bias them? Should they also be at 36mA. I heard a while ago that the Shuguangs needed to be biased high to run at their best and if I'm not mistaken the Valve Arts, anything with a C on the end like KT-66-C, Sino, Shuguangs are all the same tube.
Here the part info if anyone needs it for the screen resistor:
Mouser #: 71-CPF3-B-1.5K Mfr. #: CPF31K5000BEB14 Desc.: 3W Flameproof Metal Film Resistors 3watts 1.5Kohms 0.1% $1.30 Each = $6.50 for Qty 5 ($22 Total with S&H)
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Post by myles on May 1, 2008 14:02:08 GMT -7
Thanks Myles. It is the screen resistor because it looks toasted but it's not so easy to find! I called Doc's place and the guy there told me it's a 1.5k 3 watt flameproof resistor. Nobody local like Radio Shack etc. has them so I need to order through Mouser or somebody who wants to charge some iminimum order fee. Sheez Update: I just ordered 5 of them at $1.30 each and with all the surcharge stuff and shipping it came to $22! Now for the 3rd set of KT66 tubes in the last 5 months there goes another $70 on top the resistors and 3 bias jobs. So at this rate it's looking like about $300-500/year to feed this baby and keep it biased. Glad I didn't buy any of those $300-500 per set tubes or I'd really be bummed. Love the tone though and can't wait to see how these Chinese Valve Art tubes sound compared to the JJs. The guy at Dr. Z said the Chinese is what they've been using lately for the overall best tone and looks like they're made with the original tools of the G.E.C. company so that sounds like a plus. Anyone know how to bias them? Should they also be at 36mA. I heard a while ago that the Shuguangs needed to be biased high to run at their best and if I'm not mistaken the Valve Arts, anything with a C on the end like KT-66-C, Sino, Shuguangs are all the same tube. Here the part info if anyone needs it for the screen resistor: Mouser #: 71-CPF3-B-1.5K Mfr. #: CPF31K5000BEB14 Desc.: 3W Flameproof Metal Film Resistors 3watts 1.5Kohms 0.1% $1.30 Each = $6.50 for Qty 5 ($22 Total with S&H) 36mA is a great bias point. You are also correct .... Sino = Shuguang = Valveart = GT KT66C are all the same other than the Sino factory which is really a group of co-op smaller tube factories use the same design but their QA is not always what it should be. But the bad ones should be weeded out during testing by the better tube vendors. The new Sovtek GEC Gold Lion reissue is looking to be a very nice tube and a number of folks have nice things to say about it. Another option for players is always nice.
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frank9310
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Post by frank9310 on May 1, 2008 14:20:41 GMT -7
Thanks Myles. I read on thetubestore site where John Templeton said in a review "You should be sure that your amp's power transformer has the capacity to handle the extra current draw. Bias these tubes hot for best results. While most tubes we tested were biased at around 60% of their rated plate dissipation, the Shuguangs sound very bright and crystalline in this range. Some may find it too bright. At 75% of rated dissipation, these tubes really provide that feeling of rolling thunder. If you want Country clean, bias them for 60-70%. If you need earlier breakup and a beefier sound then turn up the heat, but keep an eye on your power tranny." thetubestore.com/6l6templeton.htmlSo that said, is 36mA you suggest considered to be biased hot and/or in your opinion, is he correct in saying the Shuguangs run best hot? Thanks
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Post by Deleted on May 2, 2008 8:32:51 GMT -7
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Post by Brent @ Guitar Riot on May 2, 2008 8:43:08 GMT -7
The grid resistor is 1.5k and the screen resistor is 110 ohm. You have 2 screen resistors coming in the mail.
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frank9310
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Post by frank9310 on May 2, 2008 9:03:01 GMT -7
Thanks a million Brent! You the man!!
dguilluame: This is where I get confused and have had it explained multiple times but I see conflicting things said each time. Ok on the link you sent above, Myles says: [Biasing on the hotter side of the scale will give more clean headroom, a tighter amp. But, if you go too hot the amp will sound harsh and tube life will suffer. Bias too cold and the amp will sound grainy and not develop full power. The amp will have it's clean tones suffer too if biased too cold. If you stay at 50-60% based on tube dissapation (30 watts for a KT66HP and 25 watts for a Genelex) and based on plate voltage you will be in a great range. The difference between 450-470 plate volts is pretty slight when it comes to bias. So ... if we figure 460 plate volts as a good number we have .... For a 25 watt Genelex or GEC KT66 or Shuguang KT-66 460 V 25 W 40% 50% 60% 70% 80% 22 27 33 38 43]
However, on the tubedepot notes I posted above, it says [at around 60% of their rated plate dissipation, the Shuguangs sound very bright and crystalline in this range. Some may find it too bright. At 75% of rated dissipation, these tubes really provide that feeling of rolling thunder. If you want Country clean, bias them for 60-70%. If you need earlier breakup and a beefier sound then turn up the heat, but keep an eye on your power tranny]
So if biasing high as Myles says gives more clean headroom and the tubedepot says biasing Shuguangs in the 60-70% gives country clean but 75% gives the feeling of rolling thunder, that seems to be the opposite of clean headroom at 75%. So if Myles mA ratings are in alignment with what the tubedpot is saying, if I want that rolling thunder sound, then wouldn't I be setting the bias at 40mA to be at the recommended 75%? According to that, 36mA would put me in the 65% range which would put me in the bright and crystalline range correct or no?
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Post by benttop (Steve) on May 2, 2008 9:17:14 GMT -7
Sometimes you just have to try a few bias points and choose what seems to be working best for the tones you're looking for. As you've discovered, there are really no absolutes to the biasing game, only good general guidelines to go by. Once you're inside the guidelines, only your ear will tell you if you've hit a home run or not.
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Post by Deleted on May 2, 2008 9:24:20 GMT -7
Thanks a million Brent! You the man!! dguilluame: This is where I get confused and have had it explained multiple times but I see conflicting things said each time. Ok on the link you sent above, Myles says: [Biasing on the hotter side of the scale will give more clean headroom, a tighter amp. But, if you go too hot the amp will sound harsh and tube life will suffer. Bias too cold and the amp will sound grainy and not develop full power. The amp will have it's clean tones suffer too if biased too cold. If you stay at 50-60% based on tube dissapation (30 watts for a KT66HP and 25 watts for a Genelex) and based on plate voltage you will be in a great range. The difference between 450-470 plate volts is pretty slight when it comes to bias. So ... if we figure 460 plate volts as a good number we have .... For a 25 watt Genelex or GEC KT66 or Shuguang KT-66 460 V 25 W 40% 50% 60% 70% 80% 22 27 33 38 43] However, on the tubedepot notes I posted above, it says [at around 60% of their rated plate dissipation, the Shuguangs sound very bright and crystalline in this range. Some may find it too bright. At 75% of rated dissipation, these tubes really provide that feeling of rolling thunder. If you want Country clean, bias them for 60-70%. If you need earlier breakup and a beefier sound then turn up the heat, but keep an eye on your power tranny] So if biasing high as Myles says gives more clean headroom and the tubedepot says biasing Shuguangs in the 60-70% gives country clean but 75% gives the feeling of rolling thunder, that seems to be the opposite of clean headroom at 75%. So if Myles mA ratings are in alignment with what the tubedpot is saying, if I want that rolling thunder sound, then wouldn't I be setting the bias at 40mA to be at the recommended 75%? According to that, 36mA would put me in the 65% range which would put me in the bright and crystalline range correct or no? One man's clean is another man's distorted tone. "Use your ears" and you'll find what you prefer. +1 for benttop's post.
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frank9310
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Post by frank9310 on May 7, 2008 7:51:25 GMT -7
The grid resistor is 1.5k and the screen resistor is 110 ohm. You have 2 screen resistors coming in the mail. Brent thank you so much for sending those! You are the man! I received them and am back up and running like a bear now thanks to you!!! Also, thanks so much for your great advice about using the Chinese tubes and how you explained the difference between the 3 types (Russian, Czech & Chinese)! I wish there was somewhere on the Z site at how well you explained that all. The Chinese tubes are made using the same tooling as the original UK made G.E.C. tubes and are truly a work of art with hand blown glass and sound like rolling thunder! I was amazed at how fantastic they sound and how pretty they are! www.jacmusic.com/valveart/intro.htmDr. Z Rocks in service!!!!!!!!!!
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Post by myles on May 21, 2008 14:11:59 GMT -7
The grid resistor is 1.5k and the screen resistor is 110 ohm. You have 2 screen resistors coming in the mail. Brent thank you so much for sending those! You are the man! I received them and am back up and running like a bear now thanks to you!!! Also, thanks so much for your great advice about using the Chinese tubes and how you explained the difference between the 3 types (Russian, Czech & Chinese)! I wish there was somewhere on the Z site at how well you explained that all. The Chinese tubes are made using the same tooling as the original UK made G.E.C. tubes and are truly a work of art with hand blown glass and sound like rolling thunder! I was amazed at how fantastic they sound and how pretty they are! www.jacmusic.com/valveart/intro.htmDr. Z Rocks in service!!!!!!!!!! Just as a side note .... the KT66C is NOT made on the same tooling as the GEC originals. They are of very different design if you ever take one apart and look at the grids, spacing, an materials as well. And .... nobody makes hand blown glass bottles, they are made on production machines just like cheap water glasses.
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frank9310
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Post by frank9310 on May 22, 2008 7:50:31 GMT -7
Interesting. So you really can't believe everything you read from the tube makers or sellers. Thanks!
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Post by Phil (aka Phil) on May 23, 2008 4:11:56 GMT -7
On thing's for sure though- just because the glass is made on a production line doesn't mean there's not some cool glass to be had out there. The JJ factory has some cool glass in their tubes (as Myles has said before). I was pretty shocked how heavy the glass is in the JJ KT77's and 6V6's I ordered. It's really nice and thick.
And, the KT77's sound awesome!!! The 6V6's aren't bad either if you don't mind the fact that they have a more midrange like a 6L6.
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frank9310
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Post by frank9310 on May 23, 2008 4:44:47 GMT -7
I did like the sound of the JJ KT66s though now I hear they are more like a 6L6 in design than a KT66. They seem to have a heavier glass like you said than the Chinese ones so if the JJs blew in a couple of months how long do the Chinese ones typically last? Does the glass thickness have much to do with the tube life expectency?
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Post by Phil (aka Phil) on May 23, 2008 6:37:47 GMT -7
The glass thickness doesn't have anything to do with the tube's life expectancy (as long as the glass doesn't get so thin that the tube loses vacuum, and you'd know that real quickly!)
The original KT66's made my Genelex and G.E.C. in England were rated at thousands of hours when used within their designed parameters. The way Dr. Z uses 'em (correct tube-to-tube spacing, plate voltage, plate dissipation, etc.) they would indeed last a very, very, long time.
Every tube made in the last 10 years that purports to be a KT66 is different than the "real thing" to varying degrees. A lot of them are just 6L6 or KT88 type guts in a KT66 looking bottle. Some are closer to the "real thing" than others, but they all sound different.
I've got a few sets of original G.E.C.'s in addition to a good supply of Valve Arts and two sets of GT KT66HP's. I've tried all three in my Route 66. I like them all for different reasons. The NOS G.E.C.'s are the best; they are the smoothest and clearest with the tightest bass and most complex mids. The GT KT66HP's (no longer available) are my second favorite; they have a thicker midrange and a slightly less bright and clear top end but are the most like the G.E.C.'s. The Chinese Valve Arts are the brightest sounding ones; they have a little of the clear "6L6" sound with a fatter midrange.
I haven't heard a lot of these "newer" tubes like the Tung Sols and JJ's so I can't comment. I do know that the chemicals, materials, and quality control used in manufacturing a tube are critical to the sound quality of any tube. These newer Russian and Chinese "KT66"'s seem to be all over the map in quality.
I would also change your rectifier to a NOS one like the "mislabeled" 5AR4 from Mike @ KCA NOS tubes.
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frank9310
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Post by frank9310 on May 23, 2008 12:34:45 GMT -7
Interesting info! Thanks a lot Phil! None of those tube places tell you anything like that. They all seem to claim to be exact replicas of original NOS or use original tooling, etc.. I put the JJ GZ34 back in and it sounds ok now with the Ruby KT66s I have one biased at 38.5 and the other at 36.5 so it sounds pretty good now.
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Post by Jim @94 Amps on Jun 16, 2008 20:27:37 GMT -7
I always bias them at 36mA, and we are currently using the KT-66C from GT. Sounds like you got it biased up and ready to rock!
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