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Post by brupri on Jan 6, 2012 9:50:47 GMT -7
There are JJ 6L6 GC for power, JJ GZ34S for rectifier, with the stock pre tubes. I purchased this used and it sure sounds great. Are re-biased 6L6 tubes interchangeable with the KT66s? Assuming I want to find some KT66 to put the amp back to stock, is re-biasing all that's needed or has something else gone on here?
Thanks, BruPri
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Post by randalp3000 on Jan 6, 2012 10:24:28 GMT -7
yes and yes
good luck rp
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Post by brupri on Jan 6, 2012 10:41:36 GMT -7
"yes and yes" yes-rebiasing is all that's needed or yes-something else has gone on here?
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Post by Deleted on Jan 6, 2012 11:28:33 GMT -7
6l6's are interchangeable and a re-bias is all you should need.
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Post by Deleted on Jan 6, 2012 11:29:40 GMT -7
Try the Gold Lion KT66. Very nice tube.
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Post by zdogma on Jan 6, 2012 12:59:25 GMT -7
Better with the KT 66's. Very easy swap.
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Post by randalp3000 on Jan 6, 2012 13:22:43 GMT -7
"yes and yes" yes-rebiasing is all that's needed or yes-something else has gone on here? yes... rebias
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Post by brupri on Jan 6, 2012 13:54:52 GMT -7
Thanks all! I did purchase some Golden Lions as well as an Amp Head Dual Bias tester which should work fine with my VOM. Another thing I noticed is that V2 is a 12ax7, the sticker on the inside of the case indicates originally a 5751. Docs website also refers to a 12ax7 so somewhere along the line (my amp is a 2008 anniversary) different tubes must have been specified. Anyone else running a 5751? I would imagine there would be a bit less gain...
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Post by prspastor on Jan 6, 2012 14:41:52 GMT -7
Just a little less overdrive if you had that 5751 in there. My Route 66 came stock with: EF86 (=C=) 12AX7 (Sovtek LPS) Gold Lion KT66 JJ5U4 Since then, I've replaced the JJ 5U4 with a NOS GE 5U4 as the JJ was buzzing in a funny way/leaking voltage. I'll keep the 12AX7 in there because I need my 66 to break up as soon as I can get it too. She's a loud amp! Doc has re-thought his rectifier choice on the Route 66 here recently and has settled on a 5U4 instead of the 5AR4. There is much more note bloom, sweetness, and earlier overdrive with a 5U4 in there. When you install those KT 66 in there, I'd swap in a 5U4 too and then do your rebias. You can get NOS 5U4 from KCANOSTubes.com for $30 or so. It'll probably last decades if not the life of your amp so it is a worthy investment. I'll echo what everyone else has said... KT 66 and 6L6 are swappable. The KT 66 is the Euro version of the 6L6 and is kinkless on it's power graph = smoother response. Very nice, deep tube that breathes your notes into the speaker. If you have the 6L6 in there, Doc has said that it will sound more tweed-like. I think that with the KT 66, the amp sounds more Bluesbreaker - but with thump.
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Post by brupri on Jan 6, 2012 18:56:53 GMT -7
prspastor-invaluable post, if I go with the NOS Sylvania military grade 5U4G/B from KCANOSTubes, do you know what my target bias voltage would be for the KT66?
Many thanks!
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Post by prspastor on Jan 6, 2012 22:17:54 GMT -7
With my 5U4, I read a plate voltage of about 410 volts. The KT66 Gold Lion is a 25 watt tube... So 25 watts / 410 volts times 60% dissipation is around 35 milliamps per tube. So I'd say somewhere between 32 and 36 milliamps is a good starting point for your idle bias setting. Adjust to what sounds good to you in that range. Your bias tester probe probably will read in millivolts for your multimeter. But it is read over a 1 ohm resistor, so 35 milliamps = 35 millivolts. Just a FYI in case you get confused that you are reading in millivolts.
Enjoyand welcome to the club! I'm here all the time if you need more help.
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Post by Deleted on Jan 7, 2012 2:19:14 GMT -7
Just a little less overdrive if you had that 5751 in there. My Route 66 came stock with: EF86 (=C=) 12AX7 (Sovtek LPS) Gold Lion KT66 JJ5U4 Since then, I've replaced the JJ 5U4 with a NOS GE 5U4 as the JJ was buzzing in a funny way/leaking voltage. I'll keep the 12AX7 in there because I need my 66 to break up as soon as I can get it too. She's a loud amp! A trick I used, besides what you mention above, was to bias the gold lions at about 70-75% dissipation. It allowed me to get the tones I was looking for with the volume at 1:00 o'clock instead of having to run it at 3:00-5:00 o'clock. Probably not much of a difference in db, but it I thought it helped. The Gold Lions stood up nicely, too.
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Post by brupri on Jan 7, 2012 10:39:50 GMT -7
Doug thanks for the tip, now I'm curious and to be frank, I'm sure remedial electronics classes might be in order! I get hooking up the meter and setting a pre-defined voltage, in the mean time, share with me please, how does one go about achieving "70-75% dissipation" when adjusting bias to a target voltage?
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Post by Deleted on Jan 7, 2012 13:43:42 GMT -7
Doug thanks for the tip, now I'm curious and to be frank, I'm sure remedial electronics classes might be in order! I get hooking up the meter and setting a pre-defined voltage, in the mean time, share with me please, how does one go about achieving "70-75% dissipation" when adjusting bias to a target voltage? I use the voltage reading from pin three of the weakest of the output tubes. Then I plug the proper numbers into lines 6 and 7 on Myles Rose's excel sheet (I'll explain how to get that in a minute) and then I adjust the bias using the shunt method (extremely dangerous). To get Myles' Anode Loading Chart go here www.guitaramplifierblueprinting.com/index2.htmlAt the top right of that page you'll see a red line just above the picture of Myles and his friend Loni Specter. Either right click and save image or left click and save file. The Gold Lion is a 30 watt tube so after you input the data on line 7 (plate voltage input on line 6) either press enter or left click on line 17. The "Heat Meter" at whatever % is the mA that you want to see on your volt meter. This link has the info for biasing your amp. www.duncanamps.com/technical/lvbias.html Any of the methods will work. If you don't have basic electronics knowledge you should let a tech do the work. Just tell them what you want and they should be able to help. If not find a new tech. Good luck and be safe.
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Post by brupri on Jan 7, 2012 13:52:03 GMT -7
Thanks Doug! In the interest of continuing my role as father to my family, I will defer to a qualified tech or simply be satisfied with the preliminary adjustment using the tools I have. Much appreciated all!
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Post by prspastor on Jan 7, 2012 17:52:00 GMT -7
I thought Myles said the golden Lions were 25 watt tubes... Although I'm certainly not trying to argue at all. I know some KT66 are 30 watt tubes. Brupi, the way you figure out how to get 70% dissipation is through a simple formula. You take the max wattage of the tube and divide it by your plate voltage. Then you multiply that number by .6 for 60% dissipation, .7 for 70% dissipation. Etc. When you set the bias on an amp, what you are really doing is setting the idle - like on a car. The hotter you run that tube at idle, the warmer it will sound, the hotter it'll run, and the quicker it's life will be. So. if your typical Route 66 with a 5U4 rectifier has about 410 volts on the plates (you measure this from pin 3 to the chassis using DC volts on your multimeter). you divide 25 watts by 410. That gives you 60 milliamps at the maximum dissipation of each of your tubes. We don't want to run those tubes wide open, we want to set them at an idle that will extend tube life and give you good tone. Myles often suggests 60% dissipation for the Route 66, although Doug has found 70% works really well for him for the tone he is after - so you see that there is a nice range you can bias in. So let's set that idle... so we take that number above - 60 milliamps - and multiply it by .60 (60%). You'll get 36 milliamps as your idle current. You can set your amps idle currant many different ways. You can do the shunt method, which is measure from pin 3 of the KT66 to the center tap of the output transformer - the place is on the multi-capacitor , although I don't remember the color of the wire... When you do this, you need to have your multimeter in DC amps, NOT volts. You then monitor the milliamp reading and turn the bias pot on the inside of the amp until you get the 36 milliamps. That method above is very dangerous as you are shunting high voltage. You also need to make sure your meter can handle 410 volts. My Fluke will handle 600 volts... I use aligator clips and attach on to the test points before I turn the amp on. Please be careful with this method. The other method is to buy a bias probe of some sort. This is a small devide you plug in between your power tube and your amp chassis. You then plug that device into your multimeter and read the milliamps. Same procedure, you turn the bias pot until you have a reading of 36. This is much safer, although you still have the chassis open and are exposed to high voltage in those big filter capacitors. Make sure that when you take the chassis out, don't accidentally roll your finders under and into the chassis and touch a wire. If you don't want to measure plate voltage and work with the formula, just bias your amp with a bias probe to somewhere between 32 and 37 milliamps. You'll be in the ballpark and ready to go. Enjoy! (sorry for the long missive) John
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Post by smolder on Jan 7, 2012 18:05:21 GMT -7
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Post by Deleted on Jan 7, 2012 19:14:36 GMT -7
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Post by brupri on Jan 7, 2012 19:20:45 GMT -7
Thanks all! The biasing content should be made a sticky under the appropriate amp or tech category (if not already...) It's kind of odd that whenever I try to do a Z-Talk website search, it usually gives me some kind of "excuse" why it can't find the information I'm looking for! It usually works better to Google the question and find the hits hidden in Z-Talk that way.
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Post by prspastor on Jan 9, 2012 13:30:13 GMT -7
Thanks Doug for the correction.
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Post by Deleted on Jan 9, 2012 18:07:48 GMT -7
Thanks Doug for the correction. Glad I could help. The truth is I didn't know either. If it wasn't for Myles I'd still be thinking they are 25 watts.
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