frank9310
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Post by frank9310 on Oct 30, 2007 8:14:02 GMT -7
In search for the perfect tone, tweaing a Route 66, I keep reading how some of the country pickers like the bias set around 32ma while others have set theirs to up to 40ma per tube.
When mine was set lower at around 32-34ma it seemed the notes were fatter and warmer but harder to get it to wail for feedback solos a'la Jimi.
Now, I've set it at 35-37.5ma and it seems to sustain better but the notes seem a bit more, should I say not as articulate with as much individual string definition?
Can someone describe in more detail what the tonal differences are with lower and higher bias settings as well as what's happening with the tubes. An amp tech told me that as you raise the bias, the plate voltage sometimes drops. In another place online, I read that Jimi favored his Marshall heads that had the highest plate voltage probably fr better feedback? So would that indicate that he had his tubes biased low?
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Post by Lefty on Oct 30, 2007 14:14:11 GMT -7
Regardless of what anyone says, I have always felt the recommended voltage applied to the tubes was best for longevity and tone.
increase bias= less voltage to the tubes decrease bias = more voltage to the tubes
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frank9310
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Post by frank9310 on Oct 30, 2007 16:52:04 GMT -7
Thanks Lefty. I also just read a pretty good article at www.tubedepot.com/whisbipo.html but that contradicts what I keep reading on here where several who favor country picking styles say that keep their biased low around 32ma and Ive read on Dr. Z's bias notes where he says "Bias too high and the amp will sound a bit harsh and distort too quickly, and will lose all focus at high volumes. If the bias is too low the amp will sound cold, brittle, and at higher volumes will have excessive crossover distortion, will sound dissident, and your guitar will sound out of tune." Yet on that link above, it's basically sayingthe higher the bias setting the more headroom and the lower it is, the easier it breaks up if you click the link and look at the fader chart. This is what's got me so confused.
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Post by Ed M. on Nov 1, 2007 10:13:27 GMT -7
Your talking about two different things here, one is the "hardness" of the tube and the other is setting the actual bias in a given circuit, so the information is not contradictory. Myles might be able to chime in and explain this better.
-ed
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Post by myles on Nov 1, 2007 10:29:25 GMT -7
Regardless of what anyone says, I have always felt the recommended voltage applied to the tubes was best for longevity and tone. increase bias= less voltage to the tubes decrease bias = more voltage to the tubes Bias is a negative voltage so to clarify .... If you increase the voltage in pin 5 of an octal based (EL-34, 6L6, etc) tube from say -48v to -50 volts the tube will run cooler and have lower idle dissapation noted, that is, on a bias tool you will see a drop from say 36mA to 32mA as an example. Running too cold ... the amp will be grainy and not develop full power in many cases. Running a tube too hot ... short tube life, amp will sound harsh. In a Marshall amp some people think that running the amp hot is a great way to go because they heard this somewhere. In reality, the hotter you run the less crossover notch distortion the amp produces and part of the characteristic magic of a Marshall is a certain amount of this x-over notch distortion being there. If too much is removed by running the amp hot then you also have an issue of the amp sounding harsh and sterile too. At high levels it might be workable but at moderate levels it will sound thin ... so now we have .... harsh, sterile, thin with short tube life and all kinds of extra heat in the amp we do not need.
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Post by myles on Nov 1, 2007 10:31:28 GMT -7
In search for the perfect tone, tweaing a Route 66, I keep reading how some of the country pickers like the bias set around 32ma while others have set theirs to up to 40ma per tube. When mine was set lower at around 32-34ma it seemed the notes were fatter and warmer but harder to get it to wail for feedback solos a'la Jimi. Now, I've set it at 35-37.5ma and it seems to sustain better but the notes seem a bit more, should I say not as articulate with as much individual string definition? Can someone describe in more detail what the tonal differences are with lower and higher bias settings as well as what's happening with the tubes. An amp tech told me that as you raise the bias, the plate voltage sometimes drops. In another place online, I read that Jimi favored his Marshall heads that had the highest plate voltage probably fr better feedback? So would that indicate that he had his tubes biased low? Plate voltage is one thing and bias voltage is another. They are not directly related other than when you have the amp biased way too hot you might see the plate voltage drop as you tax the power supply for the entire amp. Plexi Marshalls would vary between 450-600 plate volts and it was not the plate voltage that was the magic in the differences of some of these amps, it was many other factors.
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Post by Paul (TRANE) on Nov 1, 2007 10:51:57 GMT -7
I actually have done what Myles said and have to say he was 100% right. I had my 6545 head biased at ~65% (37mA at 430V Plate on EL-34[25W] tubes)....nothing radical or extreme though. I re-biased based on Myles' spreadsheet and advice to 60% (35mA at 430V Plate on EL-34[25W] tubes). The high end response was much smoother and not nearly as harsh as what I was experiencing before. Really made the amp fell much smoother and more dynamic to my ears. Follow the advice Myles gives and you can not go wrong.
Paul G.
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frank9310
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Post by frank9310 on Nov 6, 2007 7:56:41 GMT -7
Myles: I somewhat understand what you are saying but let's just say all I have is a bias tool, no ability to measure plate voltage, etc. and just go by the suggested bias range of 34-38ma per KT66 tube as Dr. Z suggests in the bias notes. So I pop the hot side tube in it and turn the trim pot to make it drop from i.e. 36ma down to 32ma. So if the tubedepot.com/whisbipo.html bias tool example says raising the ma of a tube gives more headroom and lowering it gives earlier breakup, are you saying the opposite to be true here? I mean leaving those other elements out of the equation, if I only have the bias tool to work with and the trim pot, is it safe to say that raising the ma will give me more headroom and lowering the ma will give me earlier breakup?
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Post by dixiechicken on Nov 6, 2007 8:36:27 GMT -7
DC here! I emailed Doc about this with three questions and received answers to those. ( thanks again Doc ) Doc:s replies are in yellow. Cheers: Dixiechicken
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Post by zdogma on Nov 6, 2007 9:39:56 GMT -7
DC here! I emailed Doc about this with three questions and received answers to those. ( thanks again Doc ) Doc:s replies are in yellow. Cheers: Dixiechicken I think it may be the VOLTAGE vs. CURRENT that is the source of the confusion here...
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Post by benttop (Steve) on Nov 6, 2007 10:58:48 GMT -7
I think it may be the VOLTAGE vs. CURRENT that is the source of the confusion here... Not surprising. OK, here comes my garden hose analogy. Voltage is a pressure. Your garden hose can have 120 psi or 10 psi. That's not saying anything about how much water flowed. Only the pressure. Voltage is a pressure. Current is actual flow. You can fill a bucket faster if there is more pressure, but the flow depends on the size of the hose doesn't it? That would be resistance. So in this discussion, you set your bias voltage to limit the cathode current. As you change the bias voltage, you get different cathode current. As the bias voltage becomes more negative, you get less cathode current. As the bias voltage gets more positive, you get more cathode current. Not sure if that helps, but the garden hose analogy usually brings out at least one "Ohhhhh...."
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Post by John on Nov 6, 2007 14:22:08 GMT -7
I think it may be the VOLTAGE vs. CURRENT that is the source of the confusion here... Not surprising. OK, here comes my garden hose analogy. Voltage is a pressure. Your garden hose can have 120 psi or 10 psi. That's not saying anything about how much water flowed. Only the pressure. Voltage is a pressure. Current is actual flow. You can fill a bucket faster if there is more pressure, but the flow depends on the size of the hose doesn't it? That would be resistance. So in this discussion, you set your bias voltage to limit the cathode current. As you change the bias voltage, you get different cathode current. As the bias voltage becomes more negative, you get less cathode current. As the bias voltage gets more positive, you get more cathode current. Not sure if that helps, but the garden hose analogy usually brings out at least one "Ohhhhh...." After all these years, someone finally explained it. +1 for Steve
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Post by woody on Nov 6, 2007 17:15:33 GMT -7
Myles: I somewhat understand what you are saying but let's just say all I have is a bias tool, no ability to measure plate voltage, etc. and just go by the suggested bias range of 34-38ma per KT66 tube as Dr. Z suggests in the bias notes. So I pop the hot side tube in it and turn the trim pot to make it drop from i.e. 36ma down to 32ma. So if the tubedepot.com/whisbipo.html bias tool example says raising the ma of a tube gives more headroom and lowering it gives earlier breakup, are you saying the opposite to be true here? I mean leaving those other elements out of the equation, if I only have the bias tool to work with and the trim pot, is it safe to say that raising the ma will give me more headroom and lowering the ma will give me earlier breakup? I'm definitely not an expert but I'm going to try to explain how I understand the link you provided. I think the Bias Point they are referring to is basically "grading" whichever tube you are purchasing..kinda like Groove Tubes assigns a number to the tubes that they sell. The Groove tubes rating scale goes 1-10...the lower the number the earlier the Powertubes will breakup...The higher the number =more headroom .... So I think that illustration from The Tube depot is their equivalent to a rating scale..helps them choose the correct powertubes for you according to your style of play. ie early breakup or more headroom...Now when you go to Bias your tubes in your amp thats when the actual principles that DrZ explains on his website applies.... hope this made sense. Joe
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Post by Telemanic on Nov 6, 2007 17:32:34 GMT -7
Yes the confusion regularly comes in using non equal terms like "biasing hot" and "biasing high" ...... they are not the same thing, .... in fact they are the opposite but so many times they are used in the same sentence because the terms "sound" alike. I know this has been covered technically but this is how i understand it all, hopefully if it helps anyone : The higher you bias a tube the lower the current will be, or colder it will idle, because as was explained the electrons jump off the negatively charged cathode, and want to race willy nilly to the positive plate or "anode". In a fixed/adjustable bias amp there is a negative voltage applied to the "grid" which is between the cathode and plate. It repels a certain amount of the electrons not letting them pass to the plate, thereby controlling the idle current of that tube. RAISING the bias voltage, which is negative, ... results in even less electrons passing to the plate, hence the tube runs colder yet. Of course then as logic would follow, if you lower the amount of negative voltage on the grid by "LOWERING THE BIAS", you allow more electrons to get thru to the plate because the grid has now become less negative/more positive. (Remember opposites attract). Now the tube is idling at a higher current and just like a car engine, if you set the idle to where it's really racing and then you step on the gas pedal, the engine will easily over rev with very little travel of the pedal! Which comes to the last item and that is that the Grid of the power tubes is connected to the plate of the previous tube stage, usually the phase inverter. It is connected by a coupling capacitor. These block the DC positive voltage, ( which is applied to the plate of each pre amp tube in the amp, just the same as the power tubes ) from passing thru the cap to the grid of the power tube. The coupling caps only pass AC voltage, which is your guitar signal. This voltage varies in amplitude as you play harder/softer etc. and when it hits the grid of the power tube it drives the grid towards positive which allows more electrons to flow to the plate increasing the "output" of the tube. Hence why they are called "valves". That action is like the accelerator in your car in the previous example, so if the tube is biased too low, ... IE. "HOT", You will quickly push the tube into clipping. Too much current is on the plate, and it may sound too fury and overdriven and lack articulation. Just the opposite is the tube is idling too low or cold, and it will not sound or perform right because it is not operating within it's design envelope. As long as you do not exceed the Max plate dissipation limits there is no right or wrong bias, just what sounds good to you. As Myles stated there are so many other things happening that are way over my head, but suffice it to say that with a basic understanding you can work with it usefully. The country guy's may like a lower MA or current setting because of the better articulation you may get from the amp not being too fury and overdriven too easily, ? just a guess.
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frank9310
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Post by frank9310 on Nov 6, 2007 17:43:56 GMT -7
Thanks. I did an ear test and called Doc Z today. What a great guy he is! Spent a good amount of time explaining to me how to adjust bias etc. and said that for the Route 66 were he mentioned it shoud be set at 475 volts and he said he was going to be changing that on the site because where he works on the amps is in a commercial building and his voltage is probably around 124 compared to my household voltage of around 114 (not exactly sure about the numbers but something like that). So he said instead of 475, with my residential voltage that number was probably more like 450. Well using the Eurotubes bias tool with on multimeter I set that at 36ma and the volts on the other red/white wire read at around 455 volts using another meter at the same time so Doc was right! So anyway, I tested playing it several times and he said another thing important. Most people (like me;-) think you can adjust that bias pot like a volume control but with KT66 tubes you really need to let it idle at an adjustment for a while until the tube gasses and output transformers, etc. stabilize at that new setting before you can determine how it really sounds playing it. So I set mine down to around 32ma while still having the bias tool attached, plugged in and played. I couldn't really tell much if it sounded like earlier breakup at 32ma or 40ma trying both and all in between, so I used a Fulltone OCD with the drive set on 1 o'clock and the notes were ringing out and getting ear peircingly thin and dying out at the 32ma setting. So I turned the trim pot to just about dead center (maybe a hair to the left of center) and it hit 36ma. Then I waited a minute or two after the tubes were already pretty hot to begin with and bingo! Unlimited sustain, clarity of the sustaining note which seemed to give it more body and wailing qualities (using the OCD). However, on the other end, when I turn it up to around 38ma or 40ma, the sustain stays constant, but it kind of loses some of the dynamics and tonal character and clarity plus it seemed to hit the ears harder. Thus, Dr. Z's recommendation of 36ma on other posts is spot on. I used a new set of JJ KT66 tubes with a JJ GZ34, NOS Telefunken EF86 and believe it or not, I tried about 10 preamp tubes. Starting with several JJ ecc803s with the gold pins, without, a Mesa tube, a couple of the GT-12AX7M Mullard re-issues and the Sovtek 12AX7LPS and they would all hold a decent note but fall flat on others, so I'd always have to play around the resonance spots or risk hitting these flat spots. Then I popped in a NOS RCA 12AX7 probably 30-40 years old and Shazaam! Instant unlimited sustain on all notes, beautiful overall tonal character, no spikes like those gold plated preamp tubes which claim to be more stable and have better this or that. It's these old tank built ones with none of those extras that did the trick! Just like the 66. Keep it simple! One other thing Doc did mention about the JJ KT66s is that they are a very stable tube so they do have lots of headroom, maybe too much for some who want an earlier breakup. So for the distoertion hounds, the Chinese tubes have more of that but are firecracker risks as well and do need the hotter bias to run well. I might just spring for a set of NOS GEC Gnealex clear glass, whatever I can find that uses the welded insides. A friend of mine who's a tube expert of sorts said: no tubes made today, including the Gold Lion reissues are made like the old GEC -Genelx tubes. The old ones had welded frames & todays are crimped. Also today they use different getters & gold plated parts etc to enhance things that really shouldn't be enhanced. The old tubes were stronger & last virtually forever . Crimped frames are less reliable & cannot hold up to the high voltages their designed for. So there you have it! Amp sounds great now!
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Post by Telemanic on Nov 6, 2007 18:11:03 GMT -7
Id say pop for em, i have 2 pairs of Grey glass, and they are amazing! Just be careful when ya buy them, The term "matched" is thrown around out there too much when usually they are not. Typically guy's,... even reputable sellers on ebay, will sell them as matched but they are usually only matched for Gm and not for ma or current. So be careful and ask. I bought a pair once of "matched Genelex" and put them in the 66 and could not bias them in. They were off by about 17ma! yet matched perfectly for mutual transconductance ( Gm ). Luckily he took them back (good seller). With tubes that rare 10ma is ok but preferebly less.
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frank9310
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Post by frank9310 on Nov 6, 2007 19:14:56 GMT -7
Woah! 10ma difference is ok? When I talked to Doc today he said usually matched is within 2-3ma so what does a difference like 17ma make when you only have one trim pot to set at i.e. 36ma on one tube and then the other tube is 17ma less?
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Post by Telemanic on Nov 8, 2007 11:25:11 GMT -7
With a single bias pot amp and a set of tubes that were 17ma off you would be running in a very unbalanced condition. It would not sound good at all and more importantly would be VERY hard on your output tranny, ... could very well trash it in a period of time depending on it's size and condition.
Yes 2-3 ma is considered a pretty good match, .... i was refering to tubes that have become as rare as say the Genelex KT66's when saying you could get away with 10ma. Some of these tubes are becoming VERY difficult to find sets matched to 2-3 ma or less. Certainly less would be better, but remember that back in the day there was not really any of this tube matching. We just bought new tubes and stuck em in there! The Nos tubes inherently had better tolerances so you were probably ok, but you can be sure that a lot of amps back in the 60's and 70's had sets that were 10ma off. Yes they would sound better with a better match. There are also proponents of NOT having perfectly matched power tubes as well as phase inverters. These folks say that perfectly matched cancels out 2nd order harmonics. There is as always, a strong debate over such things. But in general i think most folks would agree 2-3 is just fine.
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frank9310
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Post by frank9310 on Nov 8, 2007 13:06:24 GMT -7
telemanic: Wow! That is fantastic info! If I could give you a Karma I would! In your opinion what type of weirdness do you think would a very bad matched set of tubes sound like? Reason I ask is I've been trying to replicate Jimi's Monterey sound since he had KT66 tubes and a fuzz but his amp is sputtering and crackling in a musical way along with the fuzz sound. It almost sounds like a mismatched fuzz but is too drastic for it to be just that and it's not a bad cord. Songs like Wild Thing, etc. you can hear it in between the stops.
About phase inverters. Is there a Phase inverter in the Route 66 and or did they have them in the old days like on Jimi's Monterey stack? Are 2nd order harmonics what Jimi had lots of when he did his dive bomb wails like intro to Wild Thing?
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Post by dixiechicken on Nov 8, 2007 16:22:48 GMT -7
Yes the Route 66 have a Phase Inverter tube. All class AB amps and class B amps have one. That's the second tube between the big power tubes and the EF86.
It's the second tube from the left if you look at the Route head from the backside. The tube is the 12AX7 == ECC83 preferably with balanced triod halves.
Second order harmonic or even order harmonics in plural - is what the human ear tend to accept or experience as good distortion, Or be forgiving about to put it another way.
Odd order harmonics we usually do not experience as pleasing.
Cheers: Dixiechicken!
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frank9310
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Post by frank9310 on Nov 8, 2007 16:37:35 GMT -7
Dixiechicken! Ahh! THat explains it! Thamks a lot! Well didn't all of Jimi's amps have 12AX7 preamp tubes in them such as as the 1959 Super Lead and his JH100 KT66 Stack?
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Post by dixiechicken on Nov 9, 2007 3:28:49 GMT -7
DC here!
You should perhaps ask Myles about that or Dave Hunter - but....
It is possible of course - given that the 12AX7/ECC83 tube is one of the most commonly used pre-amp tubes.
Cheers: Dixiechicken!
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Post by Telemanic on Nov 9, 2007 13:04:32 GMT -7
Hey thanx for the Karma thoughts! ... Yeah, Jimi's rig is tough to track down the details. He would do some well, unorthodox things sometimes with his gear, and of course with the help of Mr. Mayer. So much of Jimi's sound, IMHO lies with the mans hands themselves! I know the moments that you speak of on the concert video, ... the ripping, tearing almost sputtering sounds he gets. Impossible to fully duplicate every nuance of his rig that night, or any other for that matter, but being kind of a fuzz nut at one time i can tell ya that much of it does lie in his "germanium" fuzz face and more importantly in his use of it! It really is an art or technique itself in really knowing how to get all you can out of a fuzz. So many guy's tend to try and use them like you would an O/D, and are disappointed and end up using them very little if at all. The key to a fuzz is in mastering the volume knob on your guitar! Watch most any video of Jimi, the 69'-70' new years eve Band of Gypsies is a great example, and you'll see that he rarely has the fuzz pedal off! He instead has all these shades of inbetween sounds, really pretty clean to all out screaming and never steps on the fuzz pedal once! I think the sounds you are seeking are the result of a Plexi "CRANKED" which as you know is not a real gainy amp, and his fuzz "on", but with his subtle mastery of the guitar volume knob. Obviously a lot more goes into the whole thing, but i feel thats the closest one could hope to get.
As for the tubes, yes Myles is the Man to ask about technical stuff for sure. But i can tel ya that power tubes that far off would not be the answer to Jimi's sound! Again back in the day, there were "magical" Marshalls and such, ... when in reality it was just that everything just kind of was in tolerance, a great output tranny, caps, tubes well matched etc. With tubes it would help to have well documented specs on each so you could put logic to why the amp sounds better or worse with various tubes swaps, ... but the reality is that most just have to experiment with "unknowns" and let your ears be the guide. I have amps that ive gone thru 10 or more 12ax7's until ive found the " magic " one. It will help you to listen to your amp and try to find what you'd like to change if anything, and then you can seek a "known" tube that has certain characteristics. At least then it's not complete blind trial and error! Best of luck!
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frank9310
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Post by frank9310 on Nov 10, 2007 9:36:37 GMT -7
Thanks Dixiechicken and telemanic! I agree that mastering the Fuzz is an art form! Especially using a germanium vs. the silicon used with Band of Gypsys. They have completely different dynamics. I'm liking using a Fuzz (either one) more and more with the 66 than an overdrive because there's no noisy-grindy sounding preamp stages so you can really dial in everything from clean to nasty with just a fuzz. With a Marshall JCM 900 that already has all those preamp stages and diode rectifier a fuzz just sounds mushy so I wind up using an OCD or some clean boost or distortion pedal but with the 66 the Fuzz sounds much more organic. Cleans up nicely and can overdrive with the best of them. When I use things like the OCD or GT500 they sound great but not as natural with the 66. telemanic: I must have spoke too soon. After exerimenting with around 10 different premap tubes from different manufacturers I wound up using the NOS RCA 12AX7 that gave me beuatiful breakup, dynamics and sustain. NOw a couple days later I'm noticing microphonic squealing at times. Could this the preamp tube or would it be the Telefunken EF86 or the new JJ GZ34 rectifier?
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Post by Telemanic on Nov 12, 2007 10:05:13 GMT -7
Hi Frank! Sorry ive been out for a couple o days. Cool glad to hear of the nice tones man! I go back and forth on liking Silicon vs. Germ! As for the squealing, almost certainly either the 12ax7 or the ef86. The Telefunken's are built incredibly, but the EF can do that, i had a nice sounding Mullard that went noisy on me. It's one of the reasons Doc has shyed away from making a Rt.66 combo. On the other hand it's nothing either to come up with a micro 12ax7 as well. I'm sure your already zoomed in on it by swapping each out and see. My fave tubes for the 66 ended up being an Amperex Holland EF, and a Telefunken 12ax7 for the PI. The tele's are known for there linearity and lack of a pronounced mid-range. That was key for me as i felt i needed to thin out the mids on the 66 a bit, ... it's the low-mid/mids that were clogging up for me, and the Tele helped huge, along with a set of grey glass KT's! The Telefunkens are also known for there huge output, they are really strong tubes!!
I also know what ya mean with the pedals, i did not like the OCD in my 66, in fact i tried tons of boutiques, .. Zen's, Eternity etc. and could not quite find what i wanted. The 66, to me anyway, is so thick that a lot of these pedals ended up sounding congested and almost like a blanket was over the speakers. I'll tell ya my secret weapon with that amp and others that make a nice crunch on there own: ..... an old Vintage yellow Dod 250 overdrive!! Not the re-issues, you have to be careful buying used and ask for a picture of the circuit board to be sure it's an oldie ( 80's ). Or send a re-issue to AnalogMan for about 75.00 he does an Excellent mod to original "Grey 250" specs. It is THE strongest most muscular O/D ive played, and oddly enough, by my definition anyway, THE most transparent and open sounding there is. IMHO, it has no equal in that amp! Peace man, talk later!
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