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hum?
Nov 13, 2007 16:04:35 GMT -7
Post by gtrplaya87 on Nov 13, 2007 16:04:35 GMT -7
i got a 66 brand new out of the box last week. loved it. i ended up having tube problems and i got new tubes from dr.z. it started working again and then stopped. i decided to take the amp back to the store and get the route 66 display amp they had.
the amp sounds a bit different but still sounds great. the only thing is there is a very low level hum. even when the volume is all the way down with nothing plugged in. theres a small hum. i didnt notice this w my first 66.
is this normal or is there somthing wrong?
if this is normal then its no biggy. i just want to make sure there is nothing wrong.
thanks
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hum?
Nov 14, 2007 7:18:08 GMT -7
Post by iggs on Nov 14, 2007 7:18:08 GMT -7
Is the standby on or off?
My Route 66 will have a low level hum if the output tubes are not matched within 5 mA. (meaning if they are more then 5mA appart, the amp hums) I had a pair of GT KT66C that were almost 10 mA apart and the amp was humming. Put in some generic Shuguangs (same tube as GT) from Tube Store and they were within 2mA, hum gone.
Also, is the amp biased properly? It would hum if the tubes are biased so hot that they are red-plating.
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hum?
Nov 14, 2007 7:55:32 GMT -7
Post by dixiechicken on Nov 14, 2007 7:55:32 GMT -7
DC here!
The 12AX7 PI-tube - second from the left - if you're looking into the Route from the backside.
This tube should also be in proper condition - i.e. balanced - aka both triod-halves should track the same. If not this may also possibly induce hum.
Cheers: Dixiechicken!
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hum?
Nov 14, 2007 8:52:29 GMT -7
Post by gtrplaya87 on Nov 14, 2007 8:52:29 GMT -7
thanks. its only when the standby is on. i emailed drz and they said it was common to have a low level hum because of the two output tubes.
the problem is know absolutly nothing about tubes and biasing(i need to learn). i have no idea what 5mA means. what should i do about the hum? get new tubes? if so should i take it to get biased? the other problem is i live in the middle of nowhere texas. the nearest amp shop is 2 hours away in houston.
is there a way i can get tubes with the same # as the existing ones and get rid of the hum?
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hum?
Nov 14, 2007 9:08:48 GMT -7
Post by dixiechicken on Nov 14, 2007 9:08:48 GMT -7
DC here! When purchasing output tubes you should say/specify a matched pair. Then your tubes idle current (mA) will be within 2-3 mA range. That is usually close enough to warrant the term MATCHED and should reduce the hum. But if if you PI-tube is unbalanced then the PI-tube may drive the output tubes un-evenly - and you risk inducing hum yet again. Go to: taweber.powweb.com/biasrite/br_page.htmRead up on the Weber Biasrite tool and how it works. Biasing your amp is like setting the idle throttle on your car. Is has to be the right amount of rpm/or in this case milli-amperes to make your amp work right. The Route66 can be biased with an idle current between 40mA to about 26 mA. Most people prefer somewhere between 31-38 milli-Ampere. Cheers: Dixiechicken!
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hum?
Nov 14, 2007 9:20:43 GMT -7
Post by gtrplaya87 on Nov 14, 2007 9:20:43 GMT -7
awesome..would i need the br-2 (octal) or the br 2 (nine pen)? what type of tubes should i purchase. groove tubes?
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hum?
Nov 14, 2007 9:28:14 GMT -7
Post by iggs on Nov 14, 2007 9:28:14 GMT -7
thanks. its only when the standby is on. i emailed drz and they said it was common to have a low level hum because of the two output tubes. the problem is know absolutly nothing about tubes and biasing(i need to learn). i have no idea what 5mA means. what should i do about the hum? get new tubes? if so should i take it to get biased? the other problem is i live in the middle of nowhere texas. the nearest amp shop is 2 hours away in houston. is there a way i can get tubes with the same # as the existing ones and get rid of the hum? If you're not comfortable with diggin' into the amp yourself then you should definitely take it to a shop and make sure they put a closely matched set of tubes into the amp and then bias it properly. The general consensus is that the Chinese KT66 (brown base, GT KT66C) are the nicest sounding new production tubes right now and are what Doc uses in his amps. If you just get another set of Groove Tubes with the same # you could put those in without re-biasing but I'm not sure how close does GT matches their tubes ... I've gotten a few sets from them over the years and none were matched real close ... all were around 5 mA while the sets I got from Tube Depot and Tube store were around 2mA. I know they say that anything up to 10 mA is fine but I kinda thought they should match them more closely since that's a big part of their marketing pitch. I'm sure Myles will disagree ... ;D So, if you're comfortable with electronics and high-voltage circuits in general but never had experience in biasing an amp, then order yourself a Weber Bias-Rite, do some research and reading and bias away. If you're not comfortable with it at all, take a road trip to Houston and have an amp tech look at it, maybe you can tell them your out of town and see if they can do it while you wait, it shouldn't take more then 30 min to swap some tubes and bias the amp. Also, DC is right, the PI tube may be a culprit as well, I had one that was humming like crazy in the PI slot ... turned out to be a noisy 12AX7, a quick swap cured it.
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hum?
Nov 14, 2007 9:32:19 GMT -7
Post by iggs on Nov 14, 2007 9:32:19 GMT -7
awesome..would i need the br-2 (octal) or the br 2 (nine pen)? what type of tubes should i purchase. groove tubes? Octal. You don't need to get Groove tubes but can if you want to ... these are the same tubes from the same factory as GT KT66C: www.tubedepot.com/si-kt66.htmlJust tell them to get you a "mid-range" bias point (anything from 32-42) should be fine.
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hum?
Nov 14, 2007 10:48:03 GMT -7
Post by gtrplaya87 on Nov 14, 2007 10:48:03 GMT -7
i tried the 12ax7 switch and i didnt cure the hum. must be the power tubes.
i checked out the power tubes in my amp and they are JJ"S and they dont have a rating # on them. i think im going to go with groove tubes. they sounded good in my first 66. i guess i will get the 4-6 range? then i guess i will get someone to bias the amp(if you have to bias groove tubes). i think its 40 bucks at a place in htown.
if you guys have anymore "words of wisdom" just let me know let me know.
thanks
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hum?
Nov 14, 2007 11:13:35 GMT -7
Post by iggs on Nov 14, 2007 11:13:35 GMT -7
I'd suggest #6 from GT ... I have a set of #4 and the lowest I can set the bias is around 34mA, which is fine but the bias pot is all the way down in this case and it can't go any lower. GT #6 should allow for a bit more "room" on the bias pot.
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hum?
Nov 14, 2007 13:53:18 GMT -7
Post by dixiechicken on Nov 14, 2007 13:53:18 GMT -7
"gtrplaya87" - DC here! Check this link out on DR-Z website about biasing: www.drzamps.com/biasnotes.htmlToawards the end Doc talks about bising the Route using an ordinary digital Volt-meter. Cheers: Dixiechicken!
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hum?
Nov 15, 2007 7:33:00 GMT -7
Post by gtrplaya87 on Nov 15, 2007 7:33:00 GMT -7
awesome..would i need the br-2 (octal) or the br 2 (nine pen)? what type of tubes should i purchase. groove tubes? Octal. You don't need to get Groove tubes but can if you want to ... these are the same tubes from the same factory as GT KT66C: www.tubedepot.com/si-kt66.htmlJust tell them to get you a "mid-range" bias point (anything from 32-42) should be fine. i went went ahead and got those tubes and ask for mid-range 32 to 42. the first 66 i had got had way more head room. it didnt get dirty till around 10 or 11 oclock on the volume. (with the bass and treb at 12) this current one i have gets dirty pretty fast. id rather have a little more head room though. the question is: did the first amp i had have a normal bias(mid-range bias)? or is my current amp biased normaly(midrange)? because they sound much different? one had jj power tubes and one had Groove tubes. that could make a difference also i guess. let me know what yall think..or how its supposed to sound..with a mid range bias.. later
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hum?
Nov 15, 2007 8:20:39 GMT -7
Post by iggs on Nov 15, 2007 8:20:39 GMT -7
The "bias point" from Tube Depot is just a plate current draw measurement (from what I understand). The higher the draw (when the tube is tested), the "harder" the tubes is, meaning it will distort "later" when biased the same as a "softer" tube inside an amp.
The bias pot inside the amp has a range and some tubes might be out of that range on either side of the spectrum, depending on their plate current draw.
From what I can tell (at least on my '66) the GT tubes #4 are at the low end of that range and I can't turn the trim pot any lower then around 34mA. That's why I said to order a "mid-range" tube since I tried some with that range and there seemed to be plenty "room" to move on the bias trim pot.
Also, what that may mean is that if you get some tubes that are very "hard", like #9 on th GT range, you may not be able to bias them high enough (just guessing, never tried though).
If you want more headroom, in addition to output tube change, I'd suggest a lower-gain 12AX7 in the PI slot or even a 12AT7 (I think this is OK, you might want to check with Doc first).
The big difference in sound I believe comes from the fact that JJ and GT (Chinese) KT66 are different tubes in sound, spec and design. According to Myles, the JJ's are not a "true" KT66 but more like a reworked 6L6, still a good tube and works fine in Route 66, just not a "proper" KT66 like the Chinese ones which are supposed to be a copy of the old GEC tubes. I keep switching between the two sets in my Route '66 and the JJ's are tighter sounding with apparently more headroom while Chinese ones are richer and distort nicer when pushed.
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