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Post by edoetsch on Jun 29, 2007 8:52:52 GMT -7
I am worried I bought a pair with a rating that won't work well with my Route 66 The number on the carton is 48. The pamphlet that came with it says 48 is the "actual plate current we measure". Remembering back to purchasing them from theTubeStore.com I don't remember being asked for a rating. Will these be close to the GT #6's that the Doc recommends?
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Post by zdogma on Jun 29, 2007 9:06:33 GMT -7
I am worried I bought a pair with a rating that won't work well with my Route 66 The number on the carton is 48. The pamphlet that came with it says 48 is the "actual plate current we measure". Remembering back to purchasing them from theTubeStore.com I don't remember being asked for a rating. Will these be close to the GT #6's that the Doc recommends? Any rating should work as long as you rebias. Might sound a little different but it'll probably sound good.
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Post by edoetsch on Jun 29, 2007 9:08:38 GMT -7
(Rubbing hands together like Mr. Burns)... "Excellent!"
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Post by nitehawk55 on Jun 29, 2007 12:21:38 GMT -7
When you order from the tube store you can specify you want a GT rating of whatever or just say you want tubes that will break up at a specified volume and just put that in the message box . I got a pair of Saratovs from them too but specified a 3-4 on the GT scale and lower volume break-up , mine are a #28 rating .
They should be fine but you might want to email them and find out how stiff these will be . I don't think their 48 rating has anything to do with your recommended bias setting but I'm guessing these may be very stiff .
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Post by iggs on Jun 29, 2007 15:39:29 GMT -7
The number from the Tubestore relates to the plate current draw for each tube. I order around 35 when I get them from Tubestore because I ordered a pair of Saratov once from them and could not bias the amp low enough ... I think they were around 50 ... not sure though.
Not to worry, the guys from Tubestore will take those back if they do not work out. Just tell them if you need a higher or lower number depending on how far the bias goes. My bet is that you might not be able to bias it low enough ... just a wild guess though.
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Post by nitehawk55 on Jun 29, 2007 17:23:43 GMT -7
Iggs , how are you liking those JJ's ? , I haven't tried mine yet .
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Post by iggs on Jun 30, 2007 20:18:15 GMT -7
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Post by myles on Jul 6, 2007 16:59:35 GMT -7
I am worried I bought a pair with a rating that won't work well with my Route 66 The number on the carton is 48. The pamphlet that came with it says 48 is the "actual plate current we measure". Remembering back to purchasing them from theTubeStore.com I don't remember being asked for a rating. Will these be close to the GT #6's that the Doc recommends? That number means nothing as the plate voltage and bias are not known. But .... that sounds like a mid range number off something like a maxi matcher so they should bias up fine and dandy.
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Post by edoetsch on Jul 9, 2007 10:42:16 GMT -7
I emailed the tubestore and got the comment that the tubes I received are probably a 7 or 8 on the GT scale. He believes a quick bias adjustment will not show any noticable difference between these tubes and the GT #6's
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Post by dongiesen on Jul 13, 2007 21:12:49 GMT -7
I just received some RFT EL84's from the Tube Store. Usually buy from Mike @ KCA. Anyway I specified in the comments section I wnated a matched pair with a GT equivelant of #6. Both the boxes have a #43 on them. So anyway since edoetesch says his said #48 and they responded with them being 7's or 8's I have to wonder if they ignored my special instructions. Maybe an email is in order but then they may just say what they think I want to hear
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Post by myles on Jul 14, 2007 10:39:12 GMT -7
You cannot convert a GT dynamic number to a static number. The GT number is based on where the tube distorts not just the idle draw. The only way you can do a close version of conversion is to have the latest or same batch of raw stock from which the tube was pulled (as each batch is different) and have access to the GT computerized GT stuff and run a side by side measurement. This will get you in the ballpark but there are many other factors considered on the GT scale.
The GT system also makes sure the tubes match under actual operation rather than at idle over the entire operating range of the tube. This is one reason that you might see a static match difference in a matched set at times of a milliamp or two but under operation on a curve tracer the two tubes will match perfectly across the entire amp's spectrum.
When you have numbers such as "43" you need to know what this number is. Is it plate current? Usually that is the case. But if it is plate current you need to know what the plate voltage setting on their test equipment was and also know the bias voltage used. Otherwise this number means nothing at all to the end user.
As a side note .... when I do tube tests I always use the original test spec settings as published in the RCA, GE, Sylvania, GEC, Mullard, etc., books. By the way ... all these specs were the same and had the same target.
As an example ... a simple tube matching unit such as the Maxi-Matcher will test a tube at 400 plate volts and -48 bias for 6L6 tubes. The numbers you see will be from 25-55mA or so. Using RCA book spec 250 plate volts is used with a -14.0 volt bias. A spec tube would produce 72mA. The tube is driven much harder as the bias is so much lower. This would be somewhat the same as testing at 500 plate volts and a -28 volt bias all things being equal. Most 6L6 amps have their bias at about -48v to -52v. -52 was the standard on many Fender amps and is the fixed bias of Mesa Boogie 6L6 amps.
Tesing at true book spec pushes the tube much harder into it's true operating range than the devices out there that seem to use higher plate voltages but with the higher bias keeps the tubes running at a much lower output. Less throw out when you do it that way.
Some folks think GT stuff is too pricy. Well, the labor time in testing is much higher as is their reject rate which is above 50%. The cost and upkeep on the testing equipment is insane as well as the calibration frequency to assure that a #5 tube from 20 years ago is the same as a #5 tube today.
For anybody in my general area .... if you even want your tubes tested just bring them to me. I do not accept mailing by the way. I will test them for free for you. I can also do this on afternoons, evenings and weekends as I have testing equipment at home. I can also tell you the true and actual gain of your preamp tubes which cannot be done with simple common testers including all of them that you see for sale on ebay. I can also tell you transconductance, current output, plate resistance and run curves on the tubes for true matching rather than just matching a number like transconductance which is what most folks do.
Once you know what the tubes in your amp are actually doing it is no longer a crap shoot at +/- 50% variability or more in the case of preamp tubes. You can then replicate your tone of you change tubes, move to a more gainy tube, less gainy one, tighter one, more easy to compress faster one, etc. This is what blueprinting is all about in some of it's areas .... knowing the specs and documenting what is actually going on in the amp.
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Post by dongiesen on Jul 14, 2007 13:25:34 GMT -7
Thanks Myles. I had a feeling buying these RFT's might be a crap shoot but then again I was hoping the KCA's and Tubestores, etc had some sense of common knowledge of each others ratings and such. I see it is a much deeper and more complex proposition. I normally use the GT EL84S but I must add that I have to have them shipped due to my location and the one thing I hate about that is that GT packaging where the set are banging together because of the 2 for container. Perhaps banging is too strong a word. Anyway lesson learned.
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Post by edoetsch on Jul 17, 2007 7:13:37 GMT -7
I also posted new but will comment here.
I put these guys in the amp, changed to an old 5U4 by Phillips that I picked up off eBay. Used a Weber Bias rite and biased around the top for the scale 36/38 mA. Sounds great. Seems a tad quieter than with the stock rectifier which is fine with me, I can get up to the grind a little quicker. I am assuming its the 5u4.
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Post by dongiesen on Jul 17, 2007 18:40:02 GMT -7
The only thing that bothers me now (though I'm electronically ignorant) is does any of the reputable tube sale sites like tube store, kca, eurotubes, etc. have the equipment that GT does. Something is telling me in my gut that buying properly matched or rated power section tubes is a crap shoot from any other source. I've purchased loads of preamp tubes and a rectifier or two from NOS dealers which I would imagine is a different story unless your a blue print your amp pro player but now I wonder more than ever about power tubes and the worthiness of their expertise
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Post by myles on Jul 18, 2007 17:59:35 GMT -7
The only thing that bothers me now (though I'm electronically ignorant) is does any of the reputable tube sale sites like tube store, kca, eurotubes, etc. have the equipment that GT does. Something is telling me in my gut that buying properly matched or rated power section tubes is a crap shoot from any other source. I've purchased loads of preamp tubes and a rectifier or two from NOS dealers which I would imagine is a different story unless your a blue print your amp pro player but now I wonder more than ever about power tubes and the worthiness of their expertise Only GT has the system they use (Mesa has a similar system) and only those two folks base the rating on where the tube actually distorts. I have some stuff on how different rating do things to power output in the rating area of my GAB website at www.guitaramplifierblueprinting.com/Rating.html
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