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| Tubes have a whole language of their own.
"Matched" means the tubes are identical. Your amp (if it uses more than one power tube)
operates in "push-pull" the tubes seesaw back and forth, delivering their half every milisecond
or so. If the tubes are matched, these two signals will be the same level - and equal in power. Matching is not new. I find references to it as far back as amps were made (1930's and earlier) "NOS" is commonly used, it means New Old Stock. Tubes that were never sold (new) but in stock or stored for a long time. They are often Military tubes, stocked is some warehouse and forgotten "JAN" mean Joint Army Navy. Again, military tubes made to pretty exacting standards for WWII, Korean war and peacetime uses. They may also be considered NOS. "Bias" is the most confusing of all. To understand it you need to know (first) that the tubes we are using can do other things besides act as audio amplifiers. They can be switches, computer bytes, oscillators, voltage regulators etc. In order for them to amplify musical signals they have to operate at the correct voltage and be able to go up and down with the incoming signal. For this to work right the tubes, at rest, have to have a negative voltage at their "control grid" - the place the signal comes into the tube. This negative voltage is called bias and it needs to be adjusted for the type of tube in use, and since tubes vary somewhat, even within the same type, for the individual tubes used in the amplifier. Also for the "class" in which the operate. (this is the tricky Class A, class AB etc. stuff.) The real measurement of bias is how much current the tube uses, the negative voltage can be measured, but it is not as accurate as the current measurement Bias is not a "gimmick" and it has always existed. Some amps do not have adjustments - but could use them. Some amps don't even have a negative voltage supply, they use another trick called "cathode bias" to apply the negative voltage in a different manner. Torres Amps always have an adjustable bias, and/or a cathode bias. The more accurate the bias, the better the amp sounds. |
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| Preamp tube substitution SUPER INFO, very interesting"Amp Tips"
By Dan Torres "Clean up your act." (complete article available on our Literature page under "Vintage Guitar Reprints") This article will give you a few easy ways to make your tube amp cleaner sounding and/or modify the tone easily. Tube amplifiers can provide the absolute perfect clean tone for jazz, blues, Surf, rock, country, all kinds of music. It just takes some knowledge and the right approach. #1. Preamp tubes. It's pretty easy to clean up the amp and get a lot of very musical and unique tones by switching just a couple of tubes in the preamp. Normal guitar preamps use the 12AX7 (7025) tube as the main building block of the circuit. There are several other tubes that will plug into the socket with no circuit changes necessary. Each of them will change the gain and the tone of the preamp. Take a look at Chart #1 for some numbers, then a simplified explanation. Tube Gain 12AX7 = 100 5751 = 70 12AT7 = 60 12AZ7 = 60 6072/12AY7 = 44 5965/12AV7 = 27 12AU7/6189/5814 = 20 (Chart is used by permission of Torres Engineering Catalog #8) All of these tubes are "dual triodes," two circuits packaged in one tube. Therefore replacing a single 12AX7 with one of the alternates will change the gain of two stages of the preamp. To make it simple I will ignore the circuit losses and assume the maximum gain for each tube stage. With an input of .0001 volt two stages of a 12AX7 will boost the signal to 1 volt. But substitute a 6072 tube (available brand new now from the Torres Web Site) and the final gain is 0.1936. Only 19% of the gain of the 12AX7. This is much cleaner, less likely to distort. (Math .0001 X 100 X 100 again = 1 .0001 X 44 X 44 again - check out the chart = .1936) Application. Standard Fender two channel amps, like the Super Reverb, Twin Reverb, Deluxe Reverb, Vibroverb, Bandmaster etc. Change the second tube (V2) to a lower gain tube (this is the reverb/vibrato channel.) Stevie Ray Vaughan was very fond of the 5751 in his Super Reverbs for a cleaner tone. (Available brand new from the Torres Web Site.) Marshall JCM 800, JMP, Super Lead, Plexi, Fender Tweed amps like the Bassman, and Twin, try changing the second tube in these amps also. One channel Fender amps like the Princeton, change the first tube. See the "Tubes for your Amplifier" web page for all these tubes (the article continues with considerable technology and design explaination as "Clean Up Your Act" Vintage Guitar Reprint.) |
NOTICE - THE ORANGE DROP CAPACITORS USED IN OUR KITS HAVE BEEN 100% DISCONTINUED BY THE MANFACTURER FOR EVER. THEY WILL NEVER BE MADE IN THE U.S. AGAINHIGH QUALITY Mallory Tubular Capacitors will be included in your kitwe apolgize for this, but no one anywhere was warned or informed in any way prior to discontinuance.We can install any and all of our kits in our custom workshop - email for info.Check out Torres Guitars.com our new info site
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