a tube primer for guitar and bass players - Guitar Amplifier Blueprinting

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This is a THD Univalve. This is a single ended class A amplifier that one can change the tubes in with no adjustment necessary. There are a lot of other features on this amp. This amp is a great tool in the studio or for smaller club live work. Some folks think of amps such as Vox AX-30 amps as class A amps. Although this is somewhat accurate, they are really cathode biased push-pull amps. The Univalve is a true class A amp with no feedback loop. The THD UV is a MUST for any studio. For more information go to www.thdelectronics.com Two Doctor Z amps, perhaps on each end of his product line. The red one is a Carmen Ghia, one of the coolest amps around and a great studio and recording amp. The tan amp is a KT-45 with loads of clean headroom, but with it’s tone controls pushing a pentode front end (an EF-86, this amp is capable of a lot of gain too. The pair of these amps will cover just about any music base. Dr. Z has a LOT more amps, all of original design, and all built hand wired to extremely high standards. For more see www.drzamps.com 16
Preamp Tubes Please note that the tests on tubes were done on raw factory samples. Some tube vendors test and/or select or grade, and some do not. Many rely on the end user’s reluctance to return a single tube such as a preamp tube for problems, so just send their tubes out with no testing or minimal testing. A preamp tube that is not microphonic when first installed, can become microphonic in short order after a few heat up and cool down cycles with expansion and contraction. This is one reason to know and trust your vendor. Some companies such as Groove Tubes have a very long warranty on tubes, in the case of preamp tubes, six months. Some reasons for the cost of GT premium tubes are due to the labor intensive testing process (each tube, one at a time, in place in high gain amps and tested for various attributes), and their cost for the tubes initially when buying from the major tube factories. In many cases, the GT reject rate is in excess of 60%. The data below, are for the raw factory samples, not GT tested examples. This is the way they come from the factory, and the sort of performance you can expect if your vendor does not test for gain, output, noise and microphonics. In the case of power tubes, gas leakage, grid leakage, and low vacuum are also test parameters that require expensive and complex test equipment which very few vendors have in house. The complete list of Groove Tubes preamp tubes can be seen at: http://www.groovetubes.com/tubes_list.cfm?ObjectGroup_ID=107 SAG – Special Applications Group (specifically selected tubes for specific needs) As you will learn throughout this document, all tubes, new or NOS are subject to very wide variations in characteristics. As an example, a 12AX7 is supposed to have as spec, a gain of 100, a transconductance of 1600 and a current output of 1.2 milliamps at a reference test voltage and bias. Tubes will typically vary +/- 50% or more, even ones tested from most vendors. For GT preamp tubes, this spread is much narrower, as the testing acceptance margins are tighter. Still, you do not know what you are actually getting in any case. One problem that kept coming into play, was a player would decide to retube the preamp section of his or her amp. The amp sounded worse in some cases with the new tubes. It was noted that perhaps the old tube had a current output of 1.0 milliamps, while the new tube only had a current output of 0.7 milliamps. This was a 30% drop in actual power off the first gain stage. Searching through tubes until one was found that met or exceeded the specs of the original tube would solve the problem and bring the amp back to life. It was found that things could be made even better, actually moving up or down in various tube characteristic parameters, to dial in to a particular player’s taste of needs. Tubes with more or less gain, more or less current, faster or slower rise time (more or less compression), and other factors were “tweeked” as the player went from one tube to another. This is one of the cornerstones of amplifier blueprinting. Matched phase inverters also came to pass in this process, there is more on this later. 17
Page 1 and 2: A TUBE PRIMER FOR GUITAR AND BASS P
Page 3 and 4: 6V6 OUTPUT TUBES ..................
Page 5 and 6: DITTO - The Swiss Army Knife of the
Page 7 and 8: THE ‘MARSHALL” STYLE AMPS in th
Page 9 and 10: HUGE ROCK AMP COMBO FOR THE CLASSIC
Page 11 and 12: Great designs with something worth
Page 13 and 14: Biasing in brief Bias your amp prop
Page 15: The Dr. Z Carmen Ghia. Sure, the go
Page 19 and 20: The basics of preamp tube differenc
Page 21 and 22: 12AX7 (ECC83, 7025, 12AT7, 12AY7, 1
Page 23 and 24: Keep in mind, the specs on the tube
Page 25 and 26: 12AX7-R2 - Sovtek 12AX7LPS Gain: 83
Page 27 and 28: ECC83-S - from the JJ factory Gain:
Page 29 and 30: 5751 New Manufacture Expected Gain
Page 31 and 32: The famed 7199 gold pin of the past
Page 33 and 34: 12AX7R3 Electro Harmonix (10/29/02)
Page 35 and 36: Additional Small Signal Tube Tests
Page 37 and 38: Recent tube test results DATE TUBE
Page 39 and 40: Fairly wide current spread, so bewa
Page 41 and 42: DATE TUBE B+ BIAS mA TC (gm) gp Gai
Page 43 and 44: B+ BIAS mA TC (gm) TUBE volts volts
Page 45 and 46: B+ BIAS mA TC (gm) DATE TUBE volts
Page 47 and 48: This is simply a basic power output
Page 49 and 50: Maximum plate dissipation on tubes
Page 51 and 52: 6V6C - a new 6V6 off new tooling th
Page 53 and 54: This is the 6L6C or straight bottle
Page 55 and 56: 6L6-R2 - The Svetlana 6L6. Prior to
Page 57 and 58: KT-66-HP - Russia, built under cont
Page 59 and 60: EL34 - E34LS - and 6CA7 types 59
Page 61 and 62: EL34C - Chinese EL-34 (25 watt tube
Page 63 and 64: The Groove Tubes GT-6CA7GE “The G
Page 65 and 66: The RCA Gray Plate. 65
Page 67 and 68:
Power output comparison test result
Page 69 and 70:
RCA 7027A NOS A big KT-90 69
Page 71 and 72:
The KT-88C A very strong KT88, with
Page 73 and 74:
Sorry, but I just HAD to show a pho
Page 75 and 76:
6550-R - Russian 6550, takes longer
Page 77 and 78:
Power comparison chart of current o
Page 80 and 81:
A pair of the famed Telefunken NOS
Page 82 and 83:
Output power chart for EL-84 family
Page 84 and 85:
New Electro Harmonix EL-84 (June 20
Page 86 and 87:
These are some of the 1980s JAN Phi
Page 88 and 89:
The 5R4-GYB, often used in place of
Page 90 and 91:
5U4GB above - 362 volts max. 5V4G a
Page 92 and 93:
The GT Rating system - an explanati
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a tube primer for guitar and bass players - Guitar Amplifier Blueprinting

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