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Some Thoughts by Jerry Byrd - Another gem from da chief on steel guitar fads and gimmicks
The Queen's Songbook - a new collection of famous and previously unpublished songs written by Lili`uokalani. Jerry Byrd's Instruction Course - where to order this steel guitar classic "So You Want to Play Hawaiian Steel Guitar" - a lesson from Alan Akaka
Tunings for Steel Guitar - by John Ely
Tech Tips - Build a Steel! - John Tipka on steel guitar building.
'Da Book' - Lorene's great new sourcebook ©2000 by Ely Music/Pub |
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From the Winter 2000 Quarterly Vacuum Tube Life and the Standby SwitchBy John W. Tipka Some members whom I have met at our conventions have asked me to continue writing articles covering various facets of the steel guitar and amplifiers. This is one of those articles. It pertains only to those amplifiers using vacuum tubes AND a standby switch. I have seen what I call "amplifier abuse" on many occasions on the part of many guitar players using high-power vacuum tube amplifiers. They plug in their guitar, turn on their amplifier, and start playing without regard to what is happening inside of the amplifier. If it is a low-output power amplifier (10 or 12 watts) that is probably all that you have to do because of the design. But if it is a higher-powered amplifier such as a Fender Twin Reverb, Deluxe Reverb, Vibrasonic, Bassman, or Marshall, in many cases it is using voltages that exceed the vacuum tube manufacturer's ratings, and precautions need to be taken to ensure long tube life. Most, if not all, of these amplifiers have a STANDBY switch to control the application of high voltage to the tubes. If you have a STANDBY switch on your amplifier, you might ask, "Why is it there and how do I use it?" The standby switch is used to turn off the high voltage to the amplifier's tubes. The high voltage causes current to flow in the vacuum tubes. Current flow is the movement of negatively charged electrons to a more positive place. The vacuum tube emits the electrons from a cathode and they are collected by a more positive anode or plate contained within the vacuum. If a voltage more positive than the cathode is not present on the anode, the negatively charged electrons emitted from a heated cathode will not be attracted to the anode and, therefore, there is no current flow and no amplification. A small voltage less positive than the operating voltage on the anode is used to heat the cathode. Amplifier startup begins with the application of this (filament) voltage to the tube cathodes (filaments) to bring them up to the temperature needed to drive off electrons. In most cases, it takes from 45 to 60 seconds to reach the proper operating temperature for the cathode. It is during this warm-up time that damage to the vacuum tubes occurs when the high voltage is applied and it peaks simultaneously. This is the time when the STANDBY switch should be OFF (open), preventing current flow and damage to the vacuum tubes. How are the tubes being damaged? If voltage is applied to the tubes before the cathode is hot and is freely emitting electrons, the HIGH VOLTAGE on the plate is essentially tearing electrons from the cathode material (thoriated tungsten). Generally, this is called cathode stripping. When most of the electron emitting material is eventually depleted or stripped from the cathode, the tube is ruined and can no longer deliver enough electrons to operate as designed. In this case, the tube must be replaced prematurely to restore the amplifier to its original design specifications. It is for this reason that, when first turning on your amplifier, it is very important to take the plate voltage off of the tubes by placing the STANDBY switch in the OFF position for a least one minute. This process can be watered down somewhat in amplifiers that use the full wave rectifier tube types 5V4 or 5AR4/GZ34. These tubes use an indirectly heated cathode which means that, as the cathode comes up to temperature and starts emitting electrons, the rectified voltage does not peak immediately upon "turn on." The slower, controlled rise in the high voltage does not strip the cathodes warming gradually as readily as with voltage at its full potential on cold or unheated cathodes. Use of the STANDBY switch may not be as important in these cases but would still be a good practice to follow, regardless. My advice for long tube life in amplifiers with a STANDBY switch: When first turning on the amplifier, 1. Place the STANDBY switch in the OFF position. 2. Switch the POWER switch ON. 3. Wait at least one minute before moving the STANDBY switch to the ON position. Turn off the amplifier with the POWER switch leaving the STANDBY switch in the ON position. This bleeds the high voltage within the amplifier. With the next start up, repeat the procedure described above. 
HSGA * HAWAIIAN
STEEL GUITAR ASSOCIATION Homepage URL: www.hsga.org (hsga@lava.net) Last updated: 07/23/02 by Gerald Ross (gbross@umich.edu) |
