Five Volt Fullwave Rectifier Tubes Mike@MDBVentures.com http://www.MDBVentures.com Tube# - Base - Fvolt - Famp - Vdrop - MaxPmA - MaxPv - notes 5AR4/GZ34-5DA - 5.0 - 1.9 - 17 - 250 - 450 - low Vdrop 5U4/5Y3 5AS4-A - 5T - 5.0 - 3.0 - 50 - 275 - 450 - improved 5U4 5AT4 - 5L - 5.0 - 5.5 - 30 - 800 - 550 - higher power 5U4 5AU4 - 5T - 5.0 - 3.75 - 50 - 325 - 400 - high power 5U4 5AW4 - 5T - 5.0 - 3.7 - 46 - 250 - 450 - long life 5U4 5AX4-GT - 5T - 5.0 - 2.5 - 65 - 175 - 350 - high power 5Y3 5AZ3 - 12BR - 5.0 - 3.0 - 44 - 275 - 600 - compactron 5U4 5AZ4 - 5T* - 5.0 - 2.0 - 60 - 125 - 350 - loctal 5Y3 5BC3 - 9QJ - 5.0 - 3.0 - 53 - 300 - 500 - compactron 5CG4 - 5L - 5.0 - 2.0 - ? - 125 - 400 5DJ4 - 8KS - 5.0 - 3.0 - 44 - 300 - 600 - redesigned 5U4 (higher volts) 5R4-G/GY- 5T - 5.0 - 2.0 - 67 - 250 - 750 - high voltage 5U4 5R4-GYA - 5T - 5.0 - 2.0 - 67 - 250 - 750 - high voltage 5U4 (ruggedized) 5R4-GYB - 5T - 5.0 - 2.0 - 63 - 250 - 900 - high voltage 5U4 (ruggedized) 5T4 - 5T - 5.0 - 2.0 - 45 - 225 - 450 - metal 5U4 5U4-G - 5T - 5.0 - 3.0 - 44 - 225 - 450 - octal 5Z3 5U4-GA - 5T - 5.0 - 3.0 - 44 - 250 - 450 5U4-GB - 5T - 5.0 - 3.0 - 50 - 275 - 450 5V3 - 5T - 5.0 - 3.8 - 47 - 350 - 425 - higher power 5U4 5V3-A - 5T - 5.0 - 3.0 - 42 - 415 - 550 - 5V3 reduced filament current 5V4-G/GA- 5L - 5.0 - 2.0 - 25 - 175 - 375 - octal 83-V 5W4-G/GT- 5T - 5.0 - 1.5 - 45 - 100 - 350 - low power 5Y3 5X4-G - 5Q - 5.0 - 3.0 - 58 - 225 - 450 - 5U4 diff pinout 5X4-GA - 5Q - 5.0 - 3.0 - 47 - 250 - 450 5Y3-G/GT- 5T - 5.0 - 2.0 - 60 - 125 - 350 - octal 80 5Y4-G/GT- 5Q - 5.0 - 2.0 - 60 - 125 - 350 - 5Y3 diff pinout 5Z3 - 5T - 5.0 - 3.0 - 58 - 225 - 450 - 4pin 5U4 5Z4 - 5L - 5.0 - 2.0 - 20 - 125 - 350 - low drop 5Y3 80 - 4C - 5.0 - 2.0 - 60 - 125 - 350 - 4pin 5Y3 83 - 4C - 5.0 - 3.0 - 15 - 225 - 450 - 4pin mercury vapour 83-V - 4C - 5.0 - 2.0 - 25 - 175 - 375 - 4pin 5V4 1641 - 8E - 5.0 - 3.0 - 44 - 250 - 450 - rabbit ear 5U4 5931 - 5T - 5.0 - 3.0 - 47 - 300 - 600 - industrial 5U4 6004 - 2AJ - 5.0 - 2.0 - 60 - 120 - 375 - rabbit ear 5Y3 6087 - 5L - 5.0 - 2.0 - 50 - 125 - 350 6106 - 5L - 5.0 - 2.0 - 60 - 125 - 350 6853 - 8HE - 5.0 - 1.7 - 60 - 125 - 350 RK60 - 8E - 5.0 - 3.0 - 44 - 250 - 450 - rabbit ear 5U4 Six Volt Fullwave Rectifier Tubes Tube# - Base - Fvolt - Famp - Vdrop - MaxPmA - MaxPv 6AX5-GT - 6S - 6.3 - 1.2 - 50 - 125 - 350 6AX6-G - 7Q - 6.3 - 2.5 - 21 - 250 - 350 6BW4 - 9DJ - 6.3 - 0.9 - 40 - 100 - 325 6BY5-G/GA-6CN - 6.3 - 1.6 - 32 - 175 - 375 6CA4 - 9M - 6.3 - 1.0 - ? - 150 - ? 6W5-G - 6S - 6.3 - 0.9 - 24 - 90 - 325 6X4 - 5BS - 6.3 - 0.6 - 22 - 90 - 360 6X5 - 6S - 6.3 - 0.6 - 22 - 80 - 360 6Z5 - 6K - 6.3 - 0.8* - ? - 60 - ? 6ZY5-G - 6S - 6.3 - 0.3 - 18 - 40 - 325 7Y4 - 5AB - 6.3 - 0.5 - 22 - 70 - 325 7Z4 - 5AB - 6.3 - 0.9 - 40 - 100 - 325 84/6Z4 - 4C - 6.3 - 0.3 - 20 - 60 - 325 5993 - 5993 - 6.3 - 0.8 - ? - 60 - 260 5852 - 6S - 6.3 - 1.2 - ? - 65 - 300 6202 - 5BS - 6.3 - 0.6 - 22 - 55 - 325 6203 - 9CD - 6.3 - 0.9 - 22 - 77 - 325 6325 - 6325 - 6.3 - 2.7 - ? - 250 - 780 6754 - 9ET - 6.3 - 1.0 - ? - 90 - 325 Misc Volt Fullwave Rectifier Tubes Tube# - Base - Fvolt - Famp - Vdrop - MaxPmA - MaxPv 0Z4 - 4R - none - none - ? - 110 - 880 82 - 4C - 2.5 - 3.0 - 15 - 115 - 450 3DG4 - 5DE - 3.3 - 3.8 - 32 - 400 - 325 12BW4 - 9DJ - 12.6 - 0.45 - 40 - 100 - 325 12DF5 - 9BS - 12.6 - 0.45 - 40 - 100 - 350 12X4 - 5BS - 12.6 - 0.3 - 22 - 90 - 360 25X6 - 7Q - 25.0 - 0.3 - 25 - 60 - 125 25Y5 - 6E - 25.0 - 0.3 - ? - 42 - 250 25Z5 - 6E - 25.0 - 0.3 - 22 - 75 - 235 25Z6 - 7Q - 25.0 - 0.3 - 22 - 75 - 235 26Z5 - 9BS - 26.5 - 0.2 - 22 - 50 - 325 28Z5 - 6BJ - 28.0 - 0.24 - 40 - 100 - 325 50AX6-G - 7Q - 50.0 - 0.3 - 21 - 250 - 350 50X6 - 7AJ - 50.0 - 0.15 - 22 - 75 - 235 50Y6 - 7Q - 50.0 - 0.15 - 22 - 75 - 235 50Y7 - 8AN - 50.0 - 0.15 - 22 - 75 - 235 50Z6 - 7B - 50.0 - 0.3 - ? - 75 - 235 50Z7 - 8AN - 50.0 - 0.15 - 21 - 65 - 235 117Z6 - 7Q - 117 - 0.075 - 15.5 - 60 - 235 5690 - 5690 - 12.6* - 1.2 - 17 - 125 - 350 5U4 Compatible Fullwave Rectifier Tubes Tube# - Base - Fvolt - Famp - Vdrop - MaxPmA - MaxPv - notes 5AR4/GZ34-5DA* - 5.0 - 1.9 - 17 - 250 - 450 - low Vdrop 5U4/5Y3 5AS4-A - 5T - 5.0 - 3.0 - 50 - 275 - 450 - improved 5U4 5AU4 - 5T - 5.0 - 3.75*- 50 - 325 - 400 - high power 5U4 5AW4 - 5T - 5.0 - 3.7* - 46 - 250 - 450 - long life 5U4 5DJ4 - 8KS* - 5.0 - 3.0 - 44 - 300 - 600 - redesigned 5U4 (higher volts) 5R4-G/GY- 5T - 5.0 - 2.0 - 67 - 250 - 750 - ruggedized 5U4 (higher volts) 5R4-GYA - 5T - 5.0 - 2.0 - 67 - 250 - 750 5R4-GYB - 5T - 5.0 - 2.0 - 63 - 250 - 900 5T4 - 5T - 5.0 - 2.0 - 45 - 225 - 450 - metal 5U4 5U4-G - 5T - 5.0 - 3.0 - 44 - 225 - 450 - octal 5Z3 5U4-GA - 5T - 5.0 - 3.0 - 44 - 250 - 450 5U4-GB - 5T - 5.0 - 3.0 - 50 - 275 - 450 5V3 - 5T - 5.0 - 3.8* - 47 - 350 - 425 - higher power 5U4 5V3-A - 5T - 5.0 - 3.0 - 42 - 415 - 550 - 5V3 reduced filament current 5931 - 5T - 5.0 - 3.0 - 47 - 300 - 600 - industrial 5U4 *Extra connections on base - may not be plug-in compatible in some circuits. *Higher heater current requirement - may not work in many 5U4 circuits. 5Y3 Compatible Fullwave Rectifier Tubes Tube# - Base - Fvolt - Famp - Vdrop - MaxPmA - MaxPv - notes 5AR4/GZ34-5DA* - 5.0 - 1.9 - 17 - 250 - 450 - low Vdrop 5U4/5Y3 5AX4-GT - 5T - 5.0 - 2.5* - 65 - 175 - 350 - high power 5Y3 5CG4 - 5L* - 5.0 - 2.0 - ? - 125 - 400 5R4-G/GY- 5T - 5.0 - 2.0 - 67 - 250 - 750 - ruggedized 5U4 (higher volts) 5R4-GYA - 5T - 5.0 - 2.0 - 67 - 250 - 750 5R4-GYB - 5T - 5.0 - 2.0 - 63 - 250 - 900 5T4 - 5T - 5.0 - 2.0 - 45 - 225 - 450 - metal 5U4 5V4-G/GA- 5L* - 5.0 - 2.0 - 25 - 175 - 375 - octal 83-V 5W4-G/GT- 5T - 5.0 - 1.5 - 45 - 100 - 350 - low power 5Y3 5Y3-G/GT- 5T - 5.0 - 2.0 - 60 - 125 - 350 - octal 80 5Z4 - 5L* - 5.0 - 2.0 - 20 - 125 - 350 - low drop 5Y3 6087 - 5L* - 5.0 - 2.0 - 50 - 125 - 350 - special 5Y3 6106 - 5L* - 5.0 - 2.0 - 60 - 125 - 350 - special 5Y3 6853 - 8HE* - 5.0 - 1.7 - 60 - 125 - 350 *Extra connections on base - may not be plug-in compatible in some circuits. *Higher heater current requirement - may not work in many 5Y3 circuits. Four Pin Fullwave Rectifier Tubes Tube# - Base - Fvolt - Famp - Vdrop - MaxPmA - MaxPv - notes 5Z3 - 4C - 5.0 - 3.0 - 58 - 225 - 450 - 4pin 5U4 80 - 4C - 5.0 - 2.0 - 60 - 125 - 350 - 4pin 5Y3 83 - 4C - 5.0 - 3.0 - 15 - 225 - 450 - 4pin mercury vapour 83-V - 4C - 5.0 - 2.0 - 25 - 175 - 375 - 4pin 5V4 Why use a different rectifier tube? Normally the best replacement tube is to use the same type tube number as originally designed for the circuit. These days it is sometimes the case that the original tube is not available, hard to find, or very expensive. Many times substitutions can be used that may be more readily available, or lower cost, yet still perform in the circuit as well as the originally designated tube type. There are two basic fullwave power rectifier tubes that you will likely encounter. The 5Y3 family, and the 5U4 family. The 5Y3 family is the oldest fullwave rectifier design. The 5Y3 design goes all the way back to the 1920s (type 80 tube) and is still being made today. The original design was the type 80 tube. When the octal base format came into use, the type 80 tube had an octal base put on it and the type became the 5Y3. You can swap between the tubes using a base adapter. The orignal type 80 tube came in a globe/balloon style. Later the type 80 was switched to the ST shape which is more rugged because it supports the internal elements. Long after the end of design life for the type 80 tube, it was made available in the GT style for replacement use. This was really just a 5Y3GT with a four pin base. When the 5Y3 came out, all they did was to put an octal base on the type 80 tube. At this time, the type 80 tubes were using the ST shaped glass, so the first 5Y3 tubes, which were called 5Y3G, also used the ST shape. Later on as equipment manufacturers demanded smaller tubes, the 5Y3 was packed into the smaller GT style. Beyond that, the design remains largely the same as when the type 80 tube was first introduced. Origonally if more power than the type 80 tube could provide was needed, you needed to design in two or more tubes. The main reason for requiring two tubes was that the heat disipation for a fullwave rectifier of that power would be too much to handle in the standard size tube. To deal with this, the type 83 tube was designed. The type 83 tube uses mercury vapour (the same gas in florescent lights) to reduce the internal resistance. Doing so reduces the amount of power disipated by the tube and thus the heat generated. This allows a high power fullwave rectifier to be placed in the same package as the original type 80 tube. The down side to this is that the mercury creates its own set of problems. The toxic aspects of mercury were not considered to be as big an issue at that time as it is now. However there are other problems. The primary problem is that mercury is a liquid at room temperature. That causes it to condense onto the internal tube elements. If voltage is applied to the plates before the heater has warmed up the tube (and turn the mercury into gas), the mercury can cause internal shorting or arcing to occur. This can cause damage to the tube and to the circuits in which it is used. Note: there is a tube type called 83-V. It is unfortunate that they selected the "83" number for it as it is rather different than a type 83 tube. It is closer to a type 80 tube but with a reduced internal resistance. The reduced resistance is achieved by placing the cathode/heater and plate closer together. This makes it much harder to manufacture and more suceptable to shorting out. A shorted power rectifier tube can cause a lot of damage to the circuits in which it is used. There were various attempts made to deal with the mercury problem in the type 83 tube. One solution was the 5Z3 tube. The 5Z3 tube uses a larger glass bulb and larger plates to handle the higher power. It also has a bigger heater so that it can emit more electrons that are required for the higher power levels. The end result is a tube with twice the plate current as a type 80 or 5Y3 tube and slightly more plate voltage. For high power amplifiers, radios and TVs, this was just what was needed. The 5Z3 uses the same base and pin out as the type 80 tube, so it is actually possible to put a 5Z3 in a type 80 socket. Normally this should be avoided though, the 5Z3 uses a 3amp heater whereas a type 80 tube uses a 2amp heater. Putting a 5Z3 in a type 80 circuit will likely cause the power transformer to overheat and fail. Conversely, putting a type 80 tube in a 5Z3 circuit will likely overdrive the tyep 80 tube causing it to fail very quickly. Like the type 80, when the octal socket came into use, the 5Z3 had an octal base put on it and it became the 5U4. The "G" style 5U4 is the original 5Z3 ST shaped tube using an octal base. Also like the 5Y3, the tube was reduced in size by using a GT bulb. The 5U4GT bulb is much larger than the 5Y3GT bulb to accommodate the larger 5U4 plates. There are two basic 5U4GT tubes. The 5U4GA and the 5U4GB. The GA is simply the old 5U4G crammed into a smaller GT bulb. The GB is a GA with an improved design (slightly more power output). Originally the 5U4GB design was called the 5AS4 (ST version) and later the 5AS4A (GT version). Due to lack of sales and multiple inventory issues for a tube that was essentially the same as the 5U4, manufacturers decided to name it the 5U4GB and retire the 5U4, 5U4GA and 5AS4 tubes. You will often see tubes labeled 5U4GA/GB or 5U4GB/5AS4A indicating that they are intended for replacement of those tube types. For new designs the differences are not normally a problem, and for most radio and TV designs the differences are minor enough to not make a difference. For some audio amplifiers the slight differences in design can result in a shift of voltages enough to make a noticable difference in the way the amplifier sounds. In a properly designed amplifier the different tubes should not cause damage to the amplifier. Switching between the various types can be a way to tweak the amplifier for a different sound. The general rule of thumb is that a tube with more voltage drop will make the amplifier sound more mellow and one with less voltage drop will sound more firm. However the nature of the beast is that the actual results will depend heavily on the amplifier design and the other tubes used in the amplifier. Another aspect is that a used tube can make a difference in the sound of an amplifier. As a tube ages, the number of electrons emited from the cathode is reduced. This has the effect of increasing the voltage drop across the tube. The result is that an old amplifer with well used tubes can sound more mellow than a new amplifier of the same design. Over the years other tubes have been designed that take their history from the original type 80 and type 5Z3 tubes. Some were designed to have lower voltage drop, others to have more or less maximum plate current and or plate voltage. One of the more popular replacement versions is the 5T4 which is a metal version of the 5U4/5Y3 tube. Because it uses a 2 amp heater but has the voltage and current rating of a 5U4, the 5T4 can be used in place of either a 5U4 or a 5Y3 in most circuits. The 5T4 tube is no longer made, but there are still a lot of them available as the military used them extensively. Because of the metal envelope, the tube is very rugged. The main problem is that since it is metal, you cannot see inside the tube to see if it is gassy, arcing or the heater is not working. Also it is taller (the same bottle as the metal 6L6) than the 5Y3, so it may not physically fit in circuits using the 5Y3. Another popular replacement version with a 2amp heater that allows it to be used in either 5U4 or 5Y3 circuits is the 5R4 tube. The 5R4 also has a significantly higher plate voltage and a low loss base. The GYA and GYB versions are highly ruggedized for aircraft use. The main problem is that the higher plate voltage also means a higher voltage drop across the tube. Also the GYA and GYB verisons have large heavy bases as a part of the ruggedization. A popular tube still being made is the 5AR4/GZ34. This is basically an improved redesigned 5U4/5Y3 tube. It has a 1.9amp heater and plate voltage and current similar to the 5U4 so it can be used in either circuit. However it has a much lower voltage drop so care should be used to be sure that the circuit can handle the extra current surge. This tube is usually best used in a circuit that is designed to handle the low voltage drop. The other potential problem with this tube is that it has an internal connection on pin 1 which can potentially cause problems with some circuits. Don't use this tube unless you know that the circuit can handle it. Another popular redesigned tube that is still in production is the 5DJ4. This tube is essentially a 5U4 with higher plate voltage and current. It also has extra connections on the base which can be a potential problem. Like the 5AR4, don't use this tube unless you know that the circuit can handle it. Serious damage can potentially occur in some circuits. If you need the higher voltage or current of the 5DJ4 but the extra connections on the base are a problem, consider the 5831. The 5831 has similar characteristics but with the standard 5U4 pinout. Generally you should stay away from the 5AU4 or 5AW4 tubes as replacements for a 5U4. These tubes have 20% higher filament current which can cause the power transformer to overheat if it is not designed to take the extra load. If you know that the transformer can handle the extra current, then you can use them. The 5AU4 is designed to have more current output and the 5AW4 is designed to have a longer life. Unless you have a specific need for one of these tubes, you should consider one of the other tubes as a substitute. Neither of these tubes is being made anymore. The 5V3 is another one of the troublesome tube numbers. There are two versions of the tube, the 5V3 and the 5V3A. The 5V3 should be avoided as a 5U4 replacement because it has a 20% higher heater current which can potentially damage the power transformer. The 5V3A has the same heater current as the 5U4 and can be safely used as a substitute. The main advantage of the 5V3 is that it has a higher plate current and voltage. so it can be used in more demanding circuits (or last longer in undemanding circuits). However given the serious difference between the 5V3 and 5V3A types, extreme care must be used that you don't accidently put the wrong tube in a circuit that cannot handle it. For circuits that use a 5Y3, there are a few more options available for substitution. For low voltage drop, as well as the 5AR4, there are the 5V4 and 5Z4 tubes. The 5V4 tube comes in the older ST style "G" glass and in the newer "GT" style glass. The 5V4 is an octal version of the four pin 83-V tube. The 5Z4 also comes in the ST and GT styles, but has slightly lower voltage drop (20v vs 25v). These tubes don't have quite as much plate voltage as the 5AR4, but will work in a circuit designed for the 5Y3 as long as the lower voltage drop is not a problem. The 5CG4 is rare, but is essentially a 5V4 type tube in a small GT package. The 5W4 tube is a lower power version of the 5Y3. It uses less power so it runs cooler and lasts longer, but it may not work in all circuits due to the lower plate current rating. There are also three special industrial/military versions of the 5Y3. The 6087 is the same as the 5Y3 but is in a low loss base and rugged construction for mobile and aircraft use. The 6106 is a highly specialized version of the 5Y3 tube. It is a Bendix Red Bank tube. These tubes where designed for the military to withstand the most punishment that could be thrown at a tube. These are the best 5Y3 tubes ever made. The 6853 is an industrial version of the 5Y3. It has a lower filament current so that it lasts longer. The rest of the characteristics are the same as a normal 5Y3. How to decide if you can use a different tube type. The commonly used replacement tubes for the 5U4 and 5Y3 tubes are listed in the 5U4/5Y3 Compatible Fullwave Rectifier Tubes tables above. The first thing to check is the filament voltage and current. The replacement tube should have the same filament voltage. The filament current should be equal to or less than the original design. Lower filament current usually means the tube is not able to handle the same power levels as the original design, but not always. The plate characteristics need to be checked to see if it will work. Higher filament currents should be avoided as they can cause the power transformer to overheat and fail unless it is designed to handle the higher current requirement. Note: If the rectifier tube is used in a series strung heater circuit, then the voltage and current ratings for the tube must be exactly the same as the original tube. Generally for those types of circuits it is best to stay with the original tube number. Normally you won't encounter a series strung heater circuit unless it is a radio or TV. Radios commonly used series strung heaters to reduce cost by eliminating the power transformer. Some very low cost TVs did the same thing. Normally though series strung radios used halfwave rectifier tubes specifically designed for radio work and TVs that used series strung heaters used solid state rectifiers instead. Generally, if the rectfier is a 5U4 or 5Y3 tube, it is unlikely that the circuit it series strung as the tube normally requires a power transformer with a separate filament winding for the tube. The next thing to check is the maximum plate voltage. The maximum plate voltage should be at least as high as the tube you are replacing. If you know the maximum voltage that will be encountered is less than the tube rating, you may be able to use a lower rated tube, but care must be used as an underrated tube may arc internally causing potential circuit damage if the plate voltage rating is exceeded. Next you will want to check the maximum plate current capability. Like the plate voltage rating, the maximum plate current rating should be equal to or greater than the tube being replaced. With plate current there is greater flexability as often the maximum rating of the tube is seldom reached. You may be able to get away with a lower rated tube. The problem that can be encountered here is the tube may be over driven causing shorter life for the tube and possible power supply collapse. Usually this isn't as damaging as when the tube experiences internal arcing, but in some circuits it may potentially be a problem. If you are not sure, always go with equal to or better current rating for the plates. Finally, look at the tube voltage drop. This is normally a characteristic that is not as much a problem. In radios and TVs it often has little or no impact as they are typically designed to handle the varience. In amplifiers, it can affect how the amplifier sounds. Especially amplifiers that use fixed bias and little or no inverse feedback. When considering the voltage drop, keep in mind that the rated voltage drop is normally given for the maximum voltage and current rating for the plate. The actual voltage drop in use will depend on the current flow through the plate and the voltage applied. The voltage drop for a given voltage and current will also depend on the construction of the tube. Some tubes will have a higher variablity of the voltage drop as the current changes and others will have less of a change. Generally a tube with a lower voltage drop design will have less of a change in the voltage drop with a change in the plate current. A well used tube will generally exhibit a larger change in voltage drop with a change in the plate current. One of the characteristics of a gas rectifier (such as a mercury rectifier) is that they tend to exhibit less of a change in the voltage drop. Mercury vapour tubes are very stable in this regard (which is the primary reason that Hickok used the type 83 tube in their tube tester). Neon, Xeon, and Argon are other gases that are popular to use in gas rectifiers. The purpose of the gas is to provide a plasma inside the tube which reduces the internal resistance during operation. This characteristic comes with a price though. The gas will not ionize (turn into plasma) until a relatively high voltage is developed across the tube. This is typically between 50 volts and 150 volts. The exact voltage at which the ionization starts is dependant upon a number of factors, including temperature of the tube, the type and amount of gas used, and the internal construction of the tube (distance between the plate and cathode). Once the ionization occurs the tube resistance drops rapidly (within microseconds). This causes a strong current surge which can disrupt or harm the circuits if they are not designed to handle this situation. This can be especially harmful to high value electrolytic capacitors as the rapid incease in voltage can cause a high current surge into the capacitor as the circuit tries to charge up the capacitor. This can cause the capacitor to overheat which can result in it venting some of all of its electrolyte. This damages the capacitor. Usually resulting in the capacitance being reduced, or in extreme cases the capacitor will explode. It is best to have inductive or resitive loading in the recitfier circuit when using a gas rectifier to protect the capacitor from being damaged by the current surge. Solid State Fullwave Rectifier Tube Replacements An alternative to using a vacuum tube replacement is to use a solid state tube replacement. Most of the replacements available use a pair of silicon diodes to replace the vacuum tube rectifier elements. The silicon rectifier has several big advantages. One is that they will normally last for the life of the device they are used in. Also since they don't require a heater to boil electrons off the cathode material, they use far less power and don't generate the heat like vacuum tube rectifiers. They do have one disadvantage though, they have very little internal resistance. This can potentially cause trouble in some vacuum tube circuits. The low resistance can cause higher surge currents in the rectifier circuit which can shorten the life of electrolytic capacitors. it can also cause an increase in hum bleed-thru since the internal resistance of the vacuum tube rectifier is normally included as a part of the power supply filtering in a tube circuit. Some solid state tube rectifier replacements account for this by including a resistor in the circuit to emulate the internal resistance of the original tube. However the resistor is an added source of heat and makes the replacement more expensive to make, so most do not include the resistor. If the circuit can handle the solid state rectifier, it can provide more power because of the reduced power loss compared to a vaccum tube. If you can handle a soldering iron, it is easy to make a solid state 5Y3 or 5U4 tube replacement. First get an octal plug. This can be bought from a tube supplier, or can be obtained by removing one from a dead tube. Next you will need two 1N4007 diodes. These are available from most electronics suppliers. Just about any diode with a current rating of at least one amp and a voltage of 1000V or higher will work. Note: Diodes require higher ratings than tubes because they are not as forgiving as tubes. A tube can normally withstand a momentary event that exceeds it's rating without permanent damage. Solid state diodes cannot, they will fail immediately. Because of that, the diode rating needs to be selected such that it will never be possible for it to be exceeded. The general rule of thumb is to use at least double the voltage and current rating as the design calls for. To construct the rectifier tube replacement, connect the anode of one diode to pin 4 and the cathode to pin 8. Connect the anode of the other diode to pin 6 and the cathode also to pin 8. For a four pin rectifier, connect one diode anode to pin 2 and the other diode anode to pin 3. Connect the cathodes of the diodes to pin 4. Congradulations, you now have a solid state tube replacement. However, you aren't done yet. As was noted above, solid state rectifier tube replacements have much lower internal resistance compared to vacuum tube rectifiers. This can cause problems and potentially even damage to the circuits if they are not designed to handle this difference. There are two ways to fix this. One is to modify the circuit by placing a resistor in series with the plate supply transformer center tap and ground. The other way you can fix this is by adding the resistor in series with the cathodes of the diodes and pin 8 (pin 4 on 4pin tubes). The advantage of placing the resistor in the solid state rectifier tube replacement is that you are not modifying the circuit so that you can easily plug a regular vacuum tube in the circuit again without removing the added resistor from the circuit. The disadvantage of placing the resistor in the solid state rectifier tube replacement is that the resistor will get hot and will have dangerous voltages on it. It is strongly recommended that you properly insulate the solid state rectifier tube replacement so that you do not accidently touch the exposed lethal voltages on the connections. Design note: The recommended design for 5U4 and 5Y3 tubes is to take power off pin 8 of the filament. A few designs take the power from pin 2. This may result in increased hum because of the filament voltage getting into the DC power. To fix this, you can either rewire the circuit to take power from pin 8, or move the cathodes of the diodes in the solid state tube replacement to pin 2. Do not short pins 2 and 8 as this will short out the heater supply and damage the circuits. For the four pin rectifiers, the wiring is even less consistent than with the octal circuits. You may need to move the cathodes to pin 1 instead of pin 4. As with the octal tube replacement, do not short pins 1 and 4 or you will damage the circuits. While in some cases you may be able to get away without using the resistor, in others it may be wise to use it to prevent damage to the circuits or change in the characteristics of the circuit. The chart below provides some suggested values to use. As with all things like this, these are only suggested values. The actual ideal values will be specific to the circuit and use. Selecting the resistor for the solid state rectifier tube replacement. 5AR4 - 20 ohms 10 watts 5AS4 - 20 ohms 10 watts 5AU4 - 30 ohms 10 watts 5AW4 - 150 ohms 10 watts 5AX4 - 47 ohms 2 watts 5DJ4 - 100 ohms 10 watts 5T4 - 150 ohms 10 watts 5U4G/GA - 150 ohms 10 watts 5U4GB - 20 ohms 10 watts 5V4(all) - 100 ohms 5 watts 5W4(all) - 47 ohms 2 watts 5Y3(all) - 47 ohms 2 watts 5Z4 - 47 ohms 2 watts 80 - 47 ohms 2 watts 83 - 10 ohms 2 watts 83V - 47 ohms 2 watts 5Z3 - 150 ohms 10 watts Note: replacement of the 5R4 with a solid state tube replacement is not recommended without careful review of the circuit in which it is used. If the 5R4 is being used in a circuit where the 5U4 would normally be installed, use the 5U4 resistor. Note: Silicon rectifier diodes have a typical voltage drop of between 0.5volt and 1.0volt. This can be averaged to 0.75volts for the math. Divide this by the current flow to get the effective resistance. Thus for a 250mA tube circuit you would get 0.75 / 0.25 = 3 ohms. This is much lower than the 44 ohms of a normal 5U4 tube. Another way to determine the resistor is to install a new tube in the circuit and set it up to use the maximum amount of power it would normally use. Measure the voltage between ground and the power take-off pin (typically pin 8 for octal, pin 4 for 4pin types). Mark this voltage down as a reference. Note: these voltages don't have to be super accurate. A 5% tolerance for this type of work is more than adequate. Most tube circuits are designed to handle tolerances of 10% to 20% or even more. Remove the rectifier tube and install the solid state tube replacement using a variable resistor with the appropriate wattage for the resistor. Set the resistor value to the value listed in the table. Again apply power and set up the circuit for the maximum normal load. While measuring the power takeoff voltage, adjust the resistor to achieve the same voltage as obtained with the new tube. Turn off the power, remove the variable resistor from the circuit and measure the resistance of the variable resistor for that obtained setting (be sure not to disturb the setting). This is the value of resistor that should be used with the circuit. (You can use the next closest standard resistance value available.) The wattage is determined by multiplying the square of the maximum current in amps times the resistance. Then use the next higher wattage resistor. Thus for a 5U4 circuit rated at 225mA using a 150 ohm resistor; 0.225*0.225*150=7.6watts. For this you would use a 10watt resistor. Generally try to pick a wattage 20% to 50% higher to prevent the resistor from overheating and burning up. Do not use a resistor with less wattage or it will overheat. Do not use a resistor with too high of a wattage either. A part of the purpose of the resistor is to act as a safety valve in case the diodes short out. The resistor should burn out before the shorted diode destroys the rest of the circuits. Always be sure to provide adequate ventalation for power resistors so that the heat can escape. Also keep them away from other parts that can be damaged by the heat. Unfortunately, where the normal failure for a tube is to fail open, the normal failure for a solid state diode is to short out. This can potentially cause nasty damage to the circuits. Warning: Use extreme caution when working with tube circuits. Do not do this work if you are not qualified to do it. The voltages in tube circuits are lethal and can kill you.