Tripple Triode Substitutions 29 May 2011 - revised 26 April 2017 Mike at MDBVentures.com Visit us at http://www.MDBVentures.com - Great prices on great tubes! With the shortage of 6C10 and 6K11 Compactron triodes, many people have been attempting to substitute other triodes that are still available. Unfortuantley, the substitutions seldom work. There are 13 Compactron triodes that are interchangable physically, but their characteristics are quite different as shown below. * These tubes have an internal shield -------------------------------------------------------------------------------------------------------------- Tube : Heater Plate Watts Max Plate V Max Plate mA Gain M. Conductance Plate Resistance 6AC10 : 6.3V 0.6A 2/2/2W 330/330/330V 9/9/9mA 62/62/62x 5800/5800/5800Gm 10700/10700/10700rp 6AK10 : 6.3V 0.9A 2/2/2W 330/330/330V 10/10/10mA 53/53/53x 7000/7000/7000Gm 7500/7500/7500rp 6AV11 :* 6.3V 0.6A 2/2/2W 330/330/330V 10.5/10.5/10.5mA 17/17/17x 2200/2200/2200Gm 7700/7700/7700rp 6BK11 :* 6.3V 0.6A 0.4/0.4/0.4W 330/330/330V 1.6/1.2/1.2mA 70/100/100x 1550/1600/1600Gm 45000/62500/62500rp 6C10 :* 6.3V 0.6A 1/1/1W 330/330/330V 1.2/1.2/1.2mA 100/100/100x 1600/1600/1600Gm 62500/62500/62500rp 6D10 :* 6.3V 0.45A 2/2/2W 330/330/330V 4.2/4.2/4.2mA 57/57/57x 4200/4200/4200Gm 13600/13600/13600rp 6K11 :* 6.3V 0.6A 0.275/0.3/0.3W 330/330/330V 10.5/1.2/1.2mA 17/100/100x 2200/1600/1600Gm 7700/62500/62500rp 6Q11 :* 6.3V 0.6A 3/1.2/1.2W 330/330/330V 22/22/1.2mA 18/100/100x 2500/1600/1600Gm 7000/62500/62500rp 6U10 : 6.3V 0.6A 2/2/1W 330/330/330V 9.6/9.6/1.2mA 18/18/100x 2300/2300/1600Gm 7700/7700/61000rp 9AM10 : 9.5V 0.6A 2/2/2W 100/100/100V 8/8/8mA 64/64/64x 6900/6900/6900Gm 9300/9300/9300rp -------------------------------------------------------------------------------------------------------------- Tube : Heater Other specs 8AC10 : 8.4V 0.45A --- same as 6AC10 --- 12AC10 : 12.6V 0.3A --- same as 6AC10 --- 9AK10 : 9.5V 0.6A --- same as 6AK10 --- Possible substitutions (those marked with * may not work) 6AC10 <-> 6AK10*, 6D10*, 8AC10*, 9AM10* 6C10 <-> 6AC10*, 6BK11* 6K11 <-> 6Q11 Alternatives: There are three special industrial grade tripple triodes that are similar to the regular Compactron tripple triodes However, they have different pinouts, so they are not drop in replacements. They might work with the socket being rewired or with the use of an adapter. However, keep in mind that these tubes are rare, more so than even the regular tripple triodes, so they are probably not a viable alternate solution. I'm just listing them here as a reference. -------------------------------------------------------------------------------------------------------------- Tube : Heater Plate Watts Max Plate V Max Plate mA Gain M. Conductance Plate Resistance 7688 : 6.3V 0.45A 3/3/3W 330/330/330V 11/11/11mA 17/17/17x 2200/2200/2200Gm 7700/7700/7700rp (6AV11 with different pinout) 7689 : 6.3V 0.45A 1/1/1W 330/330/330V 1.2/1.2/1.2mA 100/100/100x 1600/1600/1600Gm 62500/62500/62500rp (6C10 with different pinout) 7690 : 6.3V 0.45A 2.8/2.8/2.8W 150/150/150V 10/10/10mA 60/60/60x 5500/5500/5500Gm 10900/10900/10900rp (6AC10 with different pinout) There are other tripple triode tubes available. Both in Compactron and 9/10 pin miniature style tubes. However, they have their cathodes tied together which typically makes them unusable as a substitute for the tripple triodes listed above. Since these tripple triode tubes are configured differently they may or may not work in a rewired setup (none of them are direct replacements). Generally the difference is that they have two or all three of the cathodes tied together inside the tube. This can be either to accommodate fewer pins on the tube, or to satisfy specific design requirements. -------------------------------------------------------------------------------------------------------------- Tube : Heater Plate Watts Max Plate V Max Plate mA Gain M. Conductance Plate Resistance Notes 6EZ8 9KA 6.3V 0.45A 2/2/2W 330/330/330V 4.2/4.2/4.2mA 57/57/57x 4200/4200/4200Gm 13600/13600/13600rp (also 19EZ8) (6D10 in 9 pin miniature package) 6J9 10G 6.3V 0.45a 2/2/2W 330/330/330V 6/6/6mA 57/57/57x 5200/5200/5200Gm 11000/11000/11000rp (similar to 6D10 in 10 pin miniature package) 6MD8 9RQ 6.3V 0.9A 3/3/3W 330/330/330V 11/11/11mA 17/17/17x 3100/3100/3100Gm 5500/5500/5500rp (also 12MD8) (similar to 6AV11 but different connections) (9 pin Novar/Compactron) 6MJ8 12HG 6.3V 0.9A 3/3/3W 330/330/330V 10/10/10mA 17/17/17x 3000/3000/3000Gm 5600/5600/5600rp (similar to 6AV11 but different connections) (12 pin Compactron) 6ML8 9RQ 6.3V 0.675A 2/2/2W 330/330/330V 11/11/11mA 43/43/43x 6700/6700/6700Gm 6400/6400/6400rp (also 9ML8) (9 pin miniature - common cathode) 6MN8 12HU 6.3V 0.9A 3/3/3W 330/330/330V 11/11/11mA 50/50/50x 9000/9000/9000Gm 5500/5500/5500rp (also 9MH8) (12 pin Compactron - common cathode) -------------------------------------------------------------------------------------------------------------- Another possibility would be to use one of the dual triode/single pentode Compactrons with the pentode section wired as a triode. I have not actually explored this myself, so I have no idea if it can be made to work. For most of these, the pentode section is a power pentode used for verticle deflection circuits in TVs, so the chances of it working as a small signal amplifier triode is low. Here are the possibilities: 6M11, 6AF11, 6AS11, 6BD11, 6AK9, 6CA11 11CA11, 11CF11, 11BT11, 11CH11, 14BL11, 14BR11 15AF11, 15BD11, 16AK9, 16BX11, 23Z9, 31AL10 -------------------------------------------------------------------------------------------------------------- An alternate solution to the lack of available tubes is to rewire the circuit to accept more readily available miniature tubes. The most difficult tube to find is the 6C10. this tube is essentially a tripple section 12AX7 tube. So one possible solution is to replace it with two 6AX7 tubes or two 12AX7 tubes wired for six volt operation. However this will double the heater current which could potentially cause trouble, plus 6AX7/12AX7 tubes tend to be expensive. There are however other tubes that have the same characteristics as the 12AX7 that can be used instead. The 6AV6 is a single section of the 12AX7 with an added dual signal diode section. Just ignore the diode section, or connect the plates to the cathode. This will still cause the heater current to be slightly higher (by 0.3A), but the 6AV6 is commonly available and low cost. Alternately a 6BK6 could be used instead of the 6AV6. They are not as commonly available as the 6AV6, but are still low cost and have the same triode characteristics as the 6C10. If heater current is a problem, consider using the 6DR4 which has the same triode characteristics of the 6C10, but only 0.15mA of current, so three of them in parallel could draw 0.45mA. If you need to have exactly 0.6mA of heater current, then use one 6AV6 and two 6DR4 tubes. A little known 6V tube that has the same characteristics as the 12AX7 but with a 6V heater is the 6EU7. You could use a pair of these, or one of them and a 6AV6, 6BK6 or 6DR4 tube. Another little known tube that has the same characteristics as the 12AT7 is the 12DT8 The difference is that the 12DT8 has an internal sheild between the sections. The triode sections of the 12DT8 are exactly the same as the ones installed in the 12AT7. The 6DT8 tube is the same as the 12DT8 tube except the triode heaters are tied in parallel instead of in series. Or if you want to get wierd, you could use three 6SF5 tubes. The 6SF5 is a single section of the 12AX7 tube inside a metal tube with an octal base, or the 6F5-GT which is the same thing in a glass octal tube, or even the 7B4 which is the same thing in a loktal tube. There are also some other direct subtitutes for the 12AX7 that can be wired for 6 volts; 12AD7, 12DF7, 12DM7, 12DT7, 6681, 7025, 7729 however these are rare so you will probably not find them. There is also the 7689 which is a special version of the 6AX7 tube. If you are willing to rewire for an different filament voltage, that opens up the tube selection a bit more. That would allow the use of the 12AV6, 12BK6, 7058, 7689 tubes as well as the 12F5 and 12SF5 tubes. And one of the odder ones being the 20EZ7 which is a 20 volt version of the 12AX7 tube. If you cannot rewire the circuit, consider possibly using the 8AC10 in place of the 6AC10 as long as the heaters in the circuit are wired in parallel this will some times work ok, although as with the 6AC10, the gain of the tube is lower and with the lower voltage, there will be fewer electrons emitted from the cathode, so it won't work as well, but when there is no other alternative, it may be the only solution available.