Some quick and dirty subs and some tube data such as recommended bias current and appx voltages. These subs are all taken from the Tube Substitution Handbook sold by Antique Electronics Supply. or provided from the net.
A (short) catalog of tubes you are likely to see in a guitar amp:
- 12AX7[A, WA] and substitutes - preamp and driver tubes
- 12AT7, 12AU7 and subs, preamp and driver tubes
- 12AY7 - driver tubes
- 6EU7 - dual triode used in some older amps for preamp tube
- 6L6 types - power output tubes, up to 50 watts/pair, a mainstay of Fender
- EL34 - Euro power pentodes, up to 50 watts/pair, many Marshalls
- 6V6 - smaller, lower power cousin of the 6L6, 10-14 watts per pair; used in smaller Fenders
- EL84 - fits a 9 pin socket like a 12AX7 but twice as tall; miniature power pentode, good for 12-18 watts per pair; used in smaller Vox amps, and a quad of these drives the Vox AC-30 for 30 watts.
Substitutions:
- * means appropriate for parallel filament circuits
- # means may not work in all circuits
Preamp and driver tube substitutions:
- 12AX7 (high gain dual triodes with pinout 9A)
12AD7* 12DT7 772912AU7# 5751* B33912AU7A# 5751WA* B75912AX7 6057 CV400412AX7A 6681 E83CC12AX7WA 6L13 ECC80312BZ7* 7025 ECC8312DF7 7025A M813712DM7* 7494
- 12AU7 (moderately high gain dual triodes with pinout 9A)
12AU7[A,AW,] 6189 773012AX7* and subs 6670 ECC1865814[A,AW]* 6680 ECC8025963 7316 ECC826067 7489 M8136
- 12AT7 (medium gain dual triodes with pinout 9A)
12AT7[many suffixes] 7492 E81CC6201 7728 ECC8016679 A2900 M8162ECC81 B152 QA240612AZ7[A]* B309 QB3096060 B7396671 CV4024
- 12AY7 (low gain dual triodes with pinout 9A)
12AY7(and suffixes) 60722082
Power tube substitutions:
- 6BQ5/EL84 (miniature pentode with pinout 9CV)
6267 7189 EF866BQ5 7189A EL846BQ5WA 7320 N7096P15 E84L Z729
- 6L6 (beam power tube with pinout 7AC)
6L6(many suffixes) 7581(A)5881 WT65932 EL37
- EL34/6CA7 (power pentode with pinout 8ET)
EL34 12E136CA7 KT777D11 KT88
- 6550 (power pentode with pinout 7S)
6550[A] 7027A#7D11 KT8812E13
Cautionary Tubes - these are very hard to find
- 7591/7591A - legend has it that these otherwise excellent tubes were all bought up by an oriental buyer who toured the USA paying cash for all of them he could find, then disappearing. You are likely to only find used ones or the odd pair in some out of the way place. Dealers will in general not have them. I have personally seen trays full of NOS 7591A's for sale in the Akihabra electronics district in Tokyo, lending some credence to the rumor.
These were used a lot in old Ampegs. They are very small and high gain for their physical size, so there may not be a lot of room in a chassis for a larger replacement. The 5881 will work in some circuits, but has significantly lower transconductance.
Rumor Update: The rumor mill on the net says that the Russians will soon be making 7591's soon. Cross your fingers...
- 7199 - combination pentode/triode used as a one-tube voltage amp/phase inverter/driver for a pair of output tubes in some Ampeg amplifiers Note: These were once popular, but are now getting rarer and more expensive. There are a number of other pentode/triodes that can be substituted, but the pinouts are different and this will require require rewiring the socket for the tube. Examples are the 6AN8 and the 6U8. There is a Russian tube that is labeled 7199 which may work, although this is new.
- 7027/7027A - this is a high power tube similar to a 6550. The supply of these is very poor.
- 7189/7189A - a higher power/voltage version of the 6BQ5/EL84. Hard to find. A stock 6BQ5/EL84 may work if the power and voltage conditions in the amp are not right out at the limits of the tube design.
