Audio Innovations 500

Tube Info

Standard the AI500 came with valve's from Precision. There are a lot of valve's that are better than these OEM valve's. All the tubes used in the AI500 can be replaced with a different type. The table below show you which type of valve's can be used without the need of modifying the circuit of any Audio Innovations tube amp.

Valve	Substitute	Do not substitute
ECC-83	12AX7 - M8137 -12AT7 - 5751	ECC88
ECC-82	5814A - M8136 - 12AU7 - E82CC	ECC88 - E182CC
ECC-88	E88CC - 6922 - 6DJ8	ECC82 -ECC83
6922	-	ECC-88 (relates to P1 Phono stage)
EL34	5881 - 6L6GC - KT66 - 6CA7	6550 - KT88 -KT90
2A3	-	6B4G
6B4G	-	2A3
EZ80	EZ81 - 6V4	-

It's very difficult to say something about the sound of a tube brand in general. A for instance a Philips ECC-88 will sound different from a Philips ECC-83. Although I tried to find out some general characteristics of some well know brands and put this in a schema. This schema can give you a hint on how a tube of a specific brand will sound. Of course it also depends on the equipment the tube is used in (the actual amplifier) and the task of the tube. An ECC-88 will probably sound different as a fase inverter than as a line driver.

I have listened to a lot of valve's. In the table below you can find my findings of some valve's i've reviewed. Of course these findings are personal but hopefully it can help you find a replacement valve for your original.
This list is updated regularly... If you first want to know how a tube works, click here.

Powertubes:

Valve	Picture:	Sonic characteristics:
EL34 Unkown brand (used as reference)		These are the tubes I use myself. They're real good tubes in my opinion. The best EL34 i've heart so far. These tubes have no text or type printed on the glass. Have seen them with many different brand names on it. They measure like a Genaral Electric EL34, so I can not say for sure it's a GE EL34 or from any other brand. They sound very detailed and open. Good bass and good treble. If you want these, mail me. ( I still can get them )
Svetlana SV-EL34		I had to try these because of there good reputation. There a bit softer and rounder in the top and has a less open stage and bass than the tubes used for reference. Details are good. This tube is still being made by Svetlana. One of the best you can buy if you don't want NOS.

ECC-83 / 12AX7 types (used as line input driver or phono):

Valve	Picture:	Sonic characteristics:
General Electric Jan 5751 (used as reference)		While not really a 12AX7, it shares the same pin-layout and is designed for less gain in favor of lower noise and microphonics. It works fine in the AI500. Very little notice of the less gain. This tube has 70% gain of the original 12AX7 / ECC-83. The sound is warm and very open. Good bass, mids and top. There not expensive (yet). A hell of a bargain for your amplifier.
General Electric Jan 6072a		Again not a real 12AX7. It's a 12AY7, which means its pin compatible and has 45% gain of a original 12AT7. These valve is recommend to me for use in the phone section. I tested it in the line input like all the other tubes. Some people say this is the best you can get. Not in my opinion. This tube lacks mids. Top is warm and not very detailed. Less open stha than the GE 5751.
Mullard M8136 (CV4003)		This tube has a very deep stage, but sounds has not the open stage that i expected. Sound came a bit more from the speakers, sometime's creating a gap in the middle. Sonically it has a real nice sound. Dynamic and a bit bold. Placement of the instruments was a disaster. In my opinion a strange sounding ECC-82 substitute with positive and negative sides.
Brimar 12AT7		Brimar is slowly becoming just as famous like amperex & mullard. This tube is made in england. The bass is strong and has punch. The treble can be a bit excessive. A good tube if your system can use a bit more treble. This tube is the most dynamic one i've ever heart. Details are nice to. The stage sounds upfront and but not as open as the GE 5751. Very suitable if you like voices & pop music. Not expensive. Try it.
Brimar CV4068 (6158)		Scheduled for testing
Telefunken ECC-83		Telefunken tubes are very well know by audiophiles. They are expensive, because most old stock is gone. This tube is a 17mm smooth plate type. It seems this Telefunken has it all. Very extended and bright top, but never aggressive. Very good stage. The bass is tight and has punch. Mids and detail are great. This valve is also very dynamic and sounds extremely open. It's just incredible... I don't want to use anything else than this tube.
Telefunken ECC-81	No Picture yet	Scheduled for testing
Raytheon CK6072A	No Picture	Very well build tube. Not 2 but 3 spacers are used. This tube is used in the famous ongaku amplifier from audio note. It sounds like the telefunken, but with a slightly less bright top. Stage is wide, open and detailed. It sounds a bit more civilized than a telefunken. Very nice tube.
Siemens ECC-83	No Picture yet	Scheduled for testing
Philips ECG Jan 12AT7WC		Less bass, copper sounds soft. Not as bright and spacey as the tubes used for reference.

ECC-88 types (used as phase inverter):

Valve	Picture:	Sonic characteristics:
Philips ECC-88 (used as reference)		This philips tube is not a modern ECG type. It sounds a bit bold in the mids, but with good details. Soundstage is very open, precise and spacey. Top is bright without being hars, and the bass is tight with a good punch..
Philips Miniwatt E88CC		Scheduled for testing
Siemens E288CC		This tube is higher in length than an normal ECC-88. It's a rare and expensive tube. The sound shows great detail and an open sound stage. It sounds less bold and more civilized than the Philips used for reference. This is a tube for people who wants the best of all.
Mullard E88CC	No picture yet	This tube has a good tight bass. Voices sounds nice and upfront. The stage is less wide than the philips used for reference. This tube takes me less to the hifi heaven, because the sound does not get me. In some cases this tube can be very microfonic. Use a good damper if so ! Mullard has a real good name, but it seems not to be my cup of tea.
Sovtek 6922		This tube is probably the most used tube by manufacturers. Many brands use this brand and type as OEM tube in there equipment. I know true my own experience that this tube is good but sonically there are many better tubes. So if you want to make your amp better sounding, replace this one. A philips will sound brighter with more space and better detail. If the philips is better overall is for you to decide. This tube sounds a bit warm and laidback at the top. Other brands will probably sound more precise.
Philips 6DJ8		Less space and detail than i'm used to hear. Less bass, dynamics and depth. This tube sounds a bit boring and stuffy to me. A bit brighter than a Sovtek 6922. If you're playing with a 6922 and seeking for a brighter sound and don't have much money to spent try this one. There easy to find and not expensive. Musically I prefer the Sovtek 6922.

If you want to experiment with tubes in your amp, follow these rules.

1. Make sure the amplifier is turned of and the valve's are cooled down.
(a hot valve is very sensitive for failure)
2. Use coton gloves or something to handle the valve's.
3. Make very very sure you're changing the valve with subtitute or same type.
4. Always give a valve time to get warm-up and develop his sound. (Approx 15 min.)

Some tubes listed above are for sale. Send me a mail for your questions..