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Power Tube Matching

Click a question about power tubes to jump to the answer. You can always click the "Back to top" links to return to the question list.


1. How do I know I'm ordering a tube that is matched?

2. How do I order the right quantity of tubes?

3. Why do you match power tubes?

4. How are power tubes matched?

5. How accurate is your matching?

6. What does the Perfect Pair number mean on my matched power tubes from thetubestore.com?

7. Which of your power tubes have the Perfect Pair matching number?

8. Does my amplifier require matched power tubes?

9. What does it mean to "bias" the amplifier?

10. What about "early breakup" and "late breakup" power tubes that you see with other brands?

11. Can I use your power tubes in my Mesa Boogie, Fender, Marshall, etc. amplifier?

12. Do you match other tubes (for example, pre-amp tubes)?



1. How do I know I'm ordering a tube that is matched?

Most audio output/power tubes are part of our Perfect Pair matching system. These tubes will have a drop-down menu where you can select "Matched" or "Not Matched".
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2. How do I order the right quantity of tubes?
Common audio power tubes (output tubes) that we offer matching for will have matching options shown in the drop-down menu on the tube's webpage. If you require a matched set be sure "Matched" is selected. We will send you a matched set if you order 2 or more. For example when "Matched" is selected and you order "2" tubes, we will send a Matched Pair. If you order "4" tubes we will send a Matched Quartet. Typically we can provide Matched Sextets and Matched Octets as well.

If matching is not selected we will send un-matched tubes in the quantity ordered.
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3. Why do you match power tubes?

Many amplifiers are designed to require power tubes that have similar cathode current. Even tubes of the same type made at the same time will have variations in their cathode current, and this is why testing and matching is required. Please note that not every amp actually requires it - but it never hurts to have matched tubes. See this answer for more info about whether you need matched power tubes.
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4. How are power tubes matched?

Power tubes are paired up based on their current draw, or "plate current". Measuring plate current draw under operating conditions is generally considered to be the most accurate method for rating a power tube, and it is the method we use.
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5. How accurate is your matching?

We match tubes to be within 5% of measured plate current (that is, the tubes won't differ from each other by more than 5%, or 1 milliamp in 20).Despite what many people may say, this is about as accurate as power tubes can be matched. Tubes will always test differently from day to day because of fluctuations in the power supply and "drift" in the tube over time as it ages. When you consider that most electrical components in a modern amplifier are built with a tolerance of 10%, this is more than accurate enough. By contrast, common practice in the tube industry for the last fifty years has been to match power tubes to within 25%.
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6. What does the Perfect Pair number mean on my matched power tubes from thetubestore.com?

The Perfect Pair number is the actual "plate current" (see question 4) that we measured, using our digital matcher with a regulated power supply. You can use this number when ordering so that you won't have to re-bias your amp (more about bias later).
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7. Which of your power tubes have the Perfect Pair matching number?

We provide
Perfect Pair matching on the most common audio power tubes: EL34 types, 6L6 types, 6V6 types, 6550 types, KT88 types, and EL84 types.
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8. Does my amplifier require matched power tubes?

The best answer to this question is to consult your owner's manual. Reissues of vintage amps sometimes have substantially different circuits than the original, so it's difficult to make broad statements. 
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9. What does it mean to "bias" the amplifier?

Just like the idle of your car may need adjusting when a major change is done to the engine, new power tubes need their idle (the "bias") adjusted to make sure the amp sounds as good as possible. Some amps do this automatically, but many do not - particularly in the world of guitar amps.
Many tube amp owners are unaware of this simple regular service for their amp that will keep it sounding it's absolute best. The bias methods of amplifiers fall into several basic categories:

    - fixed adjustable-bias amplifiers

    - fixed non-adjustable-bias amplifiers (no bias adjustment pot)

    - cathode bias amplifiers

    Each of these types is unique. Fixed bias amplifiers can be either adjustable or non-adjustable. For adjustable fixed bias amplifiers, the amp should be biased by a tech with experience. It's not difficult and it doesn't take long but if you don't know what you're doing you may hurt yourself (amps can give lethal electric shocks even when unplugged, and NO, we're not just saying that to scare you). Also, your amp may sound horrible or cause undue wear and tear on the tubes or other amplifier components. Until you learn how to do it correctly by yourself, it's best to pay a technician a few dollars to do it for you. Non-adjustable fixed bias amplifiers without a trim-pot cannot be bias adjusted without changing the resistors in the bias circuit to different values. So for practical purposes this is considered non-adjustable. These amps (for example, all Mesa Boogie models) use a fixed resistor to bias the tubes, not a bias pot, and are designed to run with tubes that have a specific current draw range and should only use tubes that fall within that certain range. Fortunately, these amps are usually very forgiving and will work well with a pretty wide range of tubes. For the best results, specify the make and model of your amp in the "Comments" of your order and we will make sure you get the best tubes for your amp.

    Cathode bias amplifiers shouldn't require any adjustments and will work with a wide range of tube plate currents, as the circuit is "self adjusting".
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10. What about "early breakup" and "late breakup" power tubes that you see with
other brands?


One important aspect of this concept is to keep in mind that it only works in fixed bias amplifiers. For comparison to the Perfect Pair numbers, lower numbers have "early breakup" (distort more easily) and higher numbers have "late breakup" (distort less easily). You can specify this in the "Comments" section of your order, and we will make sure you get tubes that have the desired effect.
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11. Can I use your power tubes in my Mesa Boogie, Fender, Marshall, etc. amplifier?

Yes. We sell tubes from the same factories that provide tubes to amp manufacturers. Like original parts for most equipment in the world, they tend to charge extra for spares and so ordering tubes from us can save you quite a bit of money. For guitar amplifiers, telling us the make and model in the "Comments" of your order is enough for us to supply you with the right tubes. For home audio, nearly all amps can take the full range of current tube production. There are rare cases where certain tubes won't run in some home audio amps, and that's what our 90 day exchange policy is for.
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12. Do you match other tubes (for example, pre-amp tubes)?

There are some circuits that can benefit from matched preamp tubes. However, in many cases it can be difficult to discern any improved sound quality. Regardless, we do offer "Matched Sections" matching service for common preamp tubes such as 12AX7, 12AT7, 6922, etc. The price for pre-amp tube matching is $5 per tube and not refundable. Power tubes require matching because the way they amplify signal can create exceptionally bad sound if they are poorly matched, but pre-amp tubes generally aren't used this way and so matching them is unnecessary.
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