Kt77 vs El34: Differences You Need To Know

A common tube replacement question is whether the kt77 tubes is going to be an improvement over the el34 tubes.

In this article, we are going to compare their differences as well as understand about their history.

Their main difference is that kt77 tubes have more headroom, detailed highs as well as bigger bottoms than the el34 tubes. kt77 tubes also are more dynamic in sound and suffer from less compression. However, el34 tubes are more durable and slightly less expensive.

If you are a beginner, the above differences might not even be obvious too you. In the mid range, both sound similar. The differences only becomes obvious in highs and lows. Unless you spend a lot of time playing in these 2 extreme areas, you can’t tell the difference.

In short, if you are want tubes that give you better audio sound, you are going to have to pay for it in terms of slightly higher prices and shorter shelf life.


Can kt77 replace el34?

The answer is yes for the below amps which has been tested in forums around the web:

  • Marshall DSL’s, TSL’s and JVM
  • Pevey JSX amps
  • Peavey amps with XXX numbering
  • Mesa Rectifier amps
  • Orange MKII

Out of the above, the kt77 has the most obvious improvement in Marshall amps. The tone complements Marshall’s natural tone perfectly.


How to bias kt77

Once you have decided to change your el34 for the kt77, the next step is to bias the latter.

Without the right biasing, your tube might be under or over biased. Under bias will reduce the power level while over bias might over heat your tube.

Here is how to bias a kt77.

  • Kt77’s natural bias is set at 0.4 to 0.5
  • Start the 0.4 and listen
  • Adjust at 0.05 increments to find the best sound output
  • As long as you stay in the designated bias setting, your kt77 tubes wouldn’t get over heated
  • Side note: check your wall voltage. The higher the voltage, the more it will change your tube’s bias settings. It is best to keep the wall voltage to as close to the recommended as possible

Some extra safety steps you should know before doing the change:

  • Be extra careful around tube amps as they carry a higher voltage. Do not touch anything else beside the tubes!
  • After changing, monitor the tubes to ensure they do not glow red. If they do, it means the bias is set too high and there might be a tube burst.

Gold lion kt77 vs JJ kt77

One particular issue that might come up is which brand of kt77 tubes to buy. Currently, there are 2 prominent brands with kt77 tubes: gold lion and JJ.

Editor’s note: The gold lion kt77 is referring to the reissue, and not the original.

Their main difference is that gold lion kt77 tubes sound more dynamic than the jj kk77 , which sounded more one dimensional. They also have more lows, which make them sound louder. However, the JJ kt77 tubes prices are about one third of the gold lion.

Here is useful video that can let you hear their differences:

Which is more durable?

Another key difference is their durability. This is where the community is split on. On average, most feel that JJ kt77 tubes have a shorter shelf life. They need to be replaced usually after 9 months to a year. However, this is not universal and may depend on particular production batches.

You can read more from this forum for example about how bad the JJ kt77 shelf life is: https://www.rig-talk.com/forum/viewtopic.php?f=14&t=203517

Another possible reason for the frequent failure of JJ kt77 tubes, according to a knowledgeable forum member, is :

“The tube life issue may have to do with the tube socket grid bias resistance value with regard to the 250k limit of the JJ KT77 reported by JJ Electronics, at least partially due to the absence of the pin 1 connection they chose for compatibility with Fender Twin amps.”

In contrast, I have not heard negative thing about the durability of gold lion kt77. My own personal experience is that they can last more than two years.

Which is more biased

The JJ kt77 are designed to be as electrically compatible as possible. Hence the sound they generate will be similar to what comes after the type in power. This is why they are more full sounding.

In contrast, the gold lion re-issued kt77 is meant to model after the original gold lion. As such, they are biased at the 70% to be brighter.


Short History of KT77 and El34

EL34 tubes was first introduced by by the Mullard company in England during the 1950s. It became popular pretty quickly. In a way, it contributed to the increased popularity of tube amps.

Then came the 6CA7, which was created in America. It was designed explicitly to be easily used as a replacement for the el34.

Due to this increased competition, the kl77 tubes were invented. In a way, this represented what the el34 was trying to be when it was invented. Due to this much improved design, the resulting audio became more refined, as described above.

With this understanding, it is easy to see why the kt77 is a good replacement tube for the el34 tubes.



The change from from el34 to kt77 will not magically change your tone, say from less metal to more metal. What it does improve is the following:

  • More headroom
  • Sharper highs
  • Generous bottoms
  • Less compression

If these improvements sound good to you, then getting kt77 as replacements for el34 is a worthwhile investment.

4 Comments Posted

  1. I tried to use GL KT77 on Cary CAD805 and I love the sound. Indeed, more headroom,detailed high & better low. But one of the tube went bad within few days. From your article it seemed to adjust the bias is the key, but I do not see any place that allows to run bias adjustment. Do I need to buy any instrument to do the self-adj?

  2. Thanks so much . my amp Audio Space as 3i 10 years old . Changed out the original EL 34 a year ago for JJ KT 77.
    Set bias at .46 DC Volt . They just are Marvellous sound totally full range dynamic balanced sound 14 months $168 quad part
    On Amazon.CA. I I’ll b another pair when these die

  3. This is an excellent in-depth review of EL34 VS KT77 tubes. The reviewer certainly shared good knowledge in this areas both technically and musically. Your review did answer many of my questions about both tubes. Thank You so much

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