the ultimate guide to tube-rolling:
6550 / KT88 / KT120 / KT150

A range of power tubes for all tastes

6550 

The 6550 is a beam tetrode that's similar and often interchangeable with the KT88 and KT90. It was introduced by Tung-Sol in 1964.

KT88

A beam tetrode that is similar to the EL34. Introduced by GEC in 1956 specifically for audio amplification, and made by Shuguang, JJ Electornic, Svetlana, and New Sensor Corporation.

KT120 / KT150

Both tubes were developed for higher power from audio amps. The KT120 is a beam pentode, that, until the KT150 was the most powerful audio tube you could buy. The KT150 is an octal beam tetrode, and the egg-shaped glass helps dissipate heat and reduces microphonics.

Sovtek 6550WE

Sovtek 6550WE
$34.95

A rugged, reliable tube that offer a little bump in the midrange, tight bass, and good top-end extension.


Customer Reviews

A customer switching from the KT88 felt this had a lighter, airier feel. Customer's also report the tangible midrange presence.

Electro-Harmonix 6550

Electro-Harmonix 6550
$35.95

Kevin thinks this is a great tube that's really proved itself in the field.


Customer Reviews
One customer thinks it's even better than the EH KT88, and that's high praise. He doesn't think you can go wrong with any Electro-Harmonix tube in terms of quality and sound.


Electro-Harmonix KT88

Electro-Harmonix KT88
$38.95

Rugged and reliable, with great clarity and pop. On the neutral side. 


Customer Reviews

Customers report good bass extension, dynamics, and soundstaging. Good low-level detail and a linear dynamic response.

Tung-Sol 6550

Tung-Sol 6550
$38.95

A current re-creation of the classic original Russian 6550. Super dependable. Good bass, presence in the mids, and slight ease on top.


Customer Reviews

A good soundstage comes up a lot, as does good bass, and top-end presence without glare. One customer suggest this tube is the powerful love-child of a KT88 and EL34. "Liquid midrange, controlled bass, a smidge of roll-off in the highs." 

Mullard KT88

Mullard KT88
$44.95

Kevin thinks these sound a lot like the Gold Lion KT88, which come out of the same factory. Stunning mids, extended top end, tight bass.

Electro-Harmonix KT90

Electro-Harmonix KT90
$49.95

A drop-in for any KT88 or 6550 tube. Sonically they are true to the Electro-Harmonix brand; clear top end that is open but not bright or tizzy, tight bottom end, and a clear midrange that is not hard or clinical. They are not a super warm tube.


Customer Reviews

"A very refined, intimate soundstage with solid bass performance." Open and dynamic, full-bodied mids. A tube that can handle fast, complex music. Very accurate in the high frequencies, can tend to edginess in some systems. One customer suggests this is the tube to get if you want more power than the EL34, but don't want to lose any musicality and naturalness.

Tung-Sol KT120

Tung-Sol KT120
$49.95

A drop-in replacement for KT88s, rated to a plate dissipation of 60 W. But because they draw more filament current from your amp's output transformer, you should check with your amp's manufacturer to make sure you have enough headroom. Also, these are 1/2" taller than a typical KT88, so make sure you have enough clearance! Very deep, dynamic bass, a fast and open top end, and great sense of clarity in the midrange.  


Customer Reviews

One customer reports how he had to change his subwoofer settings because he got so much more bass. That and the increase in top-end response, dynamics, and soundstaging are reported to be immediate and dramatic. Amps struggling to drive difficult speakers relax and lose their top-end glare with these tubes. 

Gold Lion KT88

Gold Lion KT88
$59.95

Russian reissue of the legendary Genalex KT88. Sound is beautifully balanced... airy highs, gorgeous mids, deep dynamic bass.


Customer Reviews

Customers who are looking for EL34 magic with KT120 slam, find their home with these tubes. Customers who have had reliability issues with these when buying from elsewhere are pleasantly surprised by how long these last. 

Tung-Sol KT150

Tung-Sol KT 150
$107.95

Thunderously powerful. Tight, full bass, with a neutral midrange, and transparent, clear highs. Unbelievable dynamics. Buy KT150s from elsewhere and watch them drift out of spec until they are unusable in two weeks. We burn in all our power tubes, and then test them. Anything that's going to drift doesn't even enter our system--and this is after buying only the top 33% of production!


Customer Reviews

"More articulate while remaining smooth and rich, but it's the bass where things really take off." Customers report "pop" and "snap" and great bass with highs that extend forever.