A Short History of the KT88
As the vacuum tube gained in popularity and use, competition arose between U.S. manufacturers and European manufacturers to produce new tube types. Out of this competition arose the EL34, the 6L6, the 6550 and the KT88.
The original KT88 was produced by GEC in 1956 also labeled as IEC/Mullard, or Genelex Gold Lion. It was the European answer to the American 6550 tubes, and was specifically designed for audio amplification. The KT88 is also one of the largest vacuum tubes in its class.
JJ-Tesla KT88
Current production of the KT88 is limited to factories in China, Slovakia, and Russia. These include JJ-Tesla, Genalex Gold Lion reissues, as well as Sovtek, Electro-Harmonix and the newly available EAT tubes. Original production, unused (NOS) KT88 tubes in good condition are increasingly rare and expensive, sometimes costing $900 or more a pair. Historically these tubes have been more popular in hi-fi stereo equipment than in guitar amplifiers, since it provides high power and low distortion. Guitar amplifier owners will regularly use them to replace 6550 tubes, particularly if they want less distortion.
The KT88 fits a standard eight-pin octal socket, has can be used in similar applications as the 6L6 and EL34, since they have the same pinout.
From the original GEC description, points about the KT88:
1. The KT88 is a beam pentode with aligned grids for maximum efficiency.
2. 50 watts output is available from a pair connected in the ultra linear circuit with auto bias and an HT line voltage not exceeding 500.
3. 100 watts output is available from a pair connected in the ultra linear circuit with fixed bias and an HT voltage not exceeding 560.
4. 25 watts output is available from a pair triode connected with auto bias and an HT line voltage not exceeding 500.
5. The mutual conductance of the KT88 is 11mA/V
6. An all-glass ring seal replaces the conventional pinch seal giving increased strength, higher rating and reduced dimensions.
7. The valve is mounted on an international octal base and has a heater rating of 6.3 volts., 1.8 amps.
If you use KT88 tubes, tell us what you think. How do you use them? Which brand do you prefer?
We look forward to hearing what you have to say.
Tags: KT88, TubeDepot.com, Vacuum Tubes
February 1st, 2009 at 11:22 am
I think KT88 from china really ugly tubes.
JJ - so so… better old TESLA.
My opinion Electro Harmonix - one of best modern.
March 19th, 2009 at 3:07 pm
I use KT88s with E34Ls both by JJ-Tesla in one of my Randall RM100m heads.
I love this tube, it is rich and full and is great for all types of music. I play all metal stuff and the ocassional blues lick, and these tubes sound superior to most tubes i have tried. I use Mesa EL34 and JJ 6L6GC in my other RM100 head and the combo of both heads makes for great tonally possibilities, if you havent tried a Randall MTS RM100 you should.
KT88 tube is flawless.
March 19th, 2009 at 5:20 pm
I have a matched quad of JJ/Tesla Blue Glass KT 88’s and they made a huge difference in the sound quality. The bottom end immediately became much more open and the sound was far better. The amp came with Chinese KT 88’s. My opinion only, but I tried Electro Hamonix and did not like the sound at all.