Treasure KT88-Z CB Cobalt Blue Bottle Super Tube (GF-Select, Quad)

A brand new addition to our KT88 offering with a ‘blue’ twist!

This KT88-Z CB is another step of progress over current high end KT88 tubes on the market. It adopts a cobalt blue glass enclosure to provide better heat dissipation through the glass enclosure. The new model number is called KT88-Z CB – Cobalt Blue bottle. The transparent blue glass allows you to see tube glow but not overly bright to distract listener.


– A true super tube: 25% more cathode effective area, improved cathode material, which lead to 25% stronger electron emission

– 600V High voltage factory long hour burn-in to allow less impurity and less intrinsic baseline noise, and more stable performance over long lapse of time

– Same glass enclosure size as standard KT88 tubes to be interchangeable with all KT88 on the market

– Gold pin / improved metal base leaves no smudge



How does it sound? We did an in-house preliminary comparison to other high end KT88 tubes we have on hand – we feel instrument separation has been greatly improved, and high’s/low’s extension has noticeably improved too. You may have to take the plunge to let your ear tell you how they sound for with your system!


Below is how the KT88-Z CB compared to KT120-Z CB in terms of size:

Suggested Break-in Time:

Please note: This tube requests extended break-in time to sound to the best. Recommended 150hrs.

Special Note when placing an order: 

As our KT88-Z CB has stronger plate current than some KT88 tubes on the market, some amps with auto bias circuit plus auto shut-off protection circuit may wrongly take the high plate current as false internal short, so the amp may shut down automatically into protection mode. This doesn’t mean the tubes are defective – strong current is a positive thing in new tubes.

When placing order, please make sure to select the ‘bias mode’ as either ‘Self bias with auto shut-off circuit’ or ‘manual bias’. In general, manual bias amp can accept higher plate current tubes (the higher plate current will also allow tubes to have longer aging time). We will select tubes based on this information provided so that the tubes shipped to you will best suite your amplifier.

All KT88-Z CB tubes for the time being will be shipped out of Grant Fidelity Canada office, tested on Amplitrex AT1000, and run active on an amplifier for 8 hrs before shipping. Please kindly allow us extra time to selecting and shipping your tubes after the above mentioned process.

Stock Status: 

In stock now for immediate shipping from Canada to worldwide. 

This model comes with additional 90 days warranty on top of our regular tube warranty. Buyers have 180 days from purchase date for warranty against any manufacturer defects. We hope this gives you extra confidence in experimenting the KT88-Z CB Super tube sound ? 

Please select:

Price: $495.00
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