I came to know the name of Pearl Cooler and IERC heat sink for tubes from one Hi Fi magazine some years ago. Both operate as an add-on device for tube, and their outlook design and operating way are similar to the fashion of condom for human. So, you may simply call them “Tube condom”.

Pearl Cooler

This metal bodied tube condom is made in Canada. As far as I know, Pearl Cooler is available in 2 sizes of the same colour in the market.

The one you can see in the photo is a small-size Pearl Cooler, which is used for pre-amp tubes, such as ECC83, 12AU7, 6DJ8, and 6922. The large-size one is meant for those power amp tubes, like EL34, 6L6, 5881, 6550, etc. 

How to use it?

Very simple and easy, just dress it up on a tube top-down, like the condom way. As you can see from the photo too, Pearl Cooler comes with a black coloured rubber band. This rubber band is provided for operating with Pearl Cooler, for tightening up the Pearl Cooler to the tube body. 

What is it for?

 In general, Pearl Cooler is made to serve three functions as follows:

• To Reduce the microphonics generated from tubes, by stabilising them when they are on and performing.
   
• To Protect the tube from distortion caused by the surrounding RF.
   
• To Enable Faster Release of heats generated by the tube, so as to enable the tube to operate for longer hours as well as for extending its lifetime.

Some people are also utilising it to fine-tune the sound from their pre-amp. 

Any operating tips? 

I have been using the small-size ones for pre-amp tubes since the day I bought them. I found that Pearl Cooler really functions as what it is made for. Nevertheless, there are still some operating tips for optimising the Pearl Cooler’s performance that I would like to share with everyone.

Don’t use the black coloured rubber band with Pearl Cooler at all. When added, it gives tightened, fast and powered sound effects but in an unnatural way, like being squeezed out. It has also some offsetting effects on sweetness, clarity and crispy from the soundstage.

Use a crocodile clip with a wire for connecting the Pearl Cooler to the ground terminal of the amplifier (refer to photo). You may also add on a RF or digital sound absorber clip for each wire as shown in the photo. This is an effective way to eliminate microphonic effects and RF interference. 

IERC

Another type of metal made tube condom I ever tested is the IERC (International Electronic Research Corp) , which is made in US and is said to be for military usage. IERC has the same functionality as that of Pearl Cooler. When added, it gives the same sound effects as from Pearl Cooler with rubber band, but in a slightly moderate way. As its overall performance is not better than Pearl Cooler, I did not use it for my pre-amp tubes anymore. 

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