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Monday, February 5, 2018

Tube of the Month : The 82


This months tube is a mercury vapour rectifier, the 82.

The 82 is the small sister of the 83. While the latter is quite popular, the 82 seems to be completely forgotten.

The main reason for that might be the lower current handling capability of the 82. It can only deliver about half the current of the 83. But that would be sufficient for low power single ended amplifiers using tubes like the 45 or 2A3. The 82 has the same pinout as the 83, see diagram on the left. It also requires the same hefty 3A filament current but with only 2.5V, half the 83s filament voltage. The 82 is also physically smaller, while the 83 comes in the ST-16 bulb, the 82 has a ST-14 bulb like the 45, which again would make it a suitable choice for such an amp for physical appearance. It could also serve as rectifier in preamplifiers of course. Like all mercury vapour tubes the 82 is preferably used with a choke input filter. Although it can be used with cap input as well if precautions are taken to limit the peak current to the maximum value of 400mA as specified in the RCA data sheet. Although I never used the 82 in a project, I acquired a small stash of them over the years. Let's have a look at some of them.

First some samples made by RCA.

In this type box the tube is held in an extra card board sleeve inside.

The tube has the typical full wave rectifier structure with the two plates mounted in parallel inside the bulb.

Close up:

The top:

Slightly different style RCA packaging:

Close ups showing the two supports on either side at the base which held getter material and the mercury during the manufacturing process of the tube:

The typical getter holder on the right and the little pouch on the left held the mercury.

Raytheon also made the 82:

This tube had a clever packaging which ensured that no used tubes were resold in the box.

The tube could not be removed without tearing the inner carton.

And the packaging allowed to test the tube while it remained in the box. The inner carton can be pushed out a little so the tube pins are exposed and can be plugged into a tester.

These Sylvania boxes had a similar sealing:

Since the seals on these boxes are still intact I did not want to remove the tubes.

Older style Sylvania boxes without seals:

A 82 made by General Electric:

Here a 83 and a 82 to show the size difference.

The 82 was also made in the ballon shape glass, here an early RCA:

The tube is securely wrapped inside the box:

And comes with a spec sheet.

Gorgeous globe shape:

Unlike other globe tubes this one does not have a three digit designation.

Close ups:

Another globe 82, branded RCA Cunningham:

Now let's see how it glows. When the heater voltage is applied the mercury starts to vaporise:

And when high voltage is applied the blue glow appears inside the plates:

View from the bottom:

An interesting small rectifier! I hope you enjoyed it.

Best regards


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