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Friday, December 12, 2014

Tube of the Month : The 6BE3

Hi!

This post concludes the trilogy about the tubes used in the recently shown 6GE5 amplifier. Since the signal tubes both are 12-Pin compactron types it was only natural to select the rectifier from that series as well. And the chosen tube was the 6BE3.





Why another TV damper? Besides the various Octal types and the Novar 6CJ3, I already covered a 12-Pin compactron damper in the tube of the month series, the 6CG3.

The 6CG3 would actually be a bit overpowered for this amp. The 6GE5 only draws about 50mA. Even for a stereo version and taking additional current for driver and bleeder resistor into account, the 6CG3 would still be oversized. This is not a bad thing but it has the draw back of rather high heater current. The 6BE3 heater only draws 1.2A. The 6BE3 shares the same pinout with the 6CG3 which is shown on the left. It has a DC current capability of 200mA. This doubles when two of them are used in a full wave configuration. This is plenty even if some derating is taken into account since the 6BE3, as most TV dampers, was never specified for mains rectifier service.
Like all TV dampers, the 6BE3 was designed for extremely high peak inverse voltage. 5kV in this case. Again this needs to be derated for mains rectification. A derating to 50% still leaves a higher peak inverse voltage rating than most classic rectifiers. The 6BE3 is quite similar in it's characteristics to the 6AX4, the TV damper which I mostly use in power supplies. For the complete set of electrical parameters, please see the General Electric data sheet. While I have seen some 12-Pin compactors used in audio amplifiers, I never heard of anybody using a 6BE3 in the power supply. That's why they are sitting in the warehouses of tube dealers and collect dust. They can be bought for next to nothing, which makes them the perfect companion for the 6GE5 and 6AG9 in an amplifier. Here a photo of two 6BE3 in operation:




The 6BE3 was made by all the major manufacturers.

RCA:





Sylvania:






Sylvania / PhilipsECG:




Zenith branded (made by Sylvania):




General Electric:




DuMont:




Tung-Sol:




The characteristics of the 6BE3 are very close to the 6BZ3. In such cases it was a common practice to  combine the types and label tubes with both designations:




6BE3/6BZ3 made in Japan:





These came in a bulk pack of 50 pieces:




Now let's take this one apart to see how it is constructed inside:





Removing the glass reveals a better view of the plate structure:




The top side:




The white spiral provides isolation between the heater wire and the cathode.




Removing the heater with it's isolation spiral:




Close up:




The cathode:




The plate:






A 6BE3 in operation:




A close up to the heater :




I hope you enjoyed the last Tube of the Month post of 2014. Stay tuned for many more tubes to be covered in this series in the next year!

Best regards

Thomas

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