Type 5963 is a 12AU7/ECC82 specified for computer  use. 5963 tubes will work in all 12AU7 / ECC82 applications.  

Although nominal maximum plate voltage is 250 volts compared to 12AU7 rating of 350 volts, this does not affect performance and they can be used with confidence in place of 12AU7. Type 5963 is a 12AU7 variant originally designed for use in tube computers. It has a special cathode coating to avoid loss of emission when operated for long periods under cut-off conditions. This gives greater reliabilty in digital tube circuits.  

This pic http://www.retrovox.com.au/Images/hpdfc.jpg shows the inside of a Hewlett-Packard all-tube digital frequency counter with twenty 5963 tubes!
The weight of this item is listed as: 10.0
The price of this item is listed as: A$11.00 each

email c20store@retrovox.com.au for enquiries or orders

PAYMENT: Retrovox purchases can be paid by Visa or Mastercard,PayPal or direct deposit (wire transfer). Australian buyers: No PayPal. Direct deposit preferred for Australia buyers.

DELIVERY & PACKING:Delivery by Australia Post Airmail. Worldwide delivery takes about seven days. All orders are carefully packed to withstand any foreseeable shipping trauma. Retrovox has shipped thousands of tubes and parts worldwide with a perfect 'no-break' delivery record for over eight years.