It is never a bad idea to have spare tubes around for your R390A or even a "junker" parts radio.  Even though the receiver was designed and built to the highest quality mil-spec standards using silver plated contacts, all stainless steel hardware, modular construction with industrial grade vacuum tubes, they can and do fail.  Clamps break, transformers short and get noisy; the spare receiver I bought for $50 a few years ago as well as a complete stock of replacement tubes has proven invaluable the few times mine has actually needed repair.

Below is the full suite of vacuum tubes used in the R390A.  I suggest obtaining at least 2 complete suites of tubes while they are still reasonably priced. Even better to have 4 complete sets on hand.  Make a few copies of this page and take it with you to the next hamfest.  Always try and purchase the industrial tubes.  These are the underlined numbers.

R390A Vacuum Tube Suite - Quantity needed and 1996 market price
 

6AK6  (3)                $2-$5                                                        5654/6AK5 (2)         $2-$5
5749W/6BA6 (6)     $2-$5                                                       5814A/12AU7 (7)     $2-$9
6100/6C4  (3)          $2-$5                                                       26Z5W (2)                $10-$20
6DC6  (1)                $5-$10                                                      3TF7 (1)                    $20+
OA2   (1)                 $5-$10
 
 

Total Tube Count: 26

Right now, tubes are not as difficult to find as some might say.  On the other hand they are largely no longer being built so, the number of available tubes is finite.  Consider building your stock now while prices are still reasonable.  A goal of having at least 4 complete sets on hand sounds like a lot but its a reasonable capital investment if done over time.  Always try and purchase JAN/Industrial grade tubes.  These are found in plain, white boxes, are labeled JAN and also show the date of mfg on the box.  In the case of the 6BA6, 12AU7 and 6C4, try and purchase the 5749, 5814A and 6100 respectively which are premium tubes with JAN/Industrial specifications.
 

Page prepared by R. Charles Rippel

E-mail to: Charles Rippel
URL: http://www.R390A.com
Revision: 03 March 18, 2001
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