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 Solid State Replacement of Tubes

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FrankB
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Join date : 2010-11-22

PostSubject: Solid State Replacement of Tubes   August 1st 2018, 8:09 pm

Thanks to a post from our newest member- Rod- it reminded me of a pitfall in replacing tubes, selenium, and copper oxide rectifiers with silicon diodes.

 I should have posted this before, my bad.  Embarassed

Diodes have much less voltage drop than tubes, or the mentioned rectifiers.
 So if you replace them you MUST! MUST! MUST! add a series resistor to compensate for the added B+ voltage.

The tubes often drop 20-30V internally and that added to todays much higher line voltages can cause havoc in older equipment.
   Filter caps can explode or short, causing other parts, like power transformers to burn up. (You have not lived until you see and hear a filter cap can in a piece of WW2 gear with a 16 ga. aluminum can blow apart and try to make like a rocket in a 1/8" thick metal radio case. The can lost well over 3/8" in height!  If you have ever tried to smash a piece of aluminum pipe that thick, you will have some idea of just how much force that can had when it blew, and tried to go into orbit. Shocked  Call it a real "brown pants" moment.) 
  Also, the cans can blow into sharp shards and cut you up pretty good. I have that tee shirt, cap and decal! Not to mention a trip to the Dr. to remove the shrapnel. I still have the scar under my eye, just below my glasses, and one on my arm as a permanent reminders.

So if you must replace the original type rectifier with silicon diodes be sure to add that dropping resistor, and take into account the higher line voltage too.

Hint: If you MUST replace the tube, try to put the parts on a tube base or plug so you (Or the next owner)  can easily change it back.

 On test equipment, if you change the B+ voltage, remember that a total re-calibration will be needed, especially on tube testers, signal generators, etc.
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