2. amps-preamps
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Spare tubes? How many?

Being the anal sort of worrier that I can be, I'm thinking to buy some back up tubes. 4 KT88s, 2 12AX7s and 2 12AT7s in place now. I believe only the power tubes are really prone to fail. Welcome correction if I am wrong in that assumption. Should I buy 1, a pair or a complete Quad set of KT88s. If only one tube fails (assuming no sort of catastrophic fireworks) can you simply replace the single and re-bias? Will that make everything OK? (tubes were purchased from the Tube Store so are matched and have the matching number). Thanks for the input.
GH
128x128ghosthouse
thorman
1,262 posts
 
always have a full set ready and a used pair ( that still work ) ..Always keep your last working set ( thats just tired ) ...Accidents can happen!! I keep 1 fresh complete set and 1 tired set...I use EL34 ( quad ) 2 pairs 12at7, 1 pair 12bh7a and 2 12ax7...
newbee
4,775 posts
 
Any tube can fail, especially if you don't have a spare.

If you have individual biasing pots for each tube replacing the blown one and rebiasing it works fine, so long as you're not too anal. You don't need to replace the other three. Now if the tubes have been used a lot you can replace the entire quad and have 3 'spares' for future failures. :-)

Seriously, the small tubes die unexpectedly, even though they typically have a long life. At least keep a few new production tubes available to keep you in music until you can get some replacements.
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