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Tube purchase practice

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Posted on October 31, 2009 at 10:53:04
bdgregory
Audiophile

Posts: 180
Location: Mid-Atlantic
Joined: July 30, 2005
 I suspect this may have been addressed before but I'm at a loss to find the thread. So forgive me for the new thread . .

My Question:
What is your practice when buying power tubes? Do you buy 1 or 2 spares matched to the quad at time of purchase, or buy single replacements if/when one fails prematurely?

I have an amp that uses a quad of EL34s or KT88s. It seems inevitable that one of the four will fail long before the normal life span (but last past the warranty period).

thanks in advance!
RE: Tube purchase practice, posted on November 1, 2009 at 07:20:05
bdgregory
Audiophile

Posts: 180
Location: Mid-Atlantic
Joined: July 30, 2005
 thanks again to everyone!

How does your amp bias the power tube?, posted on November 1, 2009 at 01:29:49
FenderLover
Audiophile

Posts: 3313
Joined: July 31, 2007
Contributor
  Since: May 17, 2009
 For Class AB1, push-pull amps: If it biases each push-pull pair, you can get away with spare matched pairs. If it biases one channel--- and each channel has say 4 tubes--- then you need matched quartet. If you are lucky enough to have a bias pot for each tube, then "close" enough is ok between power tubes (you don't need 15-20% tolerance, which seems to be abitrary "matched" standards).

Strong testing tubes which are close tolerance (equal or < 10%) are prolly going to sound better, due to reproduction of the music's signal and not simply idle bias parameters.

RE: How does your amp bias the power tube?, posted on November 1, 2009 at 07:18:17
bdgregory
Audiophile

Posts: 180
Location: Mid-Atlantic
Joined: July 30, 2005
 thanks, the particular amp in this case has a bias pot for each tube, but I have other amps (both audio and guitar amps) that have a single pot per p-p pair, or are cathode biased.

RE: Tube purchase practice, posted on October 31, 2009 at 11:56:24
Dangerbird
Audiophile

Posts: 46
Location: hot 'laanta
Joined: December 28, 2006
 I have a spare for my amp,, yours is a good idea,,I think,, but I usually buy a matched quad,, keep the best one of the ones I'm replacing should I need it,and it goes into the backup box.Now if there was only a way to predict the lifespan of power tubes,I'd be ahead of the game.

RE: Tube purchase practice, posted on October 31, 2009 at 12:22:13
Ron Oehlert
Audiophile

Posts: 4649
Joined: December 18, 2003
 And it is almost a certainty that tubes will not get lower in price nor more available with the passage of time, so acquiring spares now as you can aford them makes sence (& they can store under your bed as easily as in someones' warehouse). Because the tubes I use are no longer produced, I've already sufficinent replacements to last my heirs' lifetime (& purchased them while relatively inexpensive). I do not pay extra for matching as such parameters alter during use & most amplifiers submit tubes to higher voltages than used in most testers; my circuts share bias via channel pairs. Out of those dozens of tubes I have, there are perhaps two that will not pair up = cheaper than the cost of matching all those tubes.

Buy many, buy often. You'll never have the problem, posted on October 31, 2009 at 12:38:35
Frihed89
Audiophile

Posts: 8445
Location: Copenhagen
Joined: March 21, 2005
 I end up selling or giving away tubes I have tried, but don't really like. I just got rid of my EL34, KT77s, 6CA7s, but still have a lot of 6550s, 6L6s and KT66s. Nothing like Mike, though.
"What did the Romans ever do for us?"

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