Cold biased tubes for Matchless?

[puddinstone]

I was told that for my matchless I should find a matched quad that is "cold" so they would last a bit longer. I've had some tubes last for a very short time...I was told this was because they were matched "hot".

What should type of reading should I ask for or look for when finding a quad?

Thanks!

[TopBooster]

Doesn't the amp have a bias pot??

If it doesn't (like those darn Mesas), you could specify a set of tubes with higher current draw ratings. Places like www.thetubestore.com (http://www.thetubestore.com) specialize in selling tubes using this method. He calls it the "Perfect Pair" system. Just tell him what amp you have, and ask for the set that will yield the most headroom, while not causing the amp to become too cold. Of course, it may take a few sets for you to get that tone / reliability balance just right...

EDIT - OK, this is a cathode-biased AC30-ish amp, isn't it? Should've known with the _C-30 model number. :jo Yeah, just go higher on the current draw ratings...

[Old Tele man]

...general "rule-of-thumb" for Class-AB1 push-pull output tubes: the closer they're biased to 50% of rated plate dissipation (Class-B cutoff condition with "crossover" distortion guaranteed!) the "colder" they'll sound; conversely, the closer they're biased to 70% of rated plate dissipation (the maximum "safe" operating condition) the "warmer" they'll sound.

[TheAmpNerd]

...general "rule-of-thumb" for Class-AB1 push-pull output tubes: the closer they're biased to 50% of rated plate dissipation (Class-B cutoff condition with "crossover" distortion guaranteed!) the "colder" they'll sound; conversely, the closer they're biased to 70% of rated plate dissipation (the maximum "safe" operating condition) the "warmer" they'll sound.
OTM,

These amps are biased so hot, like AC30s, they ooooze
warmth, and will eat EL84s and the like in short order.

You'll know right away when the tubes start
running away because your tone goes down the toilet.

I have managed to save some great NOS tubes
from melting down though...just in the nick of time too.

Puddin...how long did your last set last?

[puddinstone]

Pullin' this one up...

I had a set of NOS start to go in a couple of weeks. I don't know if they were bad tubes or what....

What kind of numbers should I be looking for?

I've got a cold set of tubes that are label as 11 and that's it. (from KCA) but I see other people use 2 different numbers.

I've seen a 27 and something like 8.6 on a set of the reissue mullard's.

What do I look for/ask for?

[TopBooster]

Pullin' this one up...

I had a set of NOS start to go in a couple of weeks. I don't know if they were bad tubes or what....

What kind of numbers should I be looking for?

I've got a cold set of tubes that are label as 11 and that's it. (from KCA) but I see other people use 2 different numbers.

I've seen a 27 and something like 8.6 on a set of the reissue mullard's.

What do I look for/ask for?

Not sure what these numbers are referring to exactly, since everyone has a different test setup for their tubes, but, when speaking of anode current draw on a particular test setup, you're going to look for the higher numbers in that department... And if those tubes still die early, you should raise your cathode resistor value as John said. It sounds like this thing is simply biased too hot, even for NOS.

[sickboy79]

Pullin' this one up...

I had a set of NOS start to go in a couple of weeks. I don't know if they were bad tubes or what....

What kind of numbers should I be looking for?

I've got a cold set of tubes that are label as 11 and that's it. (from KCA) but I see other people use 2 different numbers.

I've seen a 27 and something like 8.6 on a set of the reissue mullard's.

What do I look for/ask for?

Did Mike recommend that rating? He's got some great info about cathode biased EL84 amps on his site. I would assume you need a colder set.

[MrChet]

The best solution, IMO, is to adjust the cathode resistor value up. As long as you're between 50% - 70% dissipation your tube life will improve w/o "cold" sounding tone. My experience w/ cathode biased amps is that 55% to 60% dissipation give me good tone and good tube life.