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Re: MC275 tube troubles...

Posted by Jim McShane (D) on November 24, 2006 at 08:50:52

In Reply to: MC275 tube troubles... posted by rjlpinto@gmail.com on November 24, 2006 at 07:31:22:

"- in the case of replacement, can I buy 3 separate tubes? Any of them must be matched with another?"

You can buy 3 separate 12AX7s, they do not not to be electrically matched.

"- in the case of the fault of any of the 12AT7, same question."

And the same answer! ;-)

You may want to request 12AT7 tubes with good balance between the sections of the individual tube, but they do not need to match each other.

"- I have read somewhere that we should re-tube beginning with the 12AX7, then the 12AT7 and at the end, the 6550/KT88. Why?"

I don't agree. The power tubes (6550/KT88) do not have as long a life as the small tubes. A very loose rule of thumb is two sets of power tubes to 1 set of small tubes.

"- When I need to replace the power tubes, do I have to buy a matching quad??"

In your case yes. Some amps do not require them but in yours I definitely would use an electrically matched quad.

If you could tell us more about why you suspect a 12AX7 we could be more help I think. Not that it's bad to have a spare tube set (a lot of my customers keep a complete spare set on hand), but you may need less.

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