Tube testing the McIntosh MC2301's

jdandy

jdandy

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It's been just over a year since I last tested the 16 Gold Lion KT88 tubes and the four Siemens ECC801S (12AT7) driver tubes in my two McIntosh MC2301 amplifiers. I maintain a spreadsheet on each tube in each amplifier. This allows me to track the power tubes' plate current and transconductance, comparing the current numbers to those of new tubes and against what is considered the low end of useful life. The Gold Lion tubes have 2,268 hours on them as of this evening. I was pleased to see the plate current and transconductance numbers are still very close to what I measured last year. All 16 KT88's displayed a minimum of 60% useful life remaining with plate current and transconductance numbers continuing to be relatively close matched.

Each MC2301 uses eight KT88 power tubes and two 12AT7 driver tubes. Testing the four Siemens ECC801S tubes revealed almost no change in their triode gain numbers, triode matching, or noise levels. I expect the Siemens tubes to last 10,000 hours, perhaps even longer.

With the tubes removed I had the opportunity to wipe the dust from the chassis of each amplifier with a microfiber cloth before reinserting each tube back in its respective porcelain socket and replacing the tube cages. At the same time I unplugged and reinserted the balanced cables at the amplifier input terminals and on the rear of the C1000P preamplifier. Fresh contact never hurts anything. I did the same with the speaker terminals on the amps and the SF Amati Anniversario speakers.

With my annual preventative maintenance behind me, I am now enjoying the fruits of my labor. The studio system sounds sublime.
 
Here are my two tube testers in action.


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Hi Dan,

Wonderful update on testing and tube management. Looks like those wonderful MC2301's are pretty easy on tubes.
 
joeinid said:
Hi Dan,

Wonderful update on testing and tube management. Looks like those wonderful MC2301's are pretty easy on tubes.
Click to expand...

Joe.......The McIntosh MC2301 power amplifiers are easy on output tubes, either KT88 or 6550 tubes. The MC2301 amplifier is fully balanced from input to speaker output. There are two identical power amplifier channels on the chassis operating in balanced configuration. Each amplifier supplies one half of the 300 watts output. The two outputs are combined in the output transformer to deliver the full 300 watts output. The four output tubes in each half of an MC2301 amplifier deliver signal to the output transformer through two primary windings in the patented McIntosh unity coupled output circuit, one for the tube plates and one for the tube cathodes. Taking signals from both the cathode and the plate of each tube is unique to McIntosh amplifiers with their bifilar wound transformer and allows the power tubes to operate more efficiently without the need to push the tubes to their maximum while still achieving full rated output. This extends tube life substantially compared to many other manufacturer's designs. Where other manufacturers struggle to reach 2,500 hours on their output tubes, McIntosh tube amplifiers often reach 6,000 hours with the same tubes. That represents a savings for me since it costs $960.00 to re-tube a pair of MC2301's with KT88's at current prices. If I get two times or better service than everyone else's tube life, that represents a big savings.
 
Will the 2301 accomodate KT-120s? I ask because after having auditioned a variety of KT-88s (not in Mac amps by the way), I haven't found one I actually liked.

Thanks.
 
kevinkwann.......The MC2301 amplifier does not use KT120 power tubes, only KT88 or 6550 tubes. I don't know which amplifiers you have auditioned with KT88's but you owe it to yourself to audition the MC2301's. They are exceptional tube power amplifiers.
 
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