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hi all,
i think it's probably time for new power tunes for my McIntosh MC60 monoblocks.
do all new 6550/KT88's have about the same output? or do some brands have more output than others? i'm thinking new russian tubes.
i bought new (at the time) Svetlana Winged C 6550's around 2004. in the last year or so, every once in a while, i'll get am arc or flash upon start-up. didn't seem to affect performance. i figured it was because i was messing around and didn't have the amps off long enough for the caps to dissipate their charge before turning them back on.
a few weeks ago, i had the stereo on for a while... and i heard a muted pop from the speakers. nothing super loud. i wondered if one of the power tubes arced again. since then, there is no obvious distortion, but the amps just don't seem to have the same amount of juice they used to. if you push them too much, they seem to strain.
i know when i had the amps gone through a few years ago, the tech said the amps reached their manufacturer's distortion limit at 45wpc... BUT when he tried is good testing vintage GE 6550s, the amps made it to 55wpc.
i'm assuming output falls off as tubes age, right?
anywho, i just looked on ebay. are winged C's collectible now or something? they are EXPENSIVE! are they that much better than the current stock of svetlana 6550's? what other tubes would you suggest along those lines?
Regards,
Robby
Follow Ups:
They are very balanced and they measure the most power and lowest distortion of all the reliable tubes.Get them from Jim because they are well matched.
Honest amplification is better than excessive 2nd order distortion anytime.
Contact the guy who just responded to you, Jim McShane.
Winged C/SED production is done - no more are being made so the supply is very small and the price is very high.
I've helped a bunch of people retube Macs with the KT88 Genalex reissues. They work VERY well, I highly recommend them, and they'll be much less expensive than the winged Cs.
Also, for you to notice a difference in output power the tubes would have to be quite weak. 10 watts difference is barely or not audible at all in most circumstances to most people. But the repeated arcing IS a concern, and since the tubes are about 10 years old it's time for a change!!
yeah, i've been told i wouldn't hear the 10 watts.
question for you though... i thought MC60's put out close to 65-70wpc... is 45wpc or 55wpc cause for concern?
my tech (arden allen) replaced the usual audio couplers and installed new cans. he DID NOT "over-cap" the power supply. still the stock uF. would adding more capacitance beef up output or not really?
i also believe he gave maximum output based on McIntosh's stated distortion limits. so, perhaps when people say MC60s put out close to 70wpc, they are pushing them past the company's stated distortion figures?
i'm running the amps with Yamaha NS-1000M monitors and a powered REL Q100 sub. been the same core system for about 7 years. so i have a pretty good feeling about what the system can do. and it USUALLY rocks like there's no tomorrow. it seems like it's hitting a "rev limiter" now ;-)
Regards,
Robby
Robby,
His measurement may have been made under more stringent conditions than the factory spec. Or the tubes themselves were at fault. The factory rating is 60 watts, it's possible others weren't so careful about how they measured the power out. There are a lot of ways to look at the output and find it is higher - drive the amp to higher distortion levels, restrict the power measurement to a mid band frequency like 1KHz, or measure just one channel at a time, etc. From the sound of it, I think your tech is closer than the other measurements you're aware of.
Using larger amounts of capacitance has relatively small effects on RMS (continuous) power, but it does improve the amp's peak power performance which I maintain is every bit as or even more important than the RMS power. For instance, a stock Citation II has a peak power rating of 130 watts/channel. After Don or I get done completely redoing one we see in excess of 150 watts per channel peak power, probably about 180 or so is the actual. So there's where it comes into play.
The KT88 Genalex produce full output in the Deuce as long as they are healthy and the driver tubes are also in good shape.
So get a quad of Genalex KT88s, be sure the driver tubes are healthy - and enjoy that FINE amp!!
awesome info Jim!
the driver tubes were NOS american tubes from a few years ago. they sounded better to my ears than my decent testing smooth plate telefunkens.
just as my then new CED 6550's sounded better than my good testing tungsol 6550's.
the rectifiers were good testers from a friend. they are different than the ones which were in the amps when they were gone through.
i'm assuming as rectifiers age, power drops too?
would you buy new russian 5U4GB's or stick with good testing american ones?
Robby
What Eli Duttman said is good advice - the EH are quite good, the GEs are a very good tube and a bargain compared to RCA.
Some rectifiers drop more voltage than others. More voltage drop = lower B+ (supply) voltage = less power.
The current production EH 5U4GB is a good tube. All other 5U4 variants made in China and Russia are junk.
JMO, look for NOS GE 5U4GB stock priced competetively with current production EH tubes. NOS RCA and TungSol 5U4GB stock may be somewhat better, but the price premium is (IMO) too high.
Eli D.
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