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In Reply to: RE: Late Model MC240 Resistance Tables posted by HouseOfToine on March 08, 2015 at 05:55:34
Do you have a variac? Don't worry about the resistors because they amp obviously worked before.Bring it slow and insert your amp meter in place of the fuse and watch that it doesn't go crazy as you crank it up.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
Follow Ups:
If I can't find the revised tables I'm going to go through it once more to make sure everything is as it should be, then I'll power it up and watch current and take voltage readings at the tubes. Thanks
One thing I want to tell you tho is to take out the Modafarri updates because I can tell you that Mcintosh never approved them and with the resistor changes in the phase inverter,the mods raised measurable distortion.I'm glad to hear you run Martin Logans..I have the CLXs but I still have my Monolith 2s as well but always run the CLXs on a pair of Citation 2s or the Mac amps and both give wonderful results. I used to chuckle at people that said you have to run Martin Logans on a sand amp..Nothing could be further from the truth but McShane's power supply upgrades for the Macs and Citations are the ticket to really waking those amps up because you dramatically increase the energy in the power supply while lowering ripple current and impedance by quite a bit..
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
Holy Crap! You hit the nail on the head!
It never occurred to me that the resistors had been replaced with different values. I never gave them a thought assuming they were just modern updates. 33K instead of 12K, 5.1k in place of 2.7k, 27k instead of 18k. It goes on. Take a look.
Exactly.
That circuit is designed like no other and Frank Mcintosh and Stu Hegeman were very particular in their execution of nested loop feedback as well as running the tubes in the most linear portion of the phase inverter and the voltage amp..Very critical for the sonic signature.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
Looks like I'll be rebuilding this one completely.
It looks like they did neat work,but put the wrong value resistors in.
As Mike pointed out, they were done as a specific mod and it was good work. I'll be bringing it back to the original circuit with equally good soldering skills!
Mike rebuilt my Mc240 and it is beyond improved and wonderful sounding.He is a great guy to deal with and really knows his tube electronics.
So I swapped out the dozen hi value resistors for stock values and all of the readings fell into spec +/- 10%. The carbon comps that remain will be replaced with CF & MF 1% and it should be good to go.
It's Alive! All is well in MC240 land. Voltages are within 10%. A full resistor swap should have it right on spec. It even sounds good!
Thanks for the help.
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