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In Reply to: RE: McINTOSH MC-30 & FISHER 90-C REBUILD by MIKE SAMRA posted by ssimon@wideopenwest.com on February 23, 2016 at 18:45:53
On the 50 watts I was getting,that was with a 5AR4 rect and the AC on the 125vac tap with 6L6gcs.The 6P3Se tubes made like 3 less watts is all but their sonics are superb.
A friend you get for nothing,an enemy has to be bought
Follow Ups:
I thought I was going to read how the 12AU7 got ditched in favour of the 6CG7...:) The PS stuff mirrors what got done to my W6m's. Added a Hammond choke, and improved the capacitance. Those amps will next get some Russian POI couplers next time I have the hoods up( fortunately, they're 2-stage, and I'll only have to cram 2-each under there).
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
The 50-50 split between cathode and plate loading of the McIntosh unity-coupled power stage delivers quite enough NFB. There is of course positive FB delivered to the 12BH7 stage; this bit should go away, and with it the loop of global NFB.
While you're at it, the phase splitter stage can benefit from a proper CCS tail load, and repair of the deliberately imbalanced plate resistors( put there to deal with the imperfect tail load.
After all this you'll likely discover an overabundance of gain still exists. Change from a 12AX7 input tube to a 12AY7( the cathode R will need adjusted ), will be useful.
The amp will be more stable, and thanks to removal of the gNFB, and local PFB it will sound better too.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I asked him about that and he wanted to leave that and maybe run a 12BH7.I run the 6CG7 in most of my Macs and I totally agree but I'm also making up adapters where they can run a 6CG7 in place of the 12AU7.Your setup sounded incredible and the bass was some of the best if not the best I have ever heard..You had just moved in the house and your room wasn't even done yet and I couldn't get over those base horns and then the RCA compression drivers on the horns for mids driven with your 4E27 amps..
A friend you get for nothing,an enemy has to be bought
Fair enough...:) I would have been worried if you didn't offer...LOL
In addition to the set up being new when you heard it, you were also slightly sleep deprived thanks to the AK Fest going on that weekend.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Congratulations on your beautiful vintage system.Mike is very talented in his ability to make tube amps better than they were new while not altering them in ways that compromises collectability.Mike rebuilt a Mc240 for me which is dynamite,but I needed more power to drive Magnepan 1.7's.He recently worked his magic on a Mc275 for me that is truly magnificent! I need to sell the Mc240,but I can tell you that I will keep that Mc275 until my ears are too old to appreciate it!
Dave
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