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McIntosh MC-240 restoration.

Very nice work.Are you going to leave the original power supply diodes?Jim McShane told me that modern diodes are faster and have less noise.If you are going to order clamps from him,you may want to ask him about those diodes.I think that the Mc240 is a nice sounding amp,and really like mine.The only problem is that if your preamp,phono stage and speakers are not on par with the Mc240,you will find the need to upgrade...I just bought a nice tube phono stage.
Dave
 
:tresbon: This thread has turned into my own personal sticky. Please don't ever delete or dilute this wonderful topic.

Thank you,


Steve
 
drillher said:
Very nice work.Are you going to leave the original power supply diodes?Jim McShane told me that modern diodes are faster and have less noise.If you are going to order clamps from him,you may want to ask him about those diodes.I think that the Mc240 is a nice sounding amp,and really like mine.The only problem is that if your preamp,phono stage and speakers are not on par with the Mc240,you will find the need to upgrade...I just bought a nice tube phono stage.
Dave
Click to expand...

what diodes did you use to replace those silicon diodes?

i have a few kinds that'll exceed the current spec like 1n5408 and such...3a 1000v.

PakProtector said:
hey-Hey!!!,
It is just the heater connections. If you look at the socket you'll see where pins 4&5 are tied together and the other side is fed to pin 9. You need to apply the 6.3V across 4 and 5 for the 6CG7. Since pin 9 is not used on the 6CG7 what I've done is separate pin 4 and tie it to pin 9 and reconnect from pin 5 to the following 12AX7 stage. Solid core is useful here 'cause it will keep its shape once bent.
cheers,
Douglas
Click to expand...

sounds like an easy enough mod.
 
I used 1N4007s for both the power supply and the bias circuit. Jim's diodes, IIRC, are the hexfred types or close to them. They're surprisingly inexpensive from Jim so pick up a handful when you make an order.

Cheers,

David
 
Jim was the source for my diodes,so I'm sure that if you email him he will advise you well as David is doing here.
 
hey-Hey!!!,
These diodes should be the best you can get; unfortunately tubes won't be an option. SiC Schottky are worth the extra coin; they have no reverse recovery issues as even the best of the P-N junction ones do. For the 240, 5A/600V is a conservative choice, run well within its ratings.
cheers,
Douglas
 
i can't locate clamps in my garage....i had a few dozen that's hidden somewhere. i gotta clean up the area and organize. :D

anyways, i did connect the new filter caps and the amp powered on without any problems. everything measure close to spec.

when sound tested, there are particular layer of noticeable distortion at higher volume. i suspect the black beauties....:scratch2:
it could be the rca connectors or the pots & stereo/mono/twin selector.....OR even dirty tube sockets. which tells me that the amp is far from completion.

i'm gonna replace them and see if that was the case.

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PakProtector said:
hey-Hey!!!,
These diodes should be the best you can get; unfortunately tubes won't be an option. SiC Schottky are worth the extra coin; they have no reverse recovery issues as even the best of the P-N junction ones do. For the 240, 5A/600V is a conservative choice, run well within its ratings.
cheers,
Douglas
Click to expand...

i need to place a digikey order this week. i should order some of those you suggested. is this what you're talking about? i should order some 2A ones for other applications, too. 5A 1200v ones are indeed pricey....$5.29/piece.
http://www.infineon.com/dgdl/IDH05S...b281a&fileId=db3a3043284aacd80128b04ff3e05608
 
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On the replacement caps, do you have the correct voltages along the high voltage divider? That's first.

Next, are all the operating voltages up and down the tube string in spec? I suspect not and that leaking coupling caps are your problem. I'd replace them all and retest.

Lastly, the bias voltage needs to be confirm using the variac technique in the Hints and Kinks sticky.

You're moving along, though.

Cheers,

David
 
dshoaf said:
I suspect not and that leaking coupling caps are your problem. I'd replace them all and retest.
David
Click to expand...

that was it!

the problem solved rather quickly and easily.
as suspected, changed out the black beauties, and the amp opens up in a BIG way!

sound stage and separation is simply amazing. no distortions. i'm sure not all of the BB's were bad, but i guess one of them was that few went bad. can't say what i think of them though.

i can only hook it up to my crappy work speakers and use itune as a source, but i can tell right away something special about the sound.

so the BB goes to the "taken out crap" pile.....:D



been listening for last hour or so...can barely notice warmth of power transformer. i love it. deep and tight bass. can't wait until i take it home and hook it up to real speakers.....

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golana said:
Ghetto-tastic!:thmbsp:
Click to expand...

lol.
right now playing through ghetto speakers put together with jensen horns and crappy no name woofers in coral cabinets. playing some velvet underground and sam prekop, and i've never heard these crappy speakers sound so good....
 
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drillher said:
What did you replace the black beauties with?So much for them being good most of the time.
Click to expand...

i know...

all of them BB's DO test 0.25 - 0.27uf, but some of 'em are probably leaky.

i just used basic mallory caps i had at work to test (and no noise or distortion whatsoever!), but planning to use either russian pio, or auricap.

i'll probably have to run the amp for at least a few days to break-in all the new parts, but while listening to it as is, one thing is for sure: sound stage, separation, and depth is unlike most other amps i've heard.

another noticeable thing is the bass reproduction. very smooth, deep and tight. those huge OPT at work :thmbsp:

some recordings sound better than others, and the funny thing is, what sounded good before (with eico hf-87 & SAE 2600) sounds so so, and what sounded so so with above amps sounds great with MC240! i guess the amp is revealing different areas of each recording.

drillher, you should try your multicaps in place of those BB's. if you decide to keep the BB and not switch 'em with multicaps, let me know. i might be interested in them.
 
it's hooked up to audio research tube preamp and econowave/bozak right now. i'm gonna get familiar with the sound for a few days and then replace the 0.22uf caps and try it again, and then use different speakers and passive attenuator.

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Crap-tastic, congrats! :D Meaning, some folks might think it "looks" like crap, but if it sounds fantastic, who cares. :smoke:
 
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