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Old 13th November 2004, 01:21 PM   #1
markp is offline markp  United States
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Default MC-30 rebuild, any ideas?

I was given a McIntosh MC-30 amp that was gutted of all passive parts by someone many years ago, so I have the chassis and transformers. Any ideas on what I should make out of them or should I just remake the MC-30 as it was? Please feel free to be creative!
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Old 13th November 2004, 02:34 PM   #2
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I would rebuild MC-30 as it was!
It's not a common amp!The OPTs are for unity coupled configuration.Maybe they'll work as UL,too.But it's very difficult to find these days such kind of OPTs so, it's a nice idea to try unity coupled.
The only thing that I'd search about is to bias it at class AB or A.
And this because MC-30 as I remember is biased in class B.But you must be sure if transformers can handle more current.
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Old 13th November 2004, 03:48 PM   #3
EC8010 is offline EC8010  United Kingdom
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Yes, rebuild it as an MC-30; there was a thread here quite recently that gave a site with full McIntosh diagrams:

http://www.berners.ch/McIntosh/de/Frame_Matrix.htm

I had a quick look and note that the MC30 uses 12AX7 and 12AU7. As you would be starting from scratch, you might want to consider using 6SN7 in place of 12AU7 and 6SL7 in place of 12AX7. The 6SN7 draws more heater current, so you might decide to use a separate heater transformer (always a good thing to split heaters off from rectification).

It all depends on how keen you are. The output transformers are designed for a very specific use, so you don't have any choice there - it's only in the details that you have choice.
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Old 13th November 2004, 04:04 PM   #4
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Or how about using 5751 and 6CG7/6FQ7? They would fit the sockets at least. Is there anything closer to a 6SL7 than the 5751?

Best regards,

Mikkel C. Simonsen
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Old 13th November 2004, 04:39 PM   #5
markp is offline markp  United States
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Quote:
Originally posted by resident
I would rebuild MC-30 as it was!
It's not a common amp!The OPTs are for unity coupled configuration.Maybe they'll work as UL,too.But it's very difficult to find these days such kind of OPTs so, it's a nice idea to try unity coupled.
The only thing that I'd search about is to bias it at class AB or A.
And this because MC-30 as I remember is biased in class B.But you must be sure if transformers can handle more current.
MC-30 it will be! I will look into the bias to make it at least AB, the transformers are battleships and I'm sure can take the extra load.
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Old 14th November 2004, 04:17 PM   #6
anatech is offline anatech  Canada
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Hi Markp,
I've rebuilt many McIntosh amps in the past. I think I have an MC30 schematic I can send you if you need, just pm me.
With modern components, this amp should sound better than it did. First build it as it was designed, then try to increase the bias current to see how it sounds. The phase splitter had matched resistor I think, around 12K. Increase the wattage rating on these over stock. I recall using 2W resistors.
If the cases are rough, have them re-plated. I did some in a semi-gloss brass with black xformer covers. That looked really sharp. My cases were badly rusted so there was no question of retaining the cosmetic value.
-Chris
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Old 15th November 2004, 12:36 AM   #7
markp is offline markp  United States
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Quote:
Originally posted by anatech
Hi Markp,
I've rebuilt many McIntosh amps in the past. I think I have an MC30 schematic I can send you if you need, just pm me.
With modern components, this amp should sound better than it did. First build it as it was designed, then try to increase the bias current to see how it sounds. The phase splitter had matched resistor I think, around 12K. Increase the wattage rating on these over stock. I recall using 2W resistors.
If the cases are rough, have them re-plated. I did some in a semi-gloss brass with black xformer covers. That looked really sharp. My cases were badly rusted so there was no question of retaining the cosmetic value.
-Chris
Thanks for the offer, but luckily I have the schematics. My case looks to be in good shape for being 40 years old! What about going to solid state recifiers, any good? I'm also debating on which output tube to use, both brand and type( vintage 1614s or 6l6GCs or what).
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Old 15th November 2004, 12:39 AM   #8
markp is offline markp  United States
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All my parts for my other amp a MC225 should be here tomorrow so I'll see how that turns out by comparing one channel to the other before I put the new parts on both sides.
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Old 15th November 2004, 01:02 AM   #9
anatech is offline anatech  Canada
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Hi Markp,
Try first with the tube rectifier, that's stock. MC-40 's used solid state rectifiers. The supply will have a smother rectified DC (no HF spikes). For outputs, have been using Electroharmonix lately. I've been pretty happy with these and the cost is much more for something better.
-Chris
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Old 15th November 2004, 02:09 AM   #10
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The MC-30 has very nice output iron...

Depending upon the condition of the chassis you might want to just build one up as it was... it is a pretty nice design. It works well.

I had one on the bench for 20+ years as the bench amp... Have a 50-W2 in that role now. Cooler looking but actually the MC30 works a bit better overall.

They used the 1614 steel cased 6L6 style tube.

And no it won't work as an ultralinear transformer...

You could substitute in almost any tube that ends up with the requisite plate impedance and power level...

Of course having only one of them sort of limits you as to what you can do with it.

If the chassis is in good shape and you have the bottom cover, it has some collectors value that way. Something to consider.

So, I wouldn't gut and drill the original chassis if ur planning on a different input circuit... the Japanese or someone with a rusty chassis would like to own the one you have and will pay for it.

If ur gonna do a new input design or use different tubes, lay it out fresh on a new chassis...

my 2 cents...

_-_-bear
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