Re: McIntosh MC-30: Detailed 6L6GC, 12BH7, and 12AX7 questions...

Posted by jdiamantis (A) on September 28, 2006 at 12:56:54

In Reply to: McIntosh MC-30: Detailed 6L6GC, 12BH7, and 12AX7 questions... posted by Audible Nectar on September 26, 2006 at 06:15:26:

I own/refurbished/use a pair of MC-30's. RE; the remark about harshness - properly set up, an MC-30 is anything but harsh. I'm sure the tube rectifier has something to do with this. The MC240 is a different beast, sounds different than the MC-30, and benefits from some modification.

When changing components, pay special attention to the 12BH7 plate resistors. In most McIntosh amps I've serviced, these resistors are bad. Relace them with at least 3 watt units, if not 5 watters.

The bias circuit uses a selenium diode. These do go bad with time, and if they fail, emit toxic fumes. Replace with a power silicon type 1n4003 or better. When doing this, you must add a dropping resistor to achieve the correct bias. You could add a series pot here along with a fixed r. You can start with a value between 3.3kohm and 4.7kohm 1/2 watt is fine. Adjust as needed.

If you are adding capacitance to the power supply, do not add it directly after the rectifier tube. Add value to the cap after the 1st series power resistor that feeds the output tubes.

I played around and modded the MC-30's, but finally rebuilt them stock and never looked back. Properly refurbished, and voiced with tubes you like, they sound great, and have a great midrange, solid low end, and clear highs.

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Follow Ups Full Thread

Topic - McIntosh MC-30: Detailed 6L6GC, 12BH7, and 12AX7 questions... - Audible Nectar 06:15:26 09/26/06 (16)

Re: McIntosh MC-30: Detailed 6L6GC, 12BH7, and 12AX7 questions... - jdiamantis 12:56:54 09/28/06 (0)

seriously, think about a CCS on each splitter-driver - Timbo in Oz 15:33:57 09/27/06 (4)

Re: seriously, think about a CCS on each splitter-driver - Zung 11:49:25 09/28/06 (3)

yeah, you can get away with a good deal less NFB with A CCS on small signal tubes in diff'l - more so with - Timbo in Oz 19:56:07 09/30/06 (2)

Should I bother to do the calculations, on the triode connected amp? - Timbo in Oz 14:54:35 10/04/06 (0)

Triode-connecting a Mac? - Zung 08:37:57 10/01/06 (0)

Re: McIntosh MC-30: Detailed 6L6GC, 12BH7, and 12AX7 questions... - Zung 14:40:27 09/26/06 (4)

Re: Fixed bias - Jim Womble 18:00:24 09/26/06 (1)

Re: Fixed bias - Zung 12:06:36 09/27/06 (0)

Re: McIntosh MC-30: Detailed 6L6GC, 12BH7, and 12AX7 questions... - Audible Nectar 15:37:50 09/26/06 (1)

Re: McIntosh MC-30: Detailed 6L6GC, 12BH7, and 12AX7 questions... - Zung 12:14:04 09/27/06 (0)

Re: McIntosh MC-30: Detailed 6L6GC, 12BH7, and 12AX7 questions... - dubai2000 11:52:13 09/26/06 (0)

There's not much to these gems.... - doodlebug 08:40:33 09/26/06 (3)

Re: There's not much to these gems.... - Audible Nectar 12:36:32 09/26/06 (2)

Finally!!! - Sector-7G 13:48:00 09/26/06 (0)

Re: There's not much to these gems.... - Jim McShane 12:44:30 09/26/06 (0)

Follow Ups

Re: McIntosh MC-30: Detailed 6L6GC, 12BH7, and 12AX7 questions... - jdiamantis 12:56:54 09/28/06 (0)

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