Sub Types Of Mc240?

drillher

Super Member
Jim McShane puts together two different resistor sets for the Mc240.I didn't know that there were two variants.How do I tell which type I have?
 
I've had half a dozen or so over the years. I had no idea there was a "mid" production unit - I've certainly not seen one. I have had one of the early units.

Learn something every day. Great stuff there 62caddy.
 
I'm curious, does he have a similar set of pages for the versions of MC40 ? I tried searching his site, but cannot find it (nor can I navigate to the link you provided below without just clicking on what you provided).

 
Thanks.I have a later model with a single socket preamp input.I plan to replace the four black beauties,which were the only original coupling caps that I left in.I plan to also replace the resistors with the kit that Jim McShane puts together.
 
I've had half a dozen or so over the years. I had no idea there was a "mid" production unit - I've certainly not seen one. I have had one of the early units.

Learn something every day. Great stuff there 62caddy.

Berners site is very informative! :)

I'm curious, does he have a similar set of pages for the versions of MC40 ? I tried searching his site, but cannot find it (nor can I navigate to the link you provided below without just clicking on what you provided).

This was all I was able to find on the MC 40.

It appears there may only be one version.

http://mcc.berners.ch/power-amplifiers/MC40.pdf
 
This was all I was able to find on the MC 40.

It appears there may only be one version.

http://mcc.berners.ch/power-amplifiers/MC40.pdf
Actually, I know of two different versions of the basic circuit, and two different versions of the power transformer - giving rise to (at least) three different versions of the amp (since these changes occur at two different serial numbers). I have no idea if these correspond to the three versions of the MC240 that he shows, since there are no schematics shown for those; I think not though, since all three versions of the MC240 seem to have the 117/125VAC line voltage switch.

In older MC40s, the power transformer has primary windings for 117VAC and 125VAC and a switch to select between the two. In the newer one, there is no switch, and a different power transformer that can be wired alternatively for use in 240VAC versions. In one, the power supply choke is integrated into the power transformer, and in the other it is a separate component.

In one variation of the circuit, the power supply provides different voltages to the circuit B+ and the output transformer center tap. In the other, those voltages are combined, with some resistors in the circuit adjusted. There are also some minor variations in capacitors in the signal board.
 
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Not all late version MC 240s have the voltage switch either...
 

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In the version with one octal socket is set up for 70V outputs at the socket and can not power a preamp.
 
As an addendum to this thread:

Terry just informed me that the MC 240 I have (without voltage selector switch) is rare European version - designed for simpler conversion to 240 VAC.

I always wondered why mine doesn't have the voltage selector...
 
lol

She's not for sale - just too nice.

But I'd give Kevo first crack if it comes to pass...:D
 
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