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In-rush Switch Box for McIntosh 240: Necessary?

MrPoetry

MrPoetry

New Member
About 30 years ago I had a "Guy" who fixed my MC240, and he built a switch box for the amp (see below pics). Turn on righthand switch: both outlets received power. Once the 150W bulb became fully bright, turn on left switch: bulb turned off, all power to MC240. I took his word that this was good for the amp, and it gave me a switch for the amp which itself has none.

Recently the switch broke internally. I bought a replacement light switch and wired it exactly the same way the old switch had been wired (which is all I know how to do with wiring). The box now doesn't work properly: regardless of switch positions, power is always on for right outlet and always off for left outlet -- i.e. in below photos, which show all three switch combinations, the MC240 is on and the bulb off.

My question is not how to fix this, but rather, should I bother?

I want a switch for the amp. If some kind of in-rush protection is good for the amp and/or tubes, I want that, too. But would the amp & tubes be just as happy with a power strip or some other kind of switch? If so, recommendations welcome. If not, I can ask my electrician to fix the box so it works as it used to. Third possibility: amp does need some on/off protection, but not this kind of set up, in which case, recommendations needed (I myself can't build or mod anything that won't short out).

Here is how the box worked for 30 years:

20240121_145452.jpg
Both switches are off. Both bulb and amp should be off, but amp is on.

20240121_145501.jpg
Right switch is on. Both bulb and amp should be on. Amp is, bulb not.

20240121_145512.jpg
Left and right switch are on. Bulb should be off, amp on. Analogous to a clock that is correct twice a day, the box in this picture is working as it should: bulb off, amp on.
 
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It looks like a dim bulb tester with a shunt ( a switch that bypasses the bulb). IMO while its not a terrible idea, its really not necessary. I suspect most people running 240s and/or 30s or 40s are running them without issues without one. Its more of a test tool than a protective device. kind of the answer to a problem you don't have.
 
AFAIK, all MC240s have an NTC thermistor in series with the AC power input, which acts as an inrush limiter. I don't think it's necessary to also have inrush limiting in an external power switch.
 
To me, that just looks like a regular dim bulb tester for limiting current. These things are just not really necessary for full time operation unless the amp is on the bench for something not working properly.

You probably should get away from using the dim bulb tester altogether as it is most likely limiting its current capabilitiy and not giving you your full rated watts at full volume. McIntosh has always been over engineered for best performance and will likely sound way better if you plugged it straight into the wall.

I know some people who own some 240's and 275's who have owned them for years with absolutely no troubles being plugged straight into the wall.
 
Look closely at the original switch and see if there is a jumper on the side that has been removed. A lot of those dual switches have a jumper on the "hot" side so you can feed one wire in and supply power to both switches. The outputs will be separate. If this is wired like I suspect, it probably needs the jumper pulled in order for the lamp to do it's thing.

With a bypass switch its not running as a DBT, its just being used as a soft-start. It won't limit power if the bypass switch is engaged and the bulb isn't lit.
 
I was thinking one switch runs through lamp and other switch bypasses lamp. My thought was let heaters warm before applying full b+.
Again if it functions properly (the 240) not necessary.
 
When the new switch was wired in, by some chance was it physically installed inverted (UPSIDE DOWN) so that when flipped in the original position, it`s acting in a manner opposite of intention ?

Most wall switches usually have a molded notation on the toggle knob somewhere indicating the switches on/off`s physical flipped orientation position !
Just a simple thought, for FWIW, and easily checked and corrected.
 
Thank you, all!

Given consensus that external in-rush protection isn't necessary, I've decided to try this combo for adding a power switch to the MC240:

- Woods 14650006-6 Shockshield White GFCI Plug with Surge Protection at the wall outlet (which is a dedicated circuit), to prevent short cycling; plus
- Tripp-Lite Industrial Power Strip (w/o surge protection, AFAIK) plugged into the Shockshield. The Shockshield does seem to have a manual breaker on it, but I want the 6' corded power strip, because the outlet is hard to reach, and I'm not as flexible as I used to be.

If this combo seems like a bad idea, don't hesitate to shout "Wait! Stop! Don't!"
 
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