MR78 mystery

[Vintage Pete]

Originally Posted by altbrewer

Well, son is married, visiting family have gone home and life is back to a semblance of normal, so I finally got back to this project. As it turns out, whoever worked on it before had the diffuser in backwards:

Attachment 11464

You can see it is flipped left to right, with the white mask for the markings around the volume control on the left in this picture, which is the right from the front (volume control is on the right on frontal view)

Here is the way the diffuser was oriented against the bulbs. The poorly drawn red circles show where bulbs and holes for the bulbs do not line up:

Attachment 11465

And flipping the diffuser over makes the bulbs and holes line up:

Attachment 11466

I couldn't include the last pic in this post so will show the final result in the next. I see I still haven't got the hang of placing full size images in the text of a post.

Wow...you had mentioned the diffuser in place but didn't mention anything amiss with its orientation. It seems pretty obvious that someone had the unit apart and did not reassemble it correctly. That would definitely mess up the light diffusion...I can't imagine this having been done at the factory.

Glad you got it solved, between that and removing the resistor, you should be in good shape!


Pete

[Vintage Pete]

I see from your last photo that it looks perfect. How did you re-attach the diffuser?

Pete

[altbrewer]

The diffuser has a screw at each end that attaches it to the faceplate bracket. They should be visible in the first photo. It is also held in place by the tape mask at the top of the diffuser.

[Vintage Pete]

That's right...I forgot about the two screws. The tape mask should also have some polyurethane foam on it that acts as a light seal. Over time, this can deteriorate and can be replaced. There are also one of these at each end of the dial glass.

In case you are interested, there are a couple of threads in which I chronicled a complete cleaning of my MR78.

Here is the main cleaning thread:

http://audioaficionado.org/showthrea...=mr78+cleaning




And here is the replacement of the foam tape light seals:

http://audioaficionado.org/showthrea...=mr78+cleaning


In this thread, I also discuss the resistor removal. (I hadn't gotten my close up photos perfected at this point-I'm much better at it now).



Pete

[jdandy]

Mike.......She's looking good now. Great job.

[longgone]

Is there a little switch on top of the tuner that brightens or dims the lettered lights?

[Vintage Pete]

Originally Posted by longgone

Is there a little switch on top of the tuner that brightens or dims the lettered lights?

The switch on top only dims the dial scale and tuning/signal strength meter lights-not the lettering across the lower front panel.


Pete

[longgone]

Hi Pete, my 78 is in a cabinet and I wasn't certain if I was thinking about that switch being on the 78 or maybe even another Mac unit (I have a C27 and a 2205). Pretty cool idea (the switch)? It's been a while since I played with that switch and since you mention it's function I remember as you described. You have a beautiful MR78. Nice work. I super like mine! I also have some 1.2's and does that 78 ever sound nice! Hard to turn it off ... losing sleep ... heh heh.

[Vintage Pete]

Originally Posted by longgone

Hi Pete, my 78 is in a cabinet and I wasn't certain if I was thinking about that switch being on the 78 or maybe even another Mac unit (I have a C27 and a 2205). Pretty cool idea (the switch)? It's been a while since I played with that switch and since you mention it's function I remember as you described. You have a beautiful MR78. Nice work. I super like mine! I also have some 1.2's and does that 78 ever sound nice! Hard to turn it off ... losing sleep ... heh heh.

Yes, the switch is a cool idea, though I always leave it on the "bright" setting. I also have an MC2205 in my Florida room with a C32 and MR77. Love that vintage McIntosh gear!

Pete