MC2205 Love - Part 3

[Gregory]

MC2205 Love - Part 3

This is the third installment of the 2205 amplifier 30 year service, overhaul, or rebuild.. which ever you prefer. Today we will attempt to disassemble the meter chassis assembly and refit it with new foam, blue filter sheet and other materials. Please see the QUESTIONS section near the end of this post to recommend sources for these materials.


Meter Chassis Assembly and Bracket

From Part 1, the meter assembly was removed since it had adhesive residue from the old and deteriorated strips of polyfoam tape. The following is a photo of the meter chassis assembly with adhesive goo.


MC2205 meter chassis assembly with adhesive residue from the original polyfoam tape.


In order to dissolve the adhesive, the lamp housing and meter assembly had to be removed. First the lamp housing was dis-attached, and the three meter fasteners (castle nuts) removed from the black chassis/bracket. Rubber bands were added to keep the plexi-sheet in place. Note the yellow plastic clip with rubber jaws applied to protect the meter ribbon pins.


MC2205 meter meter assembly with lamp housing and Lamp PC board. Rubber bands added to keep plexi-sheet in place.


The adhesive was easily removed with Goo Gone after the chassis was separated from the electronic components. The following is a view of the black meter chassis/bracket looking almost brand new with all screws and hardware scrubbed or replaced with stainless.


Meter chassis/bracket decontaminated and hardware/screws restored or replaced.


Meter Assembly

Now it's time to clean up the outer plexi-sheet which also had crud and foam crumbs on it. The 1/4" foam strips on the lamp housing need to be replaced. It is also an objective to change the blue filter sheet material in between the plexiglass since it's old and warped by heat from the lamps. The following is a view of the plexi-sheet attached to the meters with a VERY tough butyl tape (material not confirmed.)


Closeup of the tape that holds the plexiglass sheets to the meters. This stuff is TOUGH!! You can see foam crumbs along the center.



Meter assembly with plexi-sheet (and foam crumbs) and tough black tape at the base (near meter movements.)


The following is a view of the outer plexi-sheet that can be hinged on the VERY strong tape. The blue filter sheet is sandwiched in between two plexiglass layers and is easily exposed/accessed, however it is stuck to the black tape at the base and will not come out easily. This will be a delicate operation!


Meter assembly with outer plastic sheet raised, exposing the blue filter film which is sandwiched between plexiglass layers.


Lamp Housing

The lamp housing was separated from the meter chassis assembly in order to remove deteriorated foam strips. The two end-brackets with foam tape are riveted to the housing. All four of the rivets are rusted and could be drilled out and replaced, making access to the fiber-board much easier. There is also a center bracket that had form-backed tape on it (not shown, see second photo from top.) The following is a photo of the lamp housing with lamps inserted. Only two of the lamp sockets have developed rust on the teeth. One of the threaded holes (left side, red dot) was stripped, so the two fasteners may have to be replaced with stainless machine screws and nuts.


Lamp housing with lamps inserted. The foam tape at each end is disintegrating.



Top of lamp housing. The fiber-board backing is dry rotted from lamp heat and cracks with the slightest effort to remove it.


Questions

Foam-backed Tape: what type of foam-backed tape should be used to replace the meter to glass interface? Poly-foam or sponge rubber foam?

Filter Film: what are some vendors for replacement blue filter film?

Lamp Housing Backing Paper: in order to dissolve the old foam strip ends, the backing paper will need to be removed from the housing, however it will be destroyed in doing so. What is a good replacement?

Butyl Tape: if in fact that really tough black tape is butyl, is it a good idea to attempt removal of the plexiglass sheets? or is there too high a risk that damage will occur to the fragile 2205 power meters? I also understand they [the meters] aren't available anymore?


Wrap-up

That about wraps up segment one of MC2205 Love - Part 3 dealing with meter assembly rebuild and restoration. The terms poly-sheet and polyglass are used interchangeably in the context of this post. Reassembling the meter chassis is going to be the biggest challenge of the project. With input from other Mc'ers, suitable materials can be found.


MC2205 meters held to the plexiglass with tough black tape (and rubber bands.) One must be VERY careful with these babies!!


Please comment and suggest options and materials to restore the meter assembly and chassis. This is an open discussion and not a how-to or tutorial. If all goes well, and with the help and input from the McIntosh community, this will be a smashing McIntosh amplifier for many years to come.. easily for the rest of one's life!!


-Gregory

McIntosh owner for over thirty years.

[dewickt]

Foam tape, I use open cell foam weather strip, closed cell is a bit to firm, available at Lowes and sometimes Home Depot.
Blue gel can be bought from the factory or Parts Express #244-141 (bright blue).
Backing paper should be a fire proof heavy paper, no idea where to get....
The black tape usually ends up being replaced with scotch tape or black mastic or duct tape.

[Gregory]

Originally Posted by dewickt

Foam tape, I use open cell foam weather strip, closed cell is a bit to firm, available at Lowe's and sometimes Home Depot.
Blue gel can be bought from the factory or Parts Express #244-141 (bright blue).
Backing paper should be a fire proof heavy paper, no idea where to get....
The black tape usually ends up being replaced with scotch tape or black mastic or duct tape.

Thanks for that. I almost bought some gray weatherstrip foam tape from Ace Hardware last weekend on the advice of Vintage Pete, but wanted to get more concurrence. The end-brackets on the inside of the lamp housing are riveted on, and the rivets are rusted. So I may drill them out, pull brackets, remove the goo, replace the fiber board backing, and then re-attach with tiny stainless hardware.

Here are links provided by good bud Doug Olitsky:

Lee Filters Sheets - 117 Steel Blue - Lee-S-117 - - Lights On Retail

and

Lee Filters Sheets - 118 Light Blue - Lee-S-118 - - Lights On Retail


-Gregory

[docdownload]

Hi Gregory
I bought filter film from a local plexiglass and plastic sign supplier it was almost free.
Thanks
Herman

PS nice restoration

[Gregory]

Originally Posted by docdownload

Hi Gregory
I bought filter film from a local plexiglass and plastic sign supplier it was almost free.
Thanks
Herman

PS nice restoration

Thanks for the encouragement.


This is important!! What shade of BLUE would be preferable?


Old Mc blue:




New Mc blue:





-Gregory

[Gregory]

Drill out rivets

More on the MC 2205 Power Meter rebuild subject. This morning I was able to drill out the four rivets that hold the left and right housing brackets in place with no damage to the metal, or even opening up the holes. (all are still 0.137")


Old foam and backing material

The old foam came off with Goo Gone but it was tough scrubbing. Also the backing paper was a mere 0.025" (25 mill) piece of paper or fiberboard. McIntosh Service Dept says the last material used for backing was translucent or frost white plexi-sheet. That should work, but how to attach it?

Here is a view of the housing with brackets and backing removed.


MC2205 meter lamp housing dis-assembled with bracket rivets drilled out.


The metal material has started to rust and corrode in various ways, and applying Deoxit 5 removed some of the tarnish, but applying CLR started to etch the metal. The foam rubber bumpers are still in GOOD shape and can be left in place.

Here are some photos of the rust and corrosion attacking the housing.


Photo showing rust spots and various oxidation of the housing.



Photo showing various oxidation inside the housing. CLR started to etch the surface.


The center and end brackets will be re-attached with #6-32 stainless screws, washers and nuts, as the material is rather thin to re-tap. You can see the center bracket screw which is threaded into the 0.035 think metal. The housing is in fact sheet metal because a magnet sticks to it. The two flange mounting holes at either end are also threaded, and that is VERY thin metal for machine screws threads.


QUESTIONS

Paint the lamp housing - I'm seriously thinking of spray painting the housing with flat black or bright metallic paint to prevent further oxidation and rust. Is there any reason why this would NOT be a good idea? otherwise I'll be going ahead with it.

Attachment of new backing material - What would be a good way to attach the NEW frost white plexi-glass sheet to the back of the housing? Sticky double sided tape? fasteners? metal brackets at the ends? The factory now says the backing wasn't taped or glued in place but rested behind the brackets, but that would imply a rather flexible piece.


-Gregory

McIntosh owner for over thirty years.

[docdownload]

Hi Gregory
I'm going to change my meter bulbs Can't remember the numbers At last time to re calibrate Those druppy meters
Thanks

Herman
Docdownload

[Gregory]

Originally Posted by docdownload

Hi Gregory
I'm going to change my meter bulbs Can't remember the numbers At last time to re calibrate Those droopy meters
Thanks

Herman

Herman.. the meter lamps are #1866. I think the procedure for the meters is: Set amp on level surface and zero the meter movement by adjusting center screw. Calibration requires 8 ohm loads and operating the amp at full power, first in Watts mode then in dB. There's a local Mc dealer that could do the Max Power tests and meter adjust around here.

A lighting and supply company is looking into a new backing material/diffuser for the housing. That's the `long item´ right now, as is re-coating the lamp housing to prevent further oxidation. That housing is made of sheet metal, as a magnet sticks to it. Ron-c was the only one to suggest having it re-plated. I've called a few plating companies, and for sheet metal they're describing a paint job. It's expensive and one guy told me frankly that I could do almost as good at home with some chemicals and spray cans. Still not sure, but I doubt it will be painted black.. maybe silver metallic.

That 2205 meter housing needs some rework, as I believe "through hardware" should be used instead of tapping 0.035" metal for a #6 thread. Best to order the EXACT hardware. I'm starting to replace the screws in my Mc gear with stainless steel. Here is a vendor:

http://www.mcmaster.com/#stainless-s...achine-screws/ -- then click Pan Head.


-Gregory

[docdownload]

Thanks Gregory

[Gregory]

Replacement backing material

The solution for the MC 2205 lamp housing partly came from Terry, but after a visit to a few home centers and craft stores, I was able to narrow down the material to:

a) Shiny aluminum duct tape (no lettering)

b) 4 mil aluminum foil roll

c) 0.009 aluminum flashing roll

d) 0.019 aluminum flashing sheet

The decision was made to purchase a 12" x 12" aluminum flashing sheet 0.019" think and fabricate a reflective backing. There's enough material to make THREE backing pieces in 1 sq-ft, each with a right angle bend, so don't worry too much about making a mistake. The stock might have some edge or corner damage as well. The following pic shows the cut backing/reflector plate.


Lamp housing with 10.7" x 3.4" x 0.019" think aluminum flashing. Simply score several times with utility knife then flex until it yields.



Test fit of 10.7" x 3.4" x 0.019" think aluminum flashing prior to bending.



10.7" x 3.4" x 0.019" think aluminum flashing with bend at 2.48". Clamp between pieces of wood or metal and bend against table top.



With a bit of planning, the first attempt cut will drop right into place, ready to be fastened by the center bracket screw.



A camera flash shows how reflective the new backing material is. Note single screw in the center that will hold the piece in place.


Wrap-up

The cost of the flashing material was $7.49 at the home store, and the whole task including photos took no more than an hour. The original paper backing was 25-mils in thickness, so the NEW material is thinner by ~6-mils, more sturdy and will last longer. Maybe a new gel sheet isn't necessary. I think it would be a good idea NOT to repainted the housing, only polish and a GOOD coat of wax for protection. A couple of rust spots inside will be treated, but it generally will be left stock.


-Gregory

McIntosh owner for over thirty years.