Crossovers were rebuilt with Dayton Audio metallized film caps and bypassed with an Audyn True Copper polyprop film and copper foil caps.  With the covers complete the unit look and sound marvelous! 

Post disassembly, the cabinets look pretty bad but are still solid.  There are no bases, so they will need to be built.  Much of the large panel veneers look pretty good, but the edging veneers are splitting and peeling off, so most will need to be removed and replaced.  Tapping on the larger panels also revealed some ringing which should be damped or at least raised in frequency high enough to avoid excitation.  You can see the panel brace against the back panel from the factory... good that it's there but it's pretty lightweight particle board.  Should be stiffened and mass loaded with something heavier. 

2/4/2015

I picked some pretty beat up Altec Model 19's recently.  The tweeters were blown out but the woofers seemed to work just fine.  The cabinets are pretty beat up but are mechanically sound.  I repaired the tweeters by soldering the broken leads on the diaphragms, and was able to play them via a DEQX crossover and assured myself that these would be good candidates to restore.

First piece of the project is the cabinets.  They need to refinished, for sure, but my Altec expert suggests that they can be greatly improved if the cabinet walls can be damped, so as restoration proceeds I will explore ideas to damp or deaden the boxes while not consuming too much internal volume.  Here are some pics of the de-constructed cabinets.

Luckily, the veneers used back in 1978 were a little bit thicker than what's generally available today.  So most of the panels were sanded to an acceptable level, but the tops of the upper boxes were too damaged in the most visible part of the speaker to let them slide.  So both top boxes were reveneered on the top.  Various repairs were made to the rest of the cabinets.

The original boxes had some pretty large panels that were not braced, so  bracing needed to be added to either 1) increase the resonant frequency beyond what the woofer would be operating or 2) damp the level of resonance to a more acceptable level.  The trade there is that each brace subtracts from the total internal volume.  I read up in the Audio Engineering Society e-library about speaker panel control, and ended up with braces that mostly ran along the long length of the panel to "minimize the radius of a circle" in the unbraced portion of the panel.  That circle would correspond to the fundamental mode of the panel: the smaller the circle the higher the resonance frequency.  Then some damping was added in the form of some constrained layer damping on selected panels and finally, front to back bracing was added to stiffen the front panel.

Restoring Vintage Audio Equipment

The units were dyed and stained and then several coats of Minwax Tung Oil Finish were applied and rubbed out.  The finished boxes were then moved into the audio room for final assembly and testing.  The original fiberglass lining was replaced with Ultratouch Denim Insulation.  The last step will be fabricating and covering the grill panels.  Oh yes, and listening...

Phoenix HiFi

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