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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 1st May 2022, 5:27 pm   #1
stevehertz
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Default Philips 634a chassis mounts and rear cover loop

I recently revisited my Philips 634a on which I’d completed a full restoration back in the early 80s but wanted to check a few things and fix a few remaining niggles. A couple of these things were the special rubber washers and metal spacers that hold the chassis in the cabinet, and the cloth loop that enables the back to be pulled away from the integral mains plug.

On my 634a, apart from one where remnants remained, three of the original rubber chassis mounts were missing and the chassis was simply bolted down onto the wooden cabinet floor. I assume the rubber mounts are there to provide a degree of acoustic isolation from the chassis in order to reduce microphony via the speaker to the valves. Also, the mounts serve to lift the chassis a tad such that the pot shafts and knobs are central to the holes in the front of the cabinet.

From the remnants that I found of one mounting, from what I can tell it comprised of a special ‘top hat’ shaped rubber washer on the top of the cabinet floor, and a flat one beneath. Running through the washers is a metal tube or spacer such that when the mounting bolt is fully tightened there is still a certain amount of tension left in the rubber washers, but the mounting is sound and tight. These tube spacers are a tight fit in the rubber washers.

Faithfully replicating the mounts would necessitate sourcing rubber washers and spacers of the same shape and size as originals. Unsurprisingly, this is not possible. I used grommets from a Workzone set of 125 grommets. In addition I used some metal spacers that I just happened to have in stock that measured 1” (25.6mm) – exactly the same length as the original ones, but wider at 10mm which fortuitously fitted the aforementioned replacement grommets perfectly! See photo of original and new spacers.

As annotated in the Workzone box, the grommets I used were sized as follows: 4 off 9.53mm x 11.91mm, and 2 off 9.53mm x 20.64mm. Straight out of the box they needed an amount of reshaping to achieve the correct shape and function. The smaller ones are used for the top hat shaped mounts on top of the cabinet floor and it was necessary to remove one of the ridges using a scalpel to carefully skim it off, leaving the area of the rubber tube underneath the ridge in place – see grommets on the left hand side of the photo for before and after. ie do not simply chop one ridge off. The other grommet was cut (split) into two, one side first, flush, then removing the remaining excess rubber from the other one to achieve two flat rubber washers – see grommets on right hand side of photo for before and after.

It is then a relatively simple matter to fit the grommets and spacers to the holes in the cabinet base, fit the chassis and tighten the 5mm bolts until all slack is taken up as the chassis and the bolt head (with washer) contacts the spacer at each end. At this point there is still some tension in the rubber mounts – perfect.

Removal of the back (rear cover) of the 634a can be a bit foxing as it is an integral part of a mains plug and socket arrangement such that (in theory) the set cannot be live without the back in place. To this end the back is equipped with a cloth loop that is used to pull apart the plug and socket allowing the back to come away. Due to ageing of the cloth, on most sets this loop is broken, making it difficult to remove the back. In essence it’s just a relatively simple matter of replacing the loop. First off you need to drill the original rivet mountings out from the rear of the back, I used a 6mm drill. You only need to drill down a tad for the original rivets to come away.

I used a cyclist’s pedal nylon toe strap to fashion a suitable new loop. The strap is exactly the right width and thickness to fit through the slots in the back. Having cut a length of strap to the correct length and threaded it through the slots I then used a flame to seal the ends of the strapping. I used a leather workers punch to form the holes in it. I then pop riveted the strap in place re-using the original washers to ensure a strong mount that will last for another 90 years.
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Old 1st May 2022, 5:29 pm   #2
stevehertz
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Default Re: Philips 634a chassis mounts and rear cover loop

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