Belt threading on Philips EL3549

[ricard]

A while ago I got a Philips EL3549 as part of a bumper purchase of recorders at an antique radio auction, but have only recently gotten around to taking a closer look at it. I've always been a bit intrigued by these 4-speed machines, and I'd actually never had the opportunity to take a look inside one of these.

Upon opening it I found that the rewind belt had not unexpectedly turned to goo. (The other rubber parts seemed fine though; the counter belt was missing completely; the main drive idler had a few flats which I've managed to alleviate to some extent by sanding it down). Bits of the belt were lying in various places, and the mere thought of touching any piece instantly transformed it from square cross-section belt to a sticky black mess. After cleaning up the mess, I was going to attempt to fit a spare belt I had lying around, probably not intended for this machine, but would fit well enough for the time being. It was now I came to the realization that for the rewind reel to turn in the proper direction, the belt must be threaded in a figure-8-fashion. Not having the service manual at hand, I cannot figure out any other way to thread it; any other threading would require an idler somewhere which I cannot find. Indeed, from a picture at radiomuseum.org it does look like this is indeed the case.

Can anyone else confirm the figure-8-threading? It seems odd to me because that means that where the belt crosses itself it would be rubbing against itself which I would have thought would lead to a lot of wear and rubber dust all over the place.

Mechanically this machine really is a halfway house between earlier machines with chunky mechanical parts, to later machines such as the N4308 with its multitude of linkages, petite partsz and nylon idlers.

[Steve_P]

Do it properly and with instructions - This machine deserves it.

http://www.ebay.co.uk/itm/Belts-for-...-/110855785761

It's only £11 - Well worth it.

I have no connection with the seller in any way shape or form and this Ebay link is for information purposes only.

Cheers,

Steve P.

[ricard]

Thanks for the tip, might well order a set, they don't seem too common, and the length and cross sectoin is probably more critical than in general, as it's the back of the belt that drives the left reel table in rewind mode, and the belt tension has to compete with the tension of the spring pulling it towards the left table.

That said, I found a makeshift solution, by rethreading the belt; I took a square section belt and threaded it around the knurled part of the left reel table that it normally just makes contact with when threaded round the idler. It then runs over the idler to get it in the right position for the trail towards the right (nylon) idler. I had to file a couple of mm away from the left brake arm so the belt wouldn't rub against it. Perhaps not an ideal solution, as it seems to add a bit of friction to the left reel table (but on the other hand I don't get loops in play mode when starting), but at least a way to get the mechanics working while I go through other parts of the machine to see what else looks looking to.

I'll see if I can post a picture, it's easer than describing it.

The quiescent current in the output stage (slightly oddly enough a class A output stage with an OC26) was off, causing the output volume to be too high and slightly distorted. A simple adjustment gave me a good sounding output. The output stage is typically Philips, with a three-coil output transformer; one is the primary and internal speaker secondary, as an autotransformer, another is for the external speaker output and also used for negative feedback. The third coil is just connected via a resistor and capacitor to +15.5V, so in normal use there's no current flowing through it. The only reason I can think of is some form of anti-thumping turn-on circuit (counteracting some other current flow in another winding), or possibly some form of bootstrapping.

[dmaillard]

Hi,
Here's some pics that may help. This is for the WR00 version of this recorder.

Cheers
David

[ricard]

Thanks for the pictures! Apparently (among other sources the eBay link above), WR 00 is different from later versions. And comparing the pictures above with my machine I can see that is definitely the case.

On my machine (it's a WR 04, made in 1963), the right-hand pulley is made of nylon, the middle pulley is missing and has been replaced by a pulley just to the right of the left-hand reel table. As designed, the belt does not loop around the left hand reel table at all, the pulley having been replaced by a knurled roller instead. The belt instead loops around the pulley just to the right of the reel table, which moves to the left in fast rewind mode, forcing the back of the square section belt to make contact with the knurled roller which is part of the left-hand reel table, in order to provide the drive. In order to get the reel turning the right way, the belt must be crossed over, in a figure 8 manner, which looks ludicrous, but I cannot see any other way; it's consistent with pictures and a diagram I've now seen in the service manual. I would have expected there to be lots of rubber dust from the belt having rubbed against itself in opposite directions, but couldn't see anything to that effect, so apparently it works.

Radiokmuseum.org has a picture which shows it, not too clearly though:

http://www.radiomuseum.org/r/hornyph...t_wm_34.html#a

After the modification I've made, it works more or less as the pictures above though, with the difference that the middle pulley is much further to the left, as it was originally intended to make contact with the knurled roller on the reel table.

I wonder why Philips changed the design? Since it was done so early in the revision history of the machine, I would think there was some sort of a major problem with it. Indeed, a machine with a similar design (and identical button arrangement), the EL3548, as the simpler design with the belt running around a pulley on the reel table. This machine has a different motor placement though, so the belt is shorter.

BTW, the belt in the above pictures looks like it has a round rather than square cross section, so I assume it has been replaced?

[ricard]

Some pictures of my new belt arrangement. The machine itself is a WR 04 version. Note the different arrangement and types of the pulleys compared to the WR 00 above.

Note that I'm not saying this way of threading the belt has any special advantage compared to the original figure-8-threading, save for the fact that I happened to have a belt that was too long to fit the way originally intended, and that I couldn't really get my head around the way the fbelt apparently rubs against itself due to the figure-8 pattern. Also note the little cut-out I had to file in the left hand brake mechanism so the belt wouldn't rub against it.