Philips EL3541/15K Tape Recorder

[SteveCG]

This is a single speed (3 3/4 ips), 1960/1961, 1/4 track mono machine.

My simple question is this:

Does the tape counter drive belt go around the supply reel (LHS from the front) or the take-up reel (RHS) mechanism?

[Aerodyne]

The manual isn't very clear on this point but it definitely looks like it goes around the supply reel side.
Tony

[SteveCG]

Thanks Tony.

Before contacting the forum on this I had noticed that the tape counter sits symmetrically between the supply reel and the take-up reel mechanisms. Gently turning the counter and then the reels showed that either position would work. Unless somebody else has an even more definitive opinion I'll go with Tony's.

[Ted Kendall]

Convention tends towards the take up reel, lest the counter impose drag on the supply reel and cause tension fluctuations and hence wow.

[TonyDuell]

Oddly, just about every tape recorder (reel to reel and cassette) that I've worked on drives the counter from the supply spool. Maybe it causes wow but they were designed that way. So in the absence of any other information I'd go with the supply spool.

[julie_m]

There is no shortage of machines with the counter driven from the supply spool, though! The Akai 4000 DS even does it this way with a 4-digit counter (i.e., three levels of carry; potentially more drag, as 9999 changes to 0000).

EDIT: Posts crossed.

[Ted Kendall]

Well, for "convention", read "best practice", then. Revox and Ferrograph certaiinly did this - I think the placing of the counter was an afterthought in many machines, though.

[radiotechnician]

The left , or supply side.

The Philips machines of the era, there were 3 in the 60s:

EL 3536, EL3541, EL3542, North America, and a few versions of the
single speed model from Europe, used the same turntables.

Repairs on these and others was my work then.

Since they used the same counters, tape indices would be correct
on any model.


I have looked at the single speed models, and here is a mechanical layout:

[SteveCG]

Thank you Steve for the definitive mechanical layout diagram!

Thinking on the topic I wondered whether the supply side was chosen so as to make sure there was sufficent back tension to always keep the tape in contact with the Erase head - important during recording?

The Record/Replay head has a pressure pad - but not the Erase head. Moreover this machine does not have sprung-loaded guides (like the Ferrograph Series 7 say) to keep the back tension up.

[radiotechnician]

Back tension is provided by the stationary plastic disk , item 126,
which is held stationary by the slot in lever 87.

Disk 126 differs from disk 83 on the takeup side which has a pin
descending into (spinning) drive wheel 89. That is the origin of
takeup tension.

Both disks engage the felt rings glued onto bottoms of the turntable.

Also, nothing will work properly unless washers 132, 133, 134, and 136
are in place and properly chosen during adjustment.

At one point, Philips sold these washers in kit bags. Different thicknesses
were available.

All the turntable systems are gravity engaged.

[ricard]

Also, I would add that the drag from the counter is (should be) much less than the friction between the turntable its felt ring and the underlying plastic disk. There's not a lot of back tension on this machine, just enough to keep the tape form lifting from the erase head. The pressure pad at the record/playback head holds the tape firmly in place at this crucial point.

Some slightly later Philips machines, I know the EL3547 does it this way, have a small spring loaded pad at the left guide pin, and no back tension at all on the reel tables. Yet the counter still operates from the left hand turntable, and there's no discernible drag from it.

Which puts me in mind - it seems that this way of using vertically arranged clutch mechanisms with felt rings on the turntables engaging with stationary or spinning disks was more typical of 1950s construction that later designs. I don't know if it is the fact that these machines can be hard to set up regarding the actual tension induced, or that later designs attempt to be more compact vertically. Tandberg is one manufacturer that kept using the vertical clutch arrangement for the longest time, but other manufacturers seemed to move towards having rubber idlers engaging against the reel tables to provide various functions.

[radiotechnician]

There are tension specifications. For a full 5 inch reel with a radius of 2.3 inches on the supply side, the resistance should be 0.026 lbs. On the right
takeup reel it is 0.05 lbs.

Philips (did) mention that the method of obtaining this is by degreasing the felt and friction disk with carbon tetrachloride.

Dont !

I wrote an article in PF Reporter magazine in August 1965 and listed
Carbon Tet as a degreaser. Even then, there was much flack sent my
way, over that chemical.

http://www.americanradiohistory.com/...er-1965-08.pdf