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Posts from — November 2016

Inside a Telefunken S600 Belt-Drive Turntable

I had­n’t intend­ed to end up with more than one turntable, but I now have no less than four, all of which work. The most recent one I’ve been work­ing on is a Tele­funken S600, which turns out to be an excep­tion­al­ly well-designed turntable with a num­ber of inge­nious bells and whistles.

As I detailed pre­vi­ous­ly, I want­ed to replace the stan­dard tone arm on a Lenco L75 turntable with an Orto­fon AS-212. These are found (amongst oth­er places) on Tele­funken S600 belt-dri­ve turnta­bles, so I sourced one from Ger­many to steal the arm — but fel­low mem­bers of inter­net groups I belonged to were hor­ri­fied that I would do this to an actu­al­ly rather nice turntable. So I relent­ed, and one of my cor­re­spon­dents found a New Old Stock AS-212 that I duly installed on the Lenco.

Mean­while, the S600 arrived from Ger­many, in rather a sor­ry state. Despite being very well packed, the plas­tic cov­er was cracked almost in two and the back of the arm had gone miss­ing along with the coun­ter­weight. The well-known inter­na­tion­al ship­ping com­pa­ny had both dam­aged it and mis-deliv­ered it: the incor­rect recip­i­ent had opened it and lost some of the bits. So when it got here I would­n’t have been able to pinch the arm for the Lenco anyway.

But now I had learned that these decks were actu­al­ly quite good, I decid­ed to attempt to repair it. And if it was actu­al­ly a good deck, I might want to use it as my main deck — in which case it need­ed a mod­i­fi­ca­tion to run at 78rpm.

Fix­ing the arm

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The big prob­lem was the arm itself. This con­sists of an S‑shaped arm tube with a bear­ing hous­ing on the end made of some mys­te­ri­ous hard rub­bery mate­r­i­al. A small tube con­tain­ing two sets of four 1.2mm ball bear­ings goes trans­verse­ly through the hous­ing and is held in place by two point­ed set-screws that have to be set up exact­ly right so that the arm sits cen­tral­ly in its hold­er with free­dom to move up and down but with no play. The hous­ing has an exten­sion stub on the back, and on to this mounts a thread­ed tube on to which the coun­ter­weight screws. In this case, the stub had snapped off the back of the bear­ing hous­ing and with it had gone the thread­ed tube and counterweight.

There were sev­er­al pos­si­ble solu­tions. Replace­ment bear­ing hous­ings are avail­able on eBay from time to time, made either of Del­rin or brass. The thread­ed tube is avail­able too. I could replace the bear­ing hous­ing (get the hous­ing off the arm tube, push the bear­ing tube through and put it into the new one, add the thread­ed tube and reat­tach the arm). I could con­sid­er get­ting a thread­ed tube and fit­ting some­thing inside it that I could push into the back of the bear­ing hous­ing and glue it in place. I got the bits to do the lat­ter, name­ly the thread­ed tube and some met­al-filled resin. But the pro­ce­dure seemed a bit dodgy, frankly. Would it stay stuck? Would the resin go where it should­n’t? Would it look decent? I looked for a new bear­ing hous­ing instead, but found only brass ones, which seemed like overkill to me — the black Del­rin ones did­n’t seem to to be avail­able at the time. But then a con­tact of mine kind­ly came up with a solu­tion: a com­plete replace­ment arm with the arm tube, bear­ing hous­ing (with bear­ings) and thread­ed tube — plus an orig­i­nal coun­ter­weight. Excel­lent. All I had to do was to fit the arm — and send the old one back to him.

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The replace­ment arm assem­bly duly arrived, and is shown here. The sup­pli­er very kind­ly taped up the bear­ing hous­ing so the balls could­n’t fall out (I had obtained some spares in case they did, but I did­n’t need them). First I need­ed to de-sol­der the arm leads, which meant get­ting the turntable out of its plinth.

This sim­ply required undo­ing three screws. Tele­funken real­ly designed these turnta­bles thought­ful­ly. You lift up the turntable, turn it ver­ti­cal­ly and then you can slide it into grooves in the plinth where it stands safe­ly so you can work on it.

img_2143Here’s the innards of the turntable, and there are a lot of things to talk about here in due course. Click on the image to see it up close. I de-sol­dered the arm wires (they attach to a ter­mi­nal strip bot­tom right next to the mut­ing relay) and then put the deck back in the plinth. I had armed myself with a pair of tiny cir­clip pli­ers with 1mm prongs to fit the lock-nuts sur­round­ing the bear­ing set-screws (one set of both on either side — you can see them in the bro­ken orig­i­nal arm image above) and now attempt­ed to loosen them. Pleas­ing­ly they loos­ened sur­pris­ing­ly eas­i­ly and I was then able to unscrew the set-screws enough to care­ful­ly lift the arm out. Thank­ful­ly the lit­tle ball bear­ings stayed in there too. So I taped it up ready to send off. The new arm went in with sur­pris­ing­ly lit­tle trou­ble too. First I led the wires through the arm col­umn by putting them into a drink­ing straw and push­ing that down the hole in the cen­tre of the col­umn. Then, using a busi­ness card as a feel­er gauge to cen­tre the arm in the mount­ing, I held the arm in place and gen­tly tight­ened the screws. Then hold­ing the screw in posi­tion with a screw­driv­er I tight­ened the lock­nut, first on one side, then the oth­er. It took about three goes to cen­tre the arm suc­cess­ful­ly and lock the screws in place, but the result was an arm that exhib­it­ed neg­li­gi­ble resis­tance when mov­ing in its bear­ings. Exact­ly what was required. This pic shows the new arm in place minus the counterweight.

img_2188The turntable was now back more or less to its orig­i­nal spec­i­fi­ca­tion, give or take. I ran it up and found that it reached 33 or 45 very quick­ly con­sid­er­ing the weight of the beau­ti­ful­ly-bal­anced plat­ter, and the speeds were rock sol­id. The touch but­tons for speed and stop all worked as intend­ed and the speed con­trol trim­mer knobs worked well. I had­n’t even had to replace the elec­trolyt­ic capac­i­tors. (If I had need­ed to, the infor­ma­tion required – along with lots more about these turnta­bles – is here.)

Bells and whistles

This turntable has sev­er­al bells and whis­tles. The main ones are to do with the arm lift. This can be actu­at­ed man­u­al­ly with the lever — there is a Bow­den-style cable from the lifter lever to a flu­id-damped dash­pot under the arm rest. There is a lock­ing arrange­ment that only lets the lever lock in the down posi­tion if the turntable is under pow­er, and if you hit Stop it lifts up the arm (and when the arm is lift­ed, inci­den­tal­ly, the relay men­tioned ear­li­er mutes the audio).

It is also intend­ed to lift the arm at the end of a side. This is accom­plished in a rather inge­nious way. Look at the pho­to of the under­side above and you’ll see that there is a slot­ted cop­per arc just to the left of the motor con­trol board. This is attached to a very light­weight arm that is linked to the ton­earm, and swings across under the turntable as the arm tracks a disc. Just next to the cop­per arc (which we’ll come to in a moment) is a V‑shaped cutout. This is the clever bit. When the arm reach­es the end of a side, that V pass­es between a big frost­ed bulb (just below the cen­tre of the image) and a light-depen­dent resis­tor, shad­ing it from the light. (Why the V I don’t know: it will mean that the illu­mi­na­tion drops slow­ly rather than at once. Why?) This is detect­ed and hits Stop on the turntable, which also pow­ers-down a sole­noid to release the arm-lifter to lift the arm. That is what is sup­posed to hap­pen, but unfor­tu­nate­ly it did­n’t work. In fact it is a lit­tle sur­pris­ing that the turntable would run with­out hold­ing a but­ton down. The bulb had expired. img_2144It looks very much like a W5W auto bulb but it’s only sup­posed to take 100mA. Luck­i­ly there are W5W replace­ment LED bulbs that run that kind of cur­rent so I popped one in. On pow­er-up this duly illu­mi­nat­ed, and now the arm lift­ed and the turntable stopped some­what before the arm reached the end of its trav­el, cor­re­spond­ing to just before the locked groove on a disc.

While we are look­ing under the turntable, let’s look at what that cop­per arc does. As the arm swings, it stops the light from anoth­er, small­er bulb, direct­ly to the right of the main bear­ing, from falling on the end of a light-pipe — that lit­tle clear tube going up to the top of the deck and past the orange string (which is the inter­lock between the pow­er switch and the arm lifter). It ends in a lit­tle bezel on top of the deck. The light is thus vis­i­ble from above the deck except when it’s obscured by that cop­per arc — which means the light is vis­i­ble when the arm is beyond the plat­ter and when the light can shine through the three slots in the arc, which cor­re­spond to the edges of a 7in, 10in and 12in disc. So basi­cal­ly it tells you where to put the arm for the start of a disc.

I thought the dri­ve belt a lit­tle stretched and worn so obtained a replace­ment from thakker.eu (for the S500, a sim­pler ver­sion of this turntable, but with the same motor/subplatter arrangement).

A speed mod

With the deck returned to its orig­i­nal spec­i­fi­ca­tion, next came the mod­i­fi­ca­tion I want­ed to per­form — to get it to run at 78rpm as well as 33 and 45. I had asked about this in the Vinyl Engine online forum and a gen­tle­man had kind­ly looked at the cir­cuit dia­grams I had found and sug­gest­ed how to do it. It turns out that this design of turntable was actu­al­ly licensed from Philips, though Tele­funken made some exten­sive sub­se­quent mod­i­fi­ca­tions. It’s a DC ser­vo-con­trolled motor arrange­ment, and in some of the orig­i­nal Philips mod­els using the same motor and con­trol board design, the turntable can actu­al­ly do 78 rpm right out of the box — so there was no rea­son why this should­n’t work.

The answer, my respon­dent sug­gest­ed, was to put a resis­tor across the main 45rpm speed con­trol resis­tor (R133) to reduce its val­ue, then use the 45rpm speed knob to fine-tune the speed to 78. I decid­ed to go a lit­tle beyond that and put a trim­pot in series with the fixed resis­tor so that I could set the speed to 78 with the 45rpm speed con­trol knob in the cen­tre posi­tion as it was for 45, and not have to adjust any­thing unless I want­ed to run at a spe­cial speed like 80rpm for exam­ple. It took some exper­i­men­ta­tion to get the val­ues right: even­tu­al­ly I used a 47k? fixed resis­tor in series with a 10k? trim­mer. I sol­dered these to a minia­ture DPDT tog­gle switch that I mount­ed in the low­er right-hand side of the plinth, with a hole to access the trim­mer, and a LED and series resis­tor, pow­ered from the lamp sup­ply, on the oth­er poles of the switch so a red light comes up when you select 78. And it works beau­ti­ful­ly — here’s a Con­roy music library 10in 78 spin­ning at the right speed!

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Final­ly, I replaced the audio out­put cable, adding a pair of Neu­trik phonos in place of the orig­i­nal 5‑pin DIN, and ran a chas­sis ground wire along the audio cable with a spade con­nec­tor on the end. In fact this is of lim­it­ed use as the mains on the turntable goes via a dou­ble-pole switch straight into a dou­ble-wound trans­former: the chas­sis and all the audio grounds are con­nect­ed togeth­er and have no con­nec­tion to the mains side. Untan­gling this to pro­vide sep­a­rate audio and chas­sis ground turned out to be a real pain — to retain the mut­ing relay func­tion would have required seri­ous rewiring — so I left well alone, and in fact it works fine, and the chas­sis can be con­nect­ed to mains earth if desired.

The turntable has a cast stro­bo­scope at the edge with its own neon lamp, but of course it does­n’t include 78, so I print­ed out an image of an old Gar­rard strobe for now and that works fine — maybe I’ll pick up one of the Lenco met­al ones at some point.

In oper­a­tion

img_2197So, now to try the turntable out. I mount­ed the Shure M97xE in a skele­ton head­shell orig­i­nal­ly acquired for my TT-100 and set it up for 16mm over­hang (tricky as you can’t move the arm to the cen­tre spin­dle: I cut a piece of wire to length as a mea­sure) and lined it up with a car­tridge pro­trac­tor: it lined up per­fect­ly. Set­ting the track­ing weight and anti-skate accord­ing­ly, I played a tone disc with the arm at dif­fer­ent posi­tions and the wave­form and sound were clear and undis­tort­ed through­out. I then played some music, and found this under-recog­nised turntable, believed by many to out-per­form many oth­er belt-dri­ve turnta­bles of the peri­od such as those by Thorens, was a mar­vel­lous per­former, deliv­er­ing an excel­lent, open and sta­ble sound just as I would like it.

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The only prob­lem I have now is what to do with all these turnta­bles. I real­ly don’t want to get rid of either the Lenco or the Tele­funken and I think the for­mer will end up on the main sys­tem down­stairs while the Tele stays in my stu­dio for tran­scrip­tion (along­side the excel­lent Tech­nics SL‑7 lin­ear track­er, which does­n’t do 78).

November 3, 2016   17 Comments