TD 124 Wakes Up

[jls001]

Today I spent the better part of the afternoon in opening the 124. Following things done:

1) Replaced the wrong value cap with correct value. Since the contact remained doubtful when I simply screwed it to the power inlet block, took the extra trouble of soldering it across the incoming power points.

2) Changed the ground cable to another, longer one.

3) Extended the ground from the tonearm to the turntable chassis ground point.

4) Opened the speed selector switch. Then realised that the 33 rpm point not engaging sometimes has nothing to do with the selector switch, so lamely had to put back the selector switch.

5) Cleaned the electrical contacts using earbuds laced with iso-propyl alcohol. This alcohol was absolutely no good to clean up the grime on the painted outer surface or the speed selector faceplate.

6) Ended up kitchen-grade cleaning cream called Cif to clean up the enamel painted surfaces and the speed selector faceplate. It did a very fine job - highly recommneded to clean your TT. Do make sure you use a damp cloth the wipe off the detergent.

7) Brasso-ed the platter. Now it's real shiny.

8) Adjusted the mechanism which engages the idler wheel. Now 33 rpm engages unfailingly. But 16 rpm has decided to take a break! Doesn't matter as I don't have any 16 rpm record. 45 and 78 rpm also engage fine.

All in all, a good Sunday afternoon.

 

[jls001]

Shiny faceplate of the speed selector switch - 50 odd years of dirt and grime washed away.

By jls001 at 2012-03-11

Notice the shiny platter. Generous daubs of Brasso metal polish and many rounds of buffing gave it a new-found shine. Also note the cleaned-up enamel painted surface.

By jls001 at 2012-03-11

 

[malvai]

awesome! looking tooo cool!

 

[sachu888]

Joshua,TT looks really nice.

Regards,
Sachin

 

[stevieboy]

Wow looks pretty spotless and brand new! Thanks fir the cif cream tip!


Tapatalking. Look ma, no computer!

 

[Hiten]

Neat job Joshua.

 

[jls001]

I have a query about capacitor replacement in the TD 124: the service manual for the turntable says one should replace the 0.01uF capacitor "if a popping noise occurs in the speakers when the on-off switch is operated". This capacitor is

I managed to find a 0.1 uF, 250V film capacitor. This is 10 times the recommended value. Is it safe to use it, or should I use only 0.01uF?

Reviving a very old issue that bugged my Thorens TD 124: as mentioned above the turntable produces a loud thumping noise on the speakers whenever the on-off switch is operated. it even picks up electrical impulse when light or fan switches are operated in the same room.

I had tried putting a 0.01uF/630V capacitor across the mains tag block but it didn't help. I had mostly ignored the problem as I always had another TT in the room. Also, there was a workaround - use the switch with preamp volume set to zero. BUT these were just workarounds and not solutions. I have searched for answers on the net but found nothing that could resolve my problem. Of one thing I was sure of - the noise was electrical impulse being picked up by the TT. Only problem was I couldn't figure out what was acting as an antenna to pick up the electrical impulses (like the sparking that occurs when one operates domestic switches electrical switches). Yet another round of recent search led me to an YouTube video of a restoration of a TD 124. And that video showed me exactly where I should be put the spark suppressing capacitor. This is embarrassing, but I've been fitting it at the wrong place. Here's the correct location: it must be fitted electrically parallel to the on-off switch for it to work correctly.

A note about spark suppressing capacitors: they're usually rated X1 or X2. X1 is rated for 400V. X2 for 630V. One must use the correct X rating (besides correct capacitance value).

To add: since I was anyway opening up the TT, I thought I will oil it. I tried my usual sewing machine oil and found a pronounced ticks and pops. I added some lithium grease in the hope that it will make the oil thicker. It helped. Later I cleaned the oil-grease mixture after I realised that grease clogs the pores of oilite-type bronze bushings, preventing self oiling. I now use Mobil 10W30 Delvac diesel engine oil. It is much thicker than sewing machine oil and it produces a solidity in the sound (I like it). Also cleaned idler wheel rubber (using Zippo lighter gas) and oiled various moving parts.

 

[greenhorn]

Brasso-ed the platter. Now it's real shiny.

I'd suggest you wax or apply some sort of protective polish to the metal platter. After using brasso, if you leave the surface bare, it can become dull very easily!

 

[jls001]

I'd suggest you wax or apply some sort of protective polish to the metal platter. After using brasso, if you leave the surface bare, it can become dull very easily!

Thanks for the suggestion. Good idea! I do have lots of wax. It's been years since I buffed it and surprisingly it's still quite shiny but I will buff it again and finish it with wax.

 

[jls001]

Update:
Fitted correct rating capacitor - X2 rated 0.01 uF. Added a 220 Ohms 5W resistor in series to the capacitor to act as "snubber" which will limit current rush (idea lifted from Garrard 301 - thanks, TD150 for the pointer).

Now the switch operates in complete silence.

Strictly speaking, the AC voltage rating is still on the lower side. Ideal would have been 445 VAC to make DC rating 630V -> 630/sqrt(2) = 445VAC. Will try to get higher rating in future. But for now I am hoping the series resistor (a silicon resistor) will help limit inrush current and help preserve the cap.

 

[IndianEars]

300 Volts AC = 300 x 2 x Root 2 to calculate the Peak To Peak Voltage of AC
= 300 x 2.82 = 848 Volts Peak to Peak ....

Hence 300 V AC rating is equivalent to 848 Volts DC rating.

The Capacitor you have choosen is a Metalised Polyester Cap. These have good 'Self Healing' properties. Excellent Choice. :thumbsup: Stay with it.



The 5 Watt resistor is probably wirewound and therefore Inductive. Hence a carbon resistor would have been better suited for this duty, since a carbon resistor is non inductive. Ofcourse you would need to use 2 or preferably 3 carbon resistors in series to ensure that the carbon resistors do not suffer Voltage breakdown ( Typically rated at 250 V DC...,. called the Characteristic Voltage on the data sheet)

However, since you have eliminated the Switch-On noise, stay with what you have incorporated. CONGRATS ! :cheers:

 

[peace_sells]

300 Volts AC = 300 x 2 x Root 2 to calculate the Peak To Peak Voltage of AC
= 300 x 2.82 = 848 Volts Peak to Peak ....

Hence 300 V AC rating is equivalent to 848 Volts DC rating.

Don't mean to be rude but 300V peak sine signal = 848 Vrms??? The DC equivalent of an AC signal is never greater than the AC peak voltage. RMS voltage of 300V peak sinusoid = 300/sqrt(2) which is roughly around 212 V.

 

[IndianEars]

peace_sells

No offense taken to yr query.

You are correct regarding the Relationship between the Peak AC voltage and the AC RMS value for a sinusoidal waveform.

AC RMS = AC Peak Divide By Root 2 ( as you have mentioned.

Incidentally if we refer to Peak-To-Peak voltages

AC RMS = AC Peak -To-Peak Divide by 2 x Root 2

1. I have however not said what you have mentioned:

300V peak sine signal = 848 Vrms???

I had in fact said :

300 Volts AC (I should have mentioned RMS) = 300 x 2 x Root 2 to calculate the Peak To Peak Voltage of AC
= 300 x 2.82 = 848 Volts Peak to Peak

The Capacitor experiences Voltage Stress from the Peak-To-Peak Voltage.

The RMS (sometime referred to as DC Equivalent) is the amount of work / heat that you can get out of the waveform.

I feel its not relevant here in determining the Voltage Stress on the Capacitor.

Hence I have stated that the 300VAC rating capacitor is capable of withstanding the stress of 848 Volts DC.... ie a 300VAC rated Capacitor would work well in the snubber circuit used by jls001 & there is no real need to replace it with a higher voltage rated capacitor, in future.



P.S: Nice Diagram of RMS, Peak & peak To Peak for a Sine Wave is on Wiki

 

[jls001]

See here:Antique Radio Forums • View topic - AC/DC Capacitor Voltage Rating Question

It concurs 100% with what IndianEars is saying. So my cap is more than safe.

 

[peace_sells]

peace_sells

No offense taken to yr query.

You are correct regarding the Relationship between the Peak AC voltage and the AC RMS value for a sinusoidal waveform.

AC RMS = AC Peak Divide By Root 2 ( as you have mentioned.

Incidentally if we refer to Peak-To-Peak voltages

AC RMS = AC Peak -To-Peak Divide by 2 x Root 2

1. I have however not said what you have mentioned:


I had in fact said :


The Capacitor experiences Voltage Stress from the Peak-To-Peak Voltage.

The RMS (sometime referred to as DC Equivalent) is the amount of work / heat that you can get out of the waveform.

I feel its not relevant here in determining the Voltage Stress on the Capacitor.

Hence I have stated that the 300VAC rating capacitor is capable of withstanding the stress of 848 Volts DC.... ie a 300VAC rated Capacitor would work well in the snubber circuit used by jls001 & there is no real need to replace it with a higher voltage rated capacitor, in future.



P.S: Nice Diagram of RMS, Peak & peak To Peak for a Sine Wave is on Wiki

Ah sorry..I was not fully aware of the context. I din't read this comment of yours

"300 Volts AC (I should have mentioned RMS) = 300 x 2 x Root 2 to calculate the Peak To Peak Voltage of AC
= 300 x 2.82 = 848 Volts Peak to Peak"