EMI RS124

[rouni]

Hey manu! Looking amazing , congrats!

Do you happen to have any of the P2P schematics or info still available? I'm really thinking of building this and I would greatly appreciate it!

Hi! There is no p2p schematics, i followed partially the EMI original schematics you can find on this thread. I mixed it with some caps values of the others 6al5 varimu like ua175, etc.... for highpass detection and release cap.

 

[rock soderstrom]

Hi guys, I'm planning my first RS124 build and I'm wondering, how often do I have to use the balance pot, does it really have to be on the front panel or is it enough to position it on the back? What do you think?

 

[Rob Flinn]

Hi guys, I'm planning my first RS124 build and I'm wondering, how often do I have to use the balance pot, does it really have to be on the front panel or is it enough to position it on the back? What do you think?

On the front is useful.

 

[rock soderstrom]

Thanks Rob

 

[rock soderstrom]

I just wanted to redraw the original schematic to make it easier to read. But it's already done, Member @jozu posted this in the documents section, it fits well here, too.


Thanks!

Edit: keywords RS124 schematic, Schaltplan, Schéma électrique

 

[thomasdf]

Amazing ! I was away in the countryside and spent a day redrawing it on paper haha. I didn’t know of such a redraw !

In the end, what’s the general opinion regarding the power transformer ? The Altec one seems to deliver 117V, but the RS124 one leans toward 255/1.44 so around 180V. From what I read in this thread the lower the HT, the smoother the compression?

The other weird thing for me is the heater wiring : grounded on one side, looks like the best way to mess up the ground. But clearly indicates that aside the primary being different in US / UK, the power transformer is not the stock Altec.

 

[Rob Flinn]

Amazing ! I was away in the countryside and spent a day redrawing it on paper haha. I didn’t know of such a redraw !

In the end, what’s the general opinion regarding the power transformer ? The Altec one seems to deliver 117V, but the RS124 one leans toward 255/1.44 so around 180V. From what I read in this thread the lower the HT, the smoother the compression?

The other weird thing for me is the heater wiring : grounded on one side, looks like the best way to mess up the ground. But clearly indicates that aside the primary being different in US / UK, the power transformer is not the stock Altec.

I used Rcore transformers for my builds, I can't remember exactly what the spec was but I got them from a French company and they were only about 25euros each. Unfortunately I can't open the boxes up and find out the spec, because my RS124's are at my house in in Aude & I'm in the U.K for the moment. It might have been something like the link below with an appropriate dropper resistor.. I found when grounding the heater winding that the fact that is is grounded made a lot more difference than whether it was grounded by a centre tap or resistor divider. Although obviously the resistor divider or centre tap are preferential.

https://www.ebay.co.uk/itm/27324541...oLY0CCj0C3z/Cvem/YXd2uCWmxoR|tkp:BFBMrpOx6-Jj

 

[rock soderstrom]

Amazing ! I was away in the countryside and spent a day redrawing it on paper haha. I didn’t know of such a redraw !

I was also about to redraw the schematic, then I thought I should search for it using the forum search function. Voilà, direct hit!

One schematic is drawn for 200 Ohm output impedance, the other for 600R. I haven't checked both properly yet, but it looks good so far...

It might have been something like the link below with an appropriate dropper resistor.

Where did you install the dropper resistor, directly after the rectifier or simply increased R12 and R13 accordingly? Did you give the power supply a little more capacity or did you proceed exactly as planned?

The R124 has really little ripple filtering! It's very unusual for me, but it's also my first symmetrical circuit project...

 

[Rob Flinn]

Where did you install the dropper resistor, directly after the rectifier or simply increased R12 and R13 accordingly? Did you give the power supply a little more capacity or did you proceed exactly as planned?

The R124 has really little ripple filtering! It's very unusual for me, but it's also my first symmetrical circuit project...

The dropper would have been after the rectifier. I don't know what value it was because I built these boxes over lockdown & I'm not good at keeping notes of what I did. I am not going to France now until July so won't be able to look at what I did unfortunately, but it's not exactly rocket science.

 

[rock soderstrom]

The dropper would have been after the rectifier.....but it's not exactly rocket science.

That's true, but I wonder (as a trainee rocket scientist ;-) if a series resistor after the rectifier doesn't affect the voltage divider that feeds the “balance” circuit?

Anyway, I'll include a series resistor of sufficient wattage in my PCB design so that different transformers can be voltage matched.

 

[Rob Flinn]

That's true, but I wonder (as a trainee rocket scientist ;-) if a series resistor after the rectifier doesn't affect the voltage divider that feeds the “balance” circuit?

Not sure why you would think it does. The voltage divider would be after the dropper too..

 

[rock soderstrom]

Not sure why you would think it does. The voltage divider would be after the dropper too..

I'm not sure if I'm making a mistake, but the additional series resistance would add to the upper part of the voltage divider, right? But the corresponding value would probably have little effect on the ratio of the two 100k resistors. I think we can file this under brain fart

 

[Rob Flinn]

I'm not sure if I'm making a mistake, but the additional series resistance would add to the upper part of the voltage divider, right? But the corresponding value would probably have little effect on the ratio of the two 100k resistors. I think we can file this under brain fart

You just select a dropper that provides 265v to junction r13, r14, r18 & c7.

 

[rock soderstrom]

I'm tempted again to make a bunch of mods from scratch. Canceled - I'm building the compressor as originally intended. What was good enough for the Beatles should be good enough for me as well.

 

[rock soderstrom]

Which neon lamp do you use for the balance oscillator? It seems to be a 110V type. Is there anything else to consider apart from the voltage? Source?

 

[thomasdf]

Haha Rock ! We are having the same questions and reflections one day after another. Seems like the modern equivalent would be the A1A / ne2 model. I have bought a 65/95V version from banzai, I’ll see if it blows up or not. It looks like it is responsible for the oscillation freq clicking because as soon as the voltage reaches its operating point it lights up and leaks to ground ?

 

[rock soderstrom]

Haha Rock ! We are having the same questions and reflections one day after another.

Yes, it seems we are on the same path!

Seems like the modern equivalent would be the A1A / ne2 model. I have bought a 65/95V version from banzai, I’ll see if it blows up or not.

I also have two NE2 with (I think) 60V left over from my LA2A project. I have not yet been able to find a 110 volt type among the usual suspects.

It looks like it is responsible for the oscillation freq clicking because as soon as the voltage reaches its operating point it lights up and leaks to ground ?

It could be like that. I'll be honest, I'm not entirely sure how it works. We'll see when we build it! Good luck!

Edit: What would a 95V type change, the frequency of the click?

 

[thomasdf]

More like the level ? If the AC rises to 65 / 95 / 117V before discharge it's more about the level I suppose ? But maybe someone in the know can chime in !

Edit : I bought a pair of A9A from Banzai. 65-95V ... so they will probably blow up haha. The original calls for 110V indeed

EDIT : scratch my previous comments ! It's is DC that's being fed to the neon ... so the facts that it lights one & off is creating the ticking noise / low freq oscillation I suppose.

 

[Rob Flinn]

I managed to find some 110v bayonet fitting neons on ebay which work great & are easy to replace if one dies on me.

 

[Murdock]

I used Rcore transformers for my builds, I can't remember exactly what the spec was but I got them from a French company and they were only about 25euros each. Unfortunately I can't open the boxes up and find out the spec, because my RS124's are at my house in in Aude & I'm in the U.K for the moment. It might have been something like the link below with an appropriate dropper resistor.. I found when grounding the heater winding that the fact that is is grounded made a lot more difference than whether it was grounded by a centre tap or resistor divider. Although obviously the resistor divider or centre tap are preferential.

https://www.ebay.co.uk/itm/273245416686?itmmeta=01HWBBC95YXEMFEV9Q0C6W6Y60&hash=item3f9eb22cee:g:GusAAOSw5i1fGBxg&itmprp=enc:AQAJAAAA4BXtM8OGABh75FVgFjL47UY2PZs0GrBAomUsNPk5pO4Nc6IoBC5oaAy2QW7lZQ56mNSuWjlLUZS+DaQhSf6r4YO7I1TTnkijExK6xUVkM5zE6YvGYwABoer+xVP5v5AtSCYb+LYlUPix5Ngssq73KDMDYotVllwZO7eACZCB/XAQ7gYmzAIqk54Wsx6304rDSd/1B8rRmGfToez4RMYwhxpmnjvqJ+uuGwl3RD54/nplG5ECo4aTZwv7yZZX2seN+E1hNo0PCAng1sKtoLY0CCj0C3z/Cvem/YXd2uCWmxoR|tkp:BFBMrpOx6-Jj

I think this one was the transformer you once linked to:
https://www.audiophonics.fr/en/r-co...Cr2-NRgF4h9Ugi11VJVDFSJlAhfjTFL7qKPZRLgUml6t8

But this one also seems even more appropiate (less voltage to drop) when you're ok with using AC heaters:
https://www.tubetown.net/ttstore/de/ringkern-netztrafo-30va-8808.html