EMI RS124

[snod_donkey]

What you need really is a valve curve tracer.  The point is to get valves where their curves match so they are matched when the compression level changes.  If you have them matched when there is no compression then there is a good chance they won't be matched when you have 10dB of compression happening & the bias is completely different on them.  Something like a Utracer is a good test tool for this.

Nice idea.  I will look into this.  Have to say even when they are a bit off it is not obvious to the sound to my ears

thanks again

 

[Rob Flinn]

In the dozens of units I built in my time, I never noticed anything untoward either as long as both sides were decently balanced at idle.

At the time I started building these I coveted a Tektronix 570 curve tracer but, not having one, I did manually plot out a few valves at one point.  Putting the best matched valve I'd found in a unit,  I couldn't tell the difference in a blind test between that 'golden' valve and another that I'd done my, much easier,  routine on:

Basically, I'd put a valve in, let it heat up and settle, then put the balance pot approx in the middle and measure the two anode voltages at rest.
Providing that was good, I'd run a tone into the unit  at various levels and test the anode voltages at each point.  If they were within a few volts of each other as the anode V climbed, we were good go.

I actually agree with you.  I have built dozens of vari mu compressors of all different types & repaired loads.  I have an AVO Mk4 & a Utracer & have never needed to use either of them the get the units working well.  Some compressors like a gates sa39 or 38 are a bit more fussy, but I have always got a match fairly easily by trial & error.

 

[Bernardo]

Hello good afternoon, I am a fan of audio electronics, I need a couple of compressors vari mu my study but I do not have the comp economy to buy them or send them to build, so I only have the option to assemble them myself.
I have read the whole thread and I have not been able to find how many amps the transformer needs in its two secondary windings.
the voltage of one winding is 6.3v and the other is 117v, but I can't find any amperage.
that is one of my thousands of doubts.
thank you

 

[snod_donkey]

Hello good afternoon, I am a fan of audio electronics, I need a couple of compressors vari mu my study but I do not have the comp economy to buy them or send them to build, so I only have the option to assemble them myself.
I have read the whole thread and I have not been able to find how many amps the transformer needs in its two secondary windings.
the voltage of one winding is 6.3v and the other is 117v, but I can't find any amperage.
that is one of my thousands of doubts.
thank you

Take a look at the valve data sheets that you want to use. This will give you the HT and heater current ratings you require

 

[Rob Flinn]

Take a look at the valve data sheets that you want to use. This will give you the HT and heater current ratings you require

I don't think the data sheets will give you the h.t current, but if you look at the diagram and use the voltages marked on it, then one can calculate the h.t using ohms law.

 

[Bernardo]

Hi Rob, thanks for the pointers, this is not a thread for learners so excuse me.
However, to calculate the ohms law I think you have to know the resistance of each circuit, I have 120v but I don't know what resistance each winding has to calculate the intensity.
thank you very much

 

[Rob Flinn]

Hi Rob, thanks for the pointers, this is not a thread for learners so excuse me.
However, to calculate the ohms law I think you have to know the resistance of each circuit, I have 120v but I don't know what resistance each winding has to calculate the intensity.
thank you very much

Why is this thread not for learners ?
It's nothing to do with the resistances of the windings.  If you actually look at the diagram it tells you that 14.5mA is going through V2.    V1 is simple.  Look at resistor R25.  One side is says 0.2v the other side of it it says 1.1v.  Therefore the resistance across it is 1.1-0.2v.  Using ohms law V=IR you can determine the current that is going through the resistor which is common to both halves of the valve.  All you do is work out what current each valve is drawing in this way & add them up.

 

[Bernardo]

So I think that in the 6.3v section with 2A it is enough, and with about 50ma in the 120v section it can work well.
I think I have the first step, now I need to decipher the rest of the scheme.
There won't be a thread to learn to read schemes of this type?
thank you very much

 

[Rob Flinn]

So I think that in the 6.3v section with 2A it is enough, and with about 50ma in the 120v section it can work well.
I think I have the first step, now I need to decipher the rest of the scheme.
There won't be a thread to learn to read schemes of this type?
thank you very much

That sounds about right.  I found it was easier to find a transformer with about 240v secondary for the h.t, & just  subbed in a circuit with a full wave rectifier.

 

[Bernardo]

Can you explain that better, Rob?
I have a toroidal transformer with secondary1 of 6.3v and secondary2 with 220v, how can I lower the voltage of this second to 120v without having to remove turns of wire and in the way that puts the least risk to my life?
Thank you very much

 

[Rob Flinn]

Can you explain that better, Rob?
I have a toroidal transformer with secondary1 of 6.3v and secondary2 with 220v, how can I lower the voltage of this second to 120v without having to remove turns of wire and in the way that puts the least risk to my life?
Thank you very much

The original circuit uses a voltage doubler to increase the transformer voltage from 115v (from memory) to 230v.  Get rid of the voltage doubler & use a bridge rectifier, then the 220v straight from the transformer will be close enough to 230v to not make any difference.

 

[Bernardo]

Rob I have been thinking about what you comment but I am not able to see it in the circuit, where the voltage is doubled?
the original circuit already brings a kind of rectifier bridge.
I'm sending you what I've deduced to see if it's okay.
Thanks again

 

[Rob Flinn]

You're right.  You will need to use a voltage doubler circuit with your transformer like in the original 436 circuit.

 

[gary o]

Hi folks hope all ok here in DIY world ...I know thread a little old but here goes, I havent DIYed in a while but recently fired up my point to point version of the Rs124 circuit.I made it a few years back it works very well however Im borrowing a inpit transformer from my very old DIY RCA BA6A , ist a Sowter 8540 its spec is 1:4 600r 10K ct. I believe the Sowter input transformer Sowter make is a 1231 listed as a bridging input its spec 1:.23 15K 80K ct.
I dont really understand these specs & its the reason I ask how would the sound change if I got the correct 1231 transformer.... Im guessing I would have less level being 1 to 1 rather than 1 to 4 . I really dont know any thoughts ? thanks... As I say it works great but my Ba6A wants its input tran back & I need to get something for the RS124 , makes sense to buy the correct one.
I rang Sowter today to have quick chat with Brian as he has helped me out over the years & I hear Canford now are Sowter .

Thanks once again , all the best.

 

[gary o]

Ah thankyou so much Winston, thats good news Im always fighting the levels in my little studio anyway, be nice not having to pad things as much...Will wait for a Sowter and will try it in my BA6A too in theory should work in that and again less padding many thanks.

 

[PermO]

When you close the lid, and nothing shorts.... it's good isn't it ? 

 

[emrr]

Looks like a few hundred thread views since my post and Nada.  Zilch.  Crickets...

I was expecting at least some flak for my less than perfect point-to-point wiring or something 

Anyway, plenty of folks have seen  front panel pics of original units but you rarely get to see the rear.
Here's an arse view of a pair of oldies still at A.R.S.

Hahahaha well telco would have failed you or sent you back to wiring school, but really only there. 

I think people are so stunned and amazed by these reveals, they can't speak. 

Best shot I've seen yet.  Now we need some original internal shots!

 

[PermO]

Put in a little switch and a big booby trap capacitor, that will teach 'm  ;D

 

[PermO]

Not to derail this thread any further but...

I sneaked onto a guys workbench and put a distortionpedal between his signal generator and the leads on his bench  ;D

 

[PermO]

About 5 min till he found it.

But the look on his face when that first SKRREERERREXKXKX!!! came out his speakers  ;D