EMI RS124

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gary o

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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.
 

Winston OBoogie

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Hi Gary,
You shouldn't need the extra gain of the 1:4 600:10K so I would just get a 1: 1+1 like the original.

Sowter seem to be backlogged at the moment so hopefully you won't have to wait too long.

Lundahl make a good one that'd work too but I think it might be more expensive.

 

gary o

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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.
 

Winston OBoogie

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If the padding down you need to do on your BA6A is into the unit then yes, it'd be fine there too.

BA6A's are a bit of a beast in terms of output capability though so, if your padding down is on its output, just use a 1K log pot as an output attenuator.  Unless your unit already has an output attenuator in which case, ignore that bit and just carry on as normal :)
 

Winston OBoogie

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Just for fun, possibly informative for anyone converting an original Altec:
I was sent this yesterday by one of our valuable contributing members.  It shows a couple of old Altec 436B units I was converting to RS.124, this would be about 12 years ago.

On these particular units, everything but the back chassis, audio transformers, meter, and chrome front panel light cover was replaced - mostly for the sake of reliability and matching.
The inside shots don't show completed units as, first off, there are no output attenuators yet.  There's also some wiring not yet run.  And 2 screws which hold down the new power supply board are not there yet.

The new supply, besides the H.T., had 7.5V AC to allow for regulated DC on the heaters.  It also has a 24V relay supply and transistor switch for the "Hold" function.  The relay is a socket mount type on the rear, and the transistor base to switch it is connected to a spare terminal tag on the rear.

Front panel shown is the original Altec panel that has been stripped, holes added, painted, then engraved.  The "Dymo"  label for Balance is a nod to the Abbey Road originals which were the same.

I gave them an "unofficial" EMI 1961 serial number since I wasn't aware of any originals from that year.  Pretty obvious these aren't original Abbey Road units though, and they were built for a colleague so EMI lawyers can sit back down please.  ;)

Link below:
 

Winston OBoogie

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New link of pic thanks to Doug, much appreciated  :)

https://live.staticflickr.com/65535/51037634746_3d661440f1_o.jpg
 

Winston OBoogie

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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  :D

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.
 

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emrr

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Winston O'Boogie said:
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  :D

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!
 

Winston OBoogie

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EmRR said:
Now we need some original internal shots!

I know.
My photo backups are long gone so any shots come from trawling old emails for me sending to myself as a secondary backup, or if I sent them elsewhere.  Or someone like you finds an old shot of my conversion  online  ;)

I did have original internals and if/when I find them I'll post.

 

Winston OBoogie

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

It is. 
Until someone opens the front and sees that the big green 10K resistor and the big black 10uF Solen cap aren't bent at a perfect perpendicular!


Haha  :D
 

Winston OBoogie

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

I can testify that booby trap capacitors work like a charm.

Most places I worked, my bench area was (still is) messy and there might be a rat's nest of a prototype in the middle.  But I knew exactly how I'd left stuff before I went home.

If I saw next day that anything had moved because someone in manufacturing had borrowed a screwdriver or something, I'd start leaving caps charged to healthy but not lethal voltages in strategic places.

It was funny to come in and see one of those caps missing.
You almost aways would find it on the other side of the room where it had been instictively flung by whoever picked it up to grab the screwdriver underneath.

HA! I don't know who you are, but I got ya!
 

PermO

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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
 

Winston OBoogie

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PermO said:
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

Fucking brilliant!  Hahahaha

How long until he figured it out?
 

emrr

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Winston O'Boogie said:
I gave them an "unofficial" EMI 1961 serial number since I wasn't aware of any originals from that year.

Looking around, I see some other replicas with 1965 serial #s.  What's the logic to the A/B/C at the end of the serial #? 

What color would you call that paint?
 

Winston OBoogie

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EmRR said:
Looking around, I see some other replicas with 1965 serial #s.  What's the logic to the A/B/C at the end of the serial #? 

What color would you call that paint?

The serial numbers were, as you noticed, first the year, then the batch or build number, and the letter at the end was the actual individual identification.  So each unit in a batch would be: A, B, C... etc

I'll have to look for the actual paint colour I used but it was the nearest RAL I could find to the original's typical British drab gray of the '50's, '60's. 
First ones I had done were stripped, then 'orange peel free please' powder coated with undercoat first  by my regular guy and sent to front panel express as was the other stuff I built (that stuff being flat aluminum panels).  But they can't/won't engrave steel so I looked around and, eventually, a good place in Canada did them.  After that, I just sent them the old panels and they took care of it all: strip, extra holes added, paint, pantograph engrave and infill.

I'd try and save 'em up (old panels) as there's a minimum paint charge etc. So, sending, say, 6 panels, they'd be about $150 each all in.  Which, for what was involved, was a good price.

Tried a place in L.A. once and they totally f'ed up 3 old panels so, wasn't going there again.

 

 

Winston OBoogie

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P.S. After everything at EMI switched over from being green, the original paint identification for panels, including RS.124, REDD.47, desk tops etc. was:

MTS 884/1162 Pol. Finish Light Grey Cell. Enam

But I've never been able to identify that number so, maybe it was an internal one?
 

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