EMI RS124

[thomasdf]

Here is what I have, I am not 100% sure it is an original one, despite what claims the seller. Solen caps and all ... ?
From the looks of it , only the 5th one from the back is a real unit... So no 100% reliable gut shot, I am sorry

 

[rock soderstrom]

Here is what I have, I am not 100% sure it is an original one, despite what claims the seller. Solen caps and all ... ?
From the looks of it , only the 5th one from the back is a real unit... So no 100% reliable gut shot, I am sorry

Thanks anyway! I think you're right, this is a replica or a total rebuild of an old device (Altec 436?). The components are definitely too new for the actual age.

 

[thomasdf]

There are some info and pictures in this thread, mostly of the same build ... a replica made by someone in the US, with some values hidden on some components : https://groupdiy.com/threads/feeler-altec-abbey-road-rs-124-build.41663/page-2

 

[rock soderstrom]

There are some info and pictures in this thread, mostly of the same build ... a replica made by someone in the US, with some values hidden on some components : https://groupdiy.com/threads/feeler-altec-abbey-road-rs-124-build.41663/page-2

It's crazy when you read it from today's perspective.

 

[heatwalk]

Were the originals just a new front panel but kept the existing altec chassis? The altec layout PTP is pretty simple since so few parts to follow if you take a minute to follow the components inside.

 

[rock soderstrom]

Here a gut shot from another John Hinson replica from a Reverb ad.


from

https://reverb.com/es/item/65411415-altec-emi-rs124-rare-abbey-road-tube-compressor

 

[rock soderstrom]

Were the originals just a new front panel but kept the existing altec chassis?

Allegedly the interior was completely rebuilt, but I have only read that on the WWW. I expect the RS124 to have more European components, perhaps Mullard Mustard caps?? Photos could show that...

 

[heatwalk]

Ah. Curious what would have demanded a complete rebuild vs adding to existing. Additions like the feedback 100ks wouldn't require additional lugs to solder in. Maybe the techs wanted to beef up their billable hours…

A period build would be pretty rad but all the .02/400 mustard caps in the world are sitting in Marshalls / marshall clones these days

 

[rock soderstrom]

A period build would be pretty rad but all the .02/400 mustard caps in the world are sitting in Marshalls / marshall clones these days

I've found some for a good price!

https://reverb.com/de/item/46117715...-mullard-mustard-capacitors-marshall-lead-set

Joking aside, I actually still have very few

 

[thomasdf]

I decided to go with the usual suspects in my builds : Nichiden, JJ as well as some TAD and some vintage Cornell Dubilier from my stash. Even a 1:1 period correct clone would not make me write / sound like Paperback Writer so ...

 

[rock soderstrom]

I decided to go with the usual suspects in my builds : Nichiden, JJ as well as some TAD and some vintage Cornell Dubilier from my stash. Even a 1:1 period correct clone would not make me write / sound like Paperback Writer so ...

I will use Mallory M150 for my first build for the 0.022uf positions. "They" use it in their 4k replica as well:

 

[rock soderstrom]

I have a question regarding the size of the required resistors in the main part of the circuit (i.e. not in the PSU).

From my point of view, I should be able to get by with 0.6 watt resistors everywhere.

But I see on photos of the official RS124 replica also 2 Watt types, for example in position R7 at the common cathode of the 6CG7.

Why?

If I use the values given in the schematic I get 46mW thermal load.

The 100k feedback resistors are also 2 Watt types. Do you really need that?

What is your experience on this topic? I'm almost done with my PCB design (I'm really slow) and just checking all footprints to see if they are big enough.

 

[Rob Flinn]

I have a question regarding the size of the required resistors in the main part of the circuit (i.e. not in the PSU).

From my point of view, I should be able to get by with 0.6 watt resistors everywhere.

But I see on photos of the official RS124 replica also 2 Watt types, for example in position R7 at the common cathode of the 6CG7.

Why?

If I use the values given in the schematic I get 46mW thermal load.

The 100k feedback resistors are also 2 Watt types. Do you really need that?

What is your experience on this topic? I'm almost done with my PCB design (I'm really slow) and just checking all footprints to see if they are big enough.

When I make this stuff point to point I always use at least 1W resistors, because they are more robust for the construction. Then you're making a pcb so you might not be worried. The RS124 is so simple I just went P2P.

 

[beatnik]

Perhaps the higher power rating on the cathode bias resistor is to be a bit safer in case of a fault with the output tube ?
A 2W resistor won't burn so fast and then damage the PCB as well.
Could an open circuit cathode bias resistor cause some collateral damage ?

 

[eskimo]

Were the originals just a new front panel but kept the existing altec chassis? The altec layout PTP is pretty simple since so few parts to follow if you take a minute to follow the components inside.

Allegedly the interior was completely rebuilt, but I have only read that on the WWW. I expect the RS124 to have more European components, perhaps Mullard Mustard caps?? Photos could show that...

The "Recording the Beatles book" claims they're 436B:s bought in '59 with:

• New panel (though looking at the thing, I'd assume it's a repainted and engraved 436B, since all the holes are in the right places or added, so I don't see the point in cutting one from scratch as they claim...)
• New mains transformer
• New input level (stepped 200 ohm)
• Added output attenuator. (stepped 200 ohm)
• Added Recovery controls.
• Valve substitutions (reduced noise and created a "harder" sound)
• Added balanced circuit.

Then they throw in "numerous resistor and capacitor changes; new wiring and circuit layout; even changes to the valve sockets themselves". So you could argue it's "completely rebuilt", but I read it as still being the original altec case, original transformers and several other components.

 

[rock soderstrom]

When I make this stuff point to point I always use at least 1W resistors, because they are more robust for the construction. Then you're making a pcb so you might not be worried. The RS124 is so simple I just went P2P.

+1. Yes, I always use bigger resistors for P2P because the thicker wire simply suits this type of construction better.

Perhaps the higher power rating on the cathode bias resistor is to be a bit safer in case of a fault with the output tube ?
A 2W resistor won't burn so fast and then damage the PCB as well.
Could an open circuit cathode bias resistor cause some collateral damage ?

That's an interesting point, I'll have to think about it.

Would it actually make more sense to give each of the two 6CG7 cathodes its own matched resistor?

The "Recording the Beatles book" claims they're 436B:s bought in '59 with:

• New panel (though looking at the thing, I'd assume it's a repainted and engraved 436B, since all the holes are in the right places or added, so I don't see the point in cutting one from scratch as they claim...)
• New mains transformer
• New input level (stepped 200 ohm)
• Added output attenuator. (stepped 200 ohm)
• Added Recovery controls.
• Valve substitutions (reduced noise and created a "harder" sound)
• Added balanced circuit.

Then they throw in "numerous resistor and capacitor changes; new wiring and circuit layout; even changes to the valve sockets themselves". So you could argue it's "completely rebuilt", but I read it as still being the original altec case, original transformers and several other components.

Thanks eskimo for info!

Is there any information about a new edition of this book? I remember when it came out, I thought, wait a little longer, it'll be cheaper and then I'll buy it...I've always been good at financial predictions!

 

[Rob Flinn]

Perhaps the higher power rating on the cathode bias resistor is to be a bit safer in case of a fault with the output tube ?
A 2W resistor won't burn so fast and then damage the PCB as well.
Could an open circuit cathode bias resistor cause some collateral damage ?

I have found that the anode resistors can fail and always use at least 1W. I never us carbon film in the anode either. I have had them fail there even if they are 1W cf. I was fixing some Summit audio compressors the other year and both had 1W cf that had failed in the anode position.

 

[beatnik]

Would it actually make more sense to give each of the two 6CG7 cathodes its own matched resistor?

I'm not sure.
The Thermionic Culture Phoenix that is also based on the 436 has a 2W potentiometer shared between the two cathodes of the output tube and it's used to fine tune the balance, along with another trimpot in the plate circuit of the input vari mu tube.
Perhaps the original 436 /RS124 balance arrangement actually has room for improvement but you probably wouldn't care about that if you are looking to build an exact copy of the original.

 

[eskimo]

Is there any information about a new edition of this book? I remember when it came out, I thought, wait a little longer, it'll be cheaper and then I'll buy it...I've always been good at financial predictions!

Looks like it... https://www.curvebenderpublishing.com/faq

 

[rock soderstrom]

Looks like it... https://www.curvebenderpublishing.com/faq

Unfortunately, this has been on the website for about 10 years - you get the impression that the second edition will be released soon, but nothing happens.