EMI RS124

[rock soderstrom]

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.

It's true, for my planned build I'm strongly oriented towards the original. Nevertheless, I'm also looking at what other solutions and mods are available, and I might even build a heavily modified version afterwards. The Nu vario mu does the balanceing in a similar way as the Culture Phoenix. Are the schematics available for the Phoenix online?

 

[beatnik]

I've found here on the forum schematics for the Chiswick Reach VK-1 which is basically the predecessor to the Phoenix. If you can't find them let me know and I will post them.

 

[rock soderstrom]

I've found here on the forum schematics for the Chiswick Reach VK-1 which is basically the predecessor to the Phoenix. If you can't find them let me know and I will post them.

I found the schematic, thanks for the tip. It's actually very similar to the Nu Varimu.

 

[Rob Flinn]

It's true, for my planned build I'm strongly oriented towards the original. Nevertheless, I'm also looking at what other solutions and mods are available, and I might even build a heavily modified version afterwards. The Nu vario mu does the balanceing in a similar way as the Culture Phoenix. Are the schematics available for the Phoenix online?

I built two RS124. & converted a pair of Altec 438's for a friend. In my view they sound great & I do not have any issues with balance etc The trimmer that is in the EMI design is sufficient to stop them thumping. I didn't find the need to fix something that wasn't broken in the first place.

When you press the trim button to remvove the click from the oscillator it never completely gets rid of the click on my boxes, I just turn it to minimum level, but it's not a problem

The only thing I would recommend is to buy a few 6bc8 or ECC189 to select from.

 

[rock soderstrom]

I built two RS124. & converted a pair of Altec 438's for a friend. In my view they sound great & I do not have any issues with balance etc The trimmer that is in the EMI design is sufficient to stop them thumping. I didn't find the need to fix something that wasn't broken in the first place.

You are one of the voices that make me build according to the original circuit diagram first. The two variants mentioned use different tubes, maybe that's why the use additional trimmers.

The only thing I would recommend is to buy a few 6bc8 or ECC189 to select from.

I bought 2 sets of 4x ECC189. NOS NIB. Plus a few tasty 6CG7s, that should do the trick.

 

[Rob Flinn]

You are one of the voices that make me build according to the original circuit diagram first. The two variants mentioned use different tubes, maybe that's why the use additional trimmers.

That is one reason to build point to point. You can build as standard & then modify if you decide you need to without having to hack the pcb to bits.

 

[rock soderstrom]

That is one reason to build point to point. You can build as standard & then modify if you decide you need to without having to hack the pcb to bits.

That's true, P2P is a bit more flexible, but since I make my own boards at home, that's not a real handicap. I can change everything very quickly the way I want it.

My idea is to build original first, then maybe a modified version if I feel like it, just to see what it does.

I'm collecting a few ideas for this.