EMI RS124

[ed rees]

Hi,
Anyone have any RS124 info? I think I've got it all figured out with correct information. I'd love to see a copy of John Hinson's removed RS124 web page, if anyone saved it. I'm trying to get an internal pic of a Hinson unit to check against, also...

Not sure how soon, but I'm going to build one, then post a build thread and schematics, layouts, etc... here. Then you guys can help me weed out any mistakes, or make some improvements to the design! Or if someone then wants to PCB it, I'm all for it.

NEVERMIND: My work here is no longer necessary. 

[pucho812]

why don't you start with what information you think is correct...

[eskimo]

I suppose the question is wether or not you've gotten the correct info, which I suppose you know, since if you have, you musn't be far from the source, ie, and old emi tech or someone who has reverse engineered one. I haven't at least seen anything floating around on the web over the years.

[ed rees]

So far I have: A list of the correct tubes, Rotheu's neon bulb balance circuit, common VK1 schematics (which are quite obviously a close RS124 derivative), real RS124 response curves, and lots of text info I've gotten from people "in the know".

I feel we should be able to get it really close with all this, atleast a very good 'poor mans' RS124.

[pucho812]

fwiw if the rs124 sounds anything like the plug in, you can have it... I found it way to heavy in a bad way, well bad to my tastes.

[ed rees]

Yeah they definitely have lots of color. Some people love it, some hate it. Not much of a multi-tasker, for sure.

I like the plugin, I'm willing to risk several hundred dollars to see how I like a real(ish) one.

[rotheu]

Here we go!!! Nice sound, especially on the bass, but release times are way to slow IMHO. The key to stability and solving the problem with thumbs original Altec 436B had is those two 39K plate to plate feedback resistors, the rest is nothing special.

[ed rees]

Here we go indeed!    Ordering my parts tomorrow... and starting on my chassis.

[DaveP]

Hi,

I made one of these earlier in the year, I put in an extra tube to cure the stability problem and my own balance circuit, I didn't find the neon necessary but I had to select a balanced 6BC8 to get it right (had to buy 10 to find one).  By using a regulated supply from the UA175 you can extend the compression ratios obtainable up to 8:1, easily selectable as in my schematic.

[strangeandbouncy]

HI,



  that looks very interesting. What tube is V4?


  Kindest regards,


   ANdyP

[DaveP]

Hi Andy,

Tube Line-up
V1  6BC8
V2  ECC82
V3  6CG7
V4  6AL5
V5  OB2

[mich]

Great work here!

something i did to the same circuit with great results: adding an intersatge transformer.
with it,i could bring down the SC cap to 0.22uF with 150k release and 18k attack resistors.
very fast release without stability problems.built a few of these and love what they do.

[MrZpliff]

This is interresting. Looks like a nice P2P-project.

Mich: Where did you add the interstage trasnf ? and what ratio/impedances.

[ed rees]

Cool design too, Mich! Is that a real Altec meter, or a re-purposed Jewell MM2? Funny, they still make that same old meter.

[MagnetoSound]

@rotheu, what is the origin of this schematic? Is it simply your own variation on a theme, or did it come from someone "in the know"?

[eskimo]

Arr, screw you guys! I'd totally shelved all varimu plans!  

[eskimo]

Quick, buy all my 6BC8, 6CG7 and 6AL5's please!

[eskimo]

This is interresting. Looks like a nice P2P-project.

Mich: Where did you add the interstage trasnf ? and what ratio/impedances.

I'm guessing right after the 6bc8..

[mich]

The interstage goes between the first and second stage (replacing the .022uF coupling caps)

i used a military utc that i had 1K:4.5K(1:2.12 turns ratio) with lots of henrys...and  zobel network on the output to flaten the response.

you can try anything you have on hand - the bigger core the better - and more inductance gives you more low end(simplifying..)

[rotheu]

@rotheu, what is the origin of this schematic? Is it simply your own variation on a theme, or did it come from someone "in the know"?

Someone "in the know"