Altec valve compressors at EMI.

[Dick.1]

More specifically the Altec 436 range

One of my friends is recording early guitar based instrumentals (Mainly Shadows etc....) & is a member in a forum that looks at & discusses music like this that I mod on.

He has pro standard recording gear (Mackie) & a load of toys in his studio but like most of us he was always looking for that extra "something" in his recordings that is missing when trying to re-create 60 yr old recordings

He recently imported an Altec 436 © that is mainly original apart from some "safety" work that had been done mainly replacing caps & a few resistors

This thing comes with a fixed (50ms) attack speed that appears to be controlled by a 1uf axial cap

In his quest for a faster response time the obvious solution (to me at least) was to change this cap to 0.47 value which did indeed reduce the the delay down to 25ms ( these speeds are measured by scope)

Ideally he wants to get down to 10ms (for musical reasons).......... but trying a 0.22uf cap just sent things into distortion as the cct tried to cope with this change acting a bit like a noise gate switching in and out.

I live in Durham & Phil lives in Wales so it's a bit of a chess game by pms etc... (more so as Phil has no direct electrical experience but is a good engineer who can follow suggestions etc...without any issues)

After all this waffle....my question is

Does anyone have any experience/knowledge of these machines ?

I've looked around quite a bit but can't even find a cct diagram for the EMI version of these that people agree is accurate

Why EMI ?

Around 1960 EMI bought some of these (436b model) & modified them to suit there recording purposes & these ones were designated RS124 & used up until around 1964 until they bought in Fairchild units

The EMI version of these Altecs is now part of the legend that is the "Abbey Road" sound

I do have a good cct for the 436c if anybody wishes to have a look

Anybody any ideas suggestions ?


Dick.

[Dick.1]

How can I delete this thread please ?

Dick.

[Mark Hennessy]

I can delete it, but why?

Would closing it be sufficient?

[Dick.1]

There's been no interest shown in the thread Mark

Not sure how to close the thread off come to think of it either, but closing it will work also if you can do that.

Thanks

Dick.

[Mark Hennessy]

Closing or deleting threads is a job for Administrators and Moderators. That's why you don't see any options to do either.

In this instance, I don't really see the problem. You never know; someone might chip in later, or at least be interested in how it went.

I'll close it if you feel really strongly about it, but on this forum, closing or deleting threads is a rare occurrence. I appreciate that some forums might do it differently.

Hope this helps,

Mark

[Dick.1]

Fair comment Mark

I'll let it ride for now, maybe our exchange may trigger some interest

Things have stalled at the moment as I'm finding it very difficult to find a "real" RS124 cct to see how they adjust the attack times

At the moment the attack time is down to around 16ms after playing around with some caps & "padding " resistors & is working more or less OK at the faster speed


Dick.

[Refugee]

If we can have some circuit diagrams perhaps some of the circuitry might be usable as a replacement for those unobtanium thermistors in signal generators.
Lets see...

[Dick.1]

If we can have some circuit diagrams perhaps some of the circuitry might be usable as a replacement for those unobtanium thermistors in signal generators.
Lets see...

OK, I give in....what are you talking about 


Dick.

[Refugee]

I was thinking of the AGC circuits in signal generators that use a therminsor to shunt the feedback to regulate the amplitude. I was wondering if the bit of circuitry that detects the spikes and uses the signal might be useful as a replacement for the thermistor in a signal generator.

[Dick.1]

I didn't make the connection with SG's but can see how their could be some interest if as (I think) your looking for a cct diagram

This is what I'm looking at with the object of reducing the original "attack speed" of 50ms to as close to 15ms as possible

http://www.dvq.com/hifi/images/436c.pdf


Dick.