Altec 436C Compressor.

Just looking at getting one of these, looks like a really simple vari-mu unit. Does anyone have any experience with them? Has anyone modded them? Is there anything fun to do with them inside?

If you do a search on the 436c you will turn up quite a bit of info.

I just ran it up, and although it looks like it is out of the box pristine, it sounds like ass. Quite distorted, and when I turn the gain past a certain point it pops and becomes really distorted, and the compression drops right off by about 70%, and it stays that way even when I turn the volume back down. I guess it may have a bad cap or tube, I was wondering whether to buy it, but the only vari-mu I have ever had was an unmodified CBS Audimax II, which wasn't much use. (I did manage to swap it for a nice Studer A80 2 track machine though).

I would like to hear the Altec in it's full glory though, so I will open it up on Monday and see what is amiss. Has anyone tried one on vocals? Where do these things shine?

Like I say do a search on the newsgroup. There are quite a few people who have made these, myself included. It isn`t the cleanest sounding vari mu in the world to begin with.

Assuming the transformers are OK, if you replaced all the components & valves it wouldn`t cost that much. The version I made from surplus parts only cost about £50.

Thanks Rob, did you use the multi type electrolytics in your compressor? I haven't seen these in a long time, particularly with 3 caps in the one can. It would get a bit messy if I had to start putting caps all over the back of it!

I just used single axial types, but then mine was faithful to the circuit diagram but not the layout.

[quote author="Steve Jones"] [...] the multi type electrolytics in your compressor? I haven't seen these in a long time, particularly with 3 caps in the one can. [...] [/quote]

JJ (the tube guys) are making a 40/20/20/20uF cap can again , the usual guitar amp stuff shops probably have them.

HTH
;Matthias

How long did you leave it on? Sometimes if you leave the old tube based stuff on for a few hours the caps reform enought to tell if there is a good sound in the unit.

I believe PRR wrote something like this in the old place.

I have done this with some old guitar amps The problem is you need to watch the unit I like to do this kind of stuff outside away from anything that can catch fire and also if the caps vent or a resistor burn you don't have that smell inside.

thats a bad smell....

436 is a pretty cool one trick pony, mine is in good shape and it distorts like a mother. Its a one trick pony though, full on. You CAN modify these, the EMI compressors were nothing more than modified 436's, not that Im any help with a schematic or anything, but thats the word... A 436 will do a cool thing to a snare drum, if you ever find the occasion to put something like a snare through a tube amp.

dave

Stevo, I have some schematics that may interest you.
email me/ PM me and I'll buzz 'em to ya on Monday.
The Chiswick Reach is the same basic format as the 436 but with some interesting alterations...Not that I have the Schem for one of those you understand :roll:

chef

While were on the subject. Here are some pictures of my 438. The input and output attenuators make this thing a bit more useful. I've used the unmolested versions and found them, pardon the pun, limited. I don't have a schematic or a clue what's going on in there, but it works. I like it.

http://img.photobucket.com/albums/v473/MikoKensington/438a.jpg
http://img.photobucket.com/albums/v473/MikoKensington/438guts.jpg
http://img.photobucket.com/albums/v473/MikoKensington/438inpot.jpg
http://img.photobucket.com/albums/v473/MikoKensington/438out.jpg
http://img.photobucket.com/albums/v473/MikoKensington/438aguts.jpg

Thanks for all the help guys, i am looking forward to getting into it. Thanks too for the pictures Miko, an output attenuator would be really useful, this thing is HOT. It is strapped for 600Ohm output, I wonder if it would be better to set it to 150ohm? I guess that would be getting pretty low for interfacing with modern gear though.

The compression bypass is nice too. I run things through this a lot. I rarely compress most of the time I use it. The amplifier portion is pretty fun on its own.

Using pads are a necessity.

This is such a laugh... The Altec has been to several renowned techs over the years, who have given it back saying it is fixed. The owner always complained that it doesn't sound very good. I got it from him, ran it up and it does sound like I described earlier in the post. Pretty awful. So I undo the 2 screws, flip the front down, shine a flashlight in side, and the first thing I see is that 2 of the wires on one of the big power filter caps HAVE NO SOLDER WHATSOEVER! The wires are from the mains transformer and a link line to the next cap. They are just 1/2 looped around the capacitor terminals, in plain sight. Loose as you like. The other ond of the wire is properly terminated with a blob of green paint, so it was never soldered at the factory.

This unit has been in service for 30 years or so like this, so many techs must have looked at it, it boggles the mind.

:shock:

Quality control?

How does it sound now?

Don't know yet, I will take it into the shop in the morning and cut loose with some solder. I bet it will improve. :green: