Altec 250su any experiences

[bieckmusic]

Hi,

I recently discovered an Altec 250su in an old abandoned church.  It's a 10 channel stereo tube console.  I bought it for use in my studio.  Anyone have any experience with one.  I did not even fire it up yet, since it hasen't been used since the early 70s I am afraid of blowing something up.  Until I at least check the powersupply voltages, etc...

I imagine I'll need to replace lots of caps and there will be some issues that crop up along the way...  though it physically looks like its in perfect shape.

best!
Greg

 

[emrr]

Yes, some, more later.....

Get the documents.

What modules and PSU? 

Don't fire up anything more than individual modules one at a time on a different variable PSU and confirm/repair one at a time before powering the whole thing.  The whole thing at one time would be a form of purposeful insanity, unless you just like standing around with a fire extinguisher. 

 

[bieckmusic]

Ha, absolutely, I told them they weren't allowed to plug it in.  It's ok to check voltages on the powersupply output without having it connected to the console, to make sure that is working? 

The first step is getting it shipped to Nashville.  Just produced a record for someone sponsored by TA, so I think I can get free shipping.  woo-hoo

I won't move any tubes because they probably biased for the individual modules.

It looks exactly like this in this cool little brocure, but I haven't yet confirmed the preamp/lineamp modules and quantity. 

http://www.bayoucables.com/altec/Altec-250SU-Promo-Man.pdf

 

[emrr]

I wouldn't put full power on that PSU without a load, it is meant to eat a lot of current and voltages will be very far off. 

There is no tube biasing; it's cathode bias. 

These consoles were frequently retrofitted with solid state 9475A modules, and the PSU changed to match. 

Assuming you know it's still tube based, there could be anywhere from 5 to 13 amplifier modules and/or a mix of utility trays with bridging transformers. 

These consoles have fairly flimsy metalwork.  If at all possible, it's worth the trip to pick it up.  Otherwise a full crating with heavy internal foam supports, all modules removed and packed separately. 

 

[bieckmusic]

hi Emrr,

here's a photo of the guts.  looks like it has 8 preamp modules and some line imput interfaces??  I can't tell if all of the modules for the mixer are installed, looks like something is missing??

lots of nice tubes and transformers tucked in there....  so pretty 

 

[bieckmusic]

here's a closeup of the 458a modules there are a total of 9

 

[bieckmusic]

there are two 459a modules in the left prog and right prog slots

 

[bieckmusic]

here's the front, it's in pretty nice physical condition.  I haven't bought it yet, just wanted to make sure it was worth the trouble...  open to anyone's opinion.  I have some tube console emulator plug-ins and am not super impressed with those.

I'm looking for some nice tube pre's and a sub-mixer with some nice tube coloration...

Looks like someone removed the center channel amplifiers...  not sure why I would ever use those.

I hear they sound pretty good, VK sold one for around $9k.  I wonder how hard it would be to add direct outs to it, that would be necessary for tracking...hopefully it would interface with my Avid HD I/O properly.

anyway, this seems like a cool project.  Would love to build some RuffRecords helios eq's to go along with this   

thoughts??

 

[ruffrecords]

anyway, this seems like a cool project.  Would love to build some RuffRecords helios eq's to go along with this   

thoughts??

Isn't strange how everything is connected. I am fascinated by old tube mixers. Seeing this thread I downloaded a brochure for this mixer. I was particularly taken by the the heater power supply which creates  13 amps of roughly smoothed 6.3 volts; so much so I tried ac heaters on my Eurochannel mic pre design and it worked extremely well.  One reason I was interested in ac heaters was because it would allow more design flexibility. Someone had asked if it would be possible to do one of my EQ boards with a built in gain make up amp . It only needs one tube and the best one to use only has a 6.3V heater. And here you are thinking of adding my EQ to the mixer that started it all.

Cheers

Ian

 

[bieckmusic]

thanks Ian, things are coming full circle!!  I should have the console here next week... have to say I'm very excited even though it could be months before I hear any audio.


Those peerless transformers look very cool...

best!
Greg

 

[emrr]

Thought is you better hurry up and seal the deal, before it's gone.  Or pass the info on to me!  This is not a time to kick tires unless the asking price is really high.  Ask the hard questions:  can they ohm out all the transformers and confirm they are good?  If not, price should reflect the risk you are assuming.  With that many modules, entirely likely there may be a bad one, and spares are unobtainium.  Amp modules are fairly hard to find at any price if you go looking. 

It probably never came with the center channel amplifiers.  The module count was optional, the tray count was standard.  Reread the info you linked 4 times through. 

Sounds like you will need to pay a knowledgable vintage tube console tech to walk you through the options with this.  It'll be money well spent.  And you need a manual of course!  The audio cyclopedia 2nd ed. has a flow chart. 

 

[ruffrecords]

thanks Ian, things are coming full circle!!  I should have the console here next week... have to say I'm very excited even though it could be months before I hear any audio.


Those peerless transformers look very cool...

best!
Greg

I think you are very lucky. There are no similar consoles in the UK. I am envious!!

Cheers

Ian

 

[coilaudio]

The Altec 250's sound great.  From 60s capital records type hi-fi, to blown out garage rock. I've restored and modded two of these guys. Looks like yours is pretty loaded, even has the tube check meter in the back.

The mix bus uses five amplifiers for two stages of make up gain. L, C, and R each get their own 458 booster amp. The "C"  458 then gets split by a resistive"splitting pad" and sent back to the inputs of the L and R boosters.  The LR boosters then get fed to attenuators and to the 459 program amp. Ridiculous amounts of cool gain staging, a little over 100db to play with.  You need the center 458 to get true LCR mixing, without it it's just LR. Pretty magical hearing a microphone through three tube amplifiers...

The 458mic pres are excellent, super hi-fi, langevin-esque.  Very simple design, only a few electrolytics and resistors in each one to check/replace. The 459s are almost as simple, two caps and some resistors in the signal path, few electrolytics.

Looks like you have a few of the utility trays also, these allow you to bring in line levels devices, necessary if you want to actually "mix" on these. You can find original 15095 transformers and make these. I swap modules on mine all the time...

I would recommend replacing all the electrolytics, in both the modules and the power supply, they weren't meant to last 50 years. Also check all the high voltage wiring across the back, had to totally replace all of it on one of them.

As far as mods, They come with insert points on the back that are jumpered. Points are between the preamp outs and the front davens, ins and outs of the LCR boosters, and ins and outs of the Program amps. You can come right off the insert for direct outs or after the Davens for final gain control.  After the Davens, you have to do it with a terminated switch to keep the the passive mix buss happy.

Two minty restored versions of these recently sold for 26k and 28k respectively...
Good score...

 

[bieckmusic]

thanks so much for the great information.  I will have the console by the end of next week I'm told. 

First off, I need to find a schematic.  Does anyone have one.  The console ad has schematics for the pre amps  but a console and power supply schematic I can't find?

and thanks for the Davens reference.  I looked it up, and what we call a fader they called a Davens knob.  how interesting!! 

 

[ruffrecords]

Here is the PSU schematic:

http://www.benmook.com/tech/documents/Schematics%202/Schematics%201/Altec535Aps.pdf

Cheers

Ian

 

[bieckmusic]

it's here!!  arrived safely...

got the power supply schematic, it's in really nice shape, been locked in church office for 45 years.  now where to begin?  I need to take a look at the power supply, it's got a calibration pot for 6.3 volts.  I'll need that to work properly before anything else can happen...

exciting times,
Greg

 

[coilaudio]

I'll PM you a scan of the original manual. The 6.3 switch is for loading the DC filament supply when the board isn't fully loaded with with modules, the B+ self regulates. I copied this in the power supply for our modular preamps. You can check out some pics of one I restored on our instagram and twitter.

http://instagram.com/coil_audio/
https://twitter.com/coilaudio

Do be careful, there are lethal voltage inside the power supply and console.

 

[bieckmusic]

great, thanks for that!!!

yes, is it ok to power up the powersupply with nothing connected?

 

[coilaudio]

It is OK to power up without any load. Usually a good idea to use an external power supply to slowly reform all the caps if your not going to replace them, or at  least use a variac to bring up the supply slowly.  Failure at lower voltages is better than a massive failure at full/high voltages.

 

[emrr]

Variac or lightbulb limiter method a very good idea.    Monitor those caps for heat during/after re-form too, if they are warm to the touch after being brought up, they should be replaced.