Altec 250A Console Restoration Dilema

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Guto P

New member
Joined
Aug 6, 2021
Messages
3
Location
Sao Paulo
Hi, I have an Altec 250A console for restoration. It was of Eldorado Radio Station from Sao Paulo - Brazil since 1958. I am cleaning it and thinking to restore to use like a preamp for analog recording and DAW, but there is a dilema, it is incomplete. It had two outs channels and a lot of high and low levels ins (microphones, lines, utility, air cue). Originally there was for nine plug ins preamps A-428B (seven from factory and two addictional) and three plug ins line amps A-429B.

In A-428B section preamps, there was five for microphones and two for boost (when used as booster the input transformer is connected for 150 ohms). The two boosters is for the mains channels A and B outs. There is a mounting tray to more two additional A-428B to use as microphone preamp. Also there is option to use two external microphone preamp feed through jacks.

In A-429B section, two units is for line amp in the main channels outs A and B (after the two A-428B boosters). The other A-429B unit is for monitor, amplifying talkback microphones and outs to speakers (studio A, studio B and control room). Is the same amplifier for line and monitor, just change the supply voltage to the output. For line mode is reduced 25% (1 watt output) and for monitor mode is full voltage (8 watts output).

But my Altec just had one preamp A-428B and two line amp A-429B. I am thinking in to use the A-428B as microphone preamp and two A-429B as line amp in main channels A and B to mastering Left and Right stereo recording, without monitor section. But the dilema is: “is it possible without the two A-428B used as booster in A and B channels out?”

Another option is to use the A-428B as booster, just for use in one channel out, without stereo and microphone preamp (but will can use two external microphone preamp in jacks). The other radical option is use the three plug ins amps as stand alone (and lossing the 250A Console, without keys, mix, volume control, VUs).

I am posting pictures and copy of block diagram and lower section layout. Thanks a lot to Mike mjrippe for email me the manual and invite me to the GroupDIY. Sorry my mistakes in English. I would like know opinions of the experts. Thanks.

Guto P
 

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Greetings Guto,

As I probably mentioned in our emails, I have never worked on an entire console. I have racked the 428B as a stand-alone preamp and it has plenty of gain. A friend of mine who is a mastering engineer uses a pair of 429B that he can insert in his signal chain. I'm sure that Doug @emrr will have some input here.

Yours,
Mike
 
Yes, thanks, first I intend to keep the Console, I will try to work without the booster amp. I'll try by passing the booster simply without putting the booster amp plugin on mounting tray or maybe making a direct link, a jump if necessary
 
If you won't use the other input channels, you could disconnect much of the mixer network and lessen the mixing loss, which is why there's a booster stage.

The booster and PGM amps are probably unbalanced with one side grounded, confirm from schematics. That's another consideration.

This is such an attractive platform and a great centerpiece. I'd be tempted to build DIY amps for the other slots, since they are standard D-dub connectors. But it depends on what you really want to do. These consoles are impractical for most modern use, but not all. Original amps will be hard to find under $1000 apiece anymore.
 
Thanks for posting Doug. Great tip to desconnect. The mics ins and line ins with transformer is balanced but the mixers section is unbalanced. I dont know what I will do, I will try some options, but probally use the amps as stand alone and let to somebody DIY new plugins amps
 

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