ALtec 9440A... suggestions?

[Stormrider]

I picked this amp up cheap at a tag sale (really cheap) not to long ago. It has problems as the thing is about 40 years old. Both channels have a mains hum, and channel two is pretty flaky. Sometimes it will work, sometimes it won't. Now, because the amp is so old, i think i have only a couple of options.

1) Rebuild the amp, replacing cracked wiring and all the electrolytics, and other components. Remounting the output transistors with new insulators and thermal compound etc... This amp is very complex and difficult to work on, so i don't know if it would be worth the time/effort.

2) Tear everything out except the transformer and build a new amp into the chassis. This would be the most expensive of course, but possibly the better option. As far as i can tell, the power supply has +/-43vdc rails and an aux +/-18vdc. By looking at the schematic it seems to me both of these rails were filtered through the main caps, making it +/-61vdc. I'm not sure of this however so any help there would be appreciated. This is a 200/400w amp at 8/4 ohms so, i would have thought the voltage should be higher. The transformer is huge, around 1000va.

I have included a link to a zip file listing of the Altec amps. Please scroll down and take a look at the 9440 file.

Thank you for any assistance.

http://alteclansingunofficial.nlenet...ers/index.html

[Bigred]

Looks like its 81v rails and 43v rails (high and low power modes, They both get filtered through the same caps but they don't combine its either or). I have never seen an Altec amp before or much less heard one. It looks like a beauty though and I love the older stuff so personally I'd rebuild/repair it. It definitely needs caps. If the channel is intermitent I can't see it being a major fix (solder joints/connects).

[Stormrider]

I must be dyslexic. That is 81vdc. Thanks for the help.

So...

Rebuild = 1
Renew= 0

[Original Burnedfingers]

Do NOT junk this amplifier or attempt to build some type of inferior piece of junk in its chassis.

This is an extremely good sounding amplifier when it has been gone thru and is working correctly.

I have had about ten of them in the last 15 yrs and wish I had saved several of them.

picked this amp up cheap at a tag sale (really cheap) not to long ago. It has problems as the thing is about 40 years old. Both channels have a mains hum, and channel two is pretty flaky. Sometimes it will work, sometimes it won't. Now, because the amp is so old, i think i have only a couple of options.

Clean the input contral as well as the bridge,100%/40% switch as this is a common problrm with them.

In addition to the cleaning replace the filter caps as they are very old and a common problem for this amplifier.

[Stormrider]

I have gone through and cleaned the controls with cleaner. I will order some 10kuf/100v caps as soon as i can. I don't suppose you have a source to get some of a similar size so i don't have to change the mounting brackets?

I will look again and see if i can find the prblem with the 2nd channel.

Thanks for your help guys.

[Original Burnedfingers]

Check out Apex Jr for new caps.

[djk]

Love the 9440.

Do not plug the boad edge connectors in wrong! Being off one pin will cause flames to shoot out of the board behind the front panel, as well as the channel you're working on.

In addition to the main filter caps, replace the input coupling cap (C1) and tack a 0.1µF film type in parallel. Do the same with the cap in the feedback loop (C3).

Increase C10 and C11 to 22µF, use 160V rated caps if they fit.

Suck all the solder out of the two sets of pins on the edge of the amp driver boards. Re-solder with 4% silver solder (original pins are gold and the solder joints fracture).

Don't mess with anything on the heatsink (unless it's fried).

22.000 Mfd 100V 2 1/2" Dia X 4" Tall + 1/8" w/screws new stock made by Hitachi $15.00ea

http://www.apexjr.com/new.htm

[Stormrider]

Thanks for the suggestions djk. I will do these upgrades.

I saw the hitachi's at apexjr, and those look like the best deal around. I'll order up a pair when funds permit.

Keep the suggestions coming guys!

[Stormrider]

I took the old, original power supply caps into my shop today to test them on the benchtop Sencore meter. They were definetly bad, and not working. So, that explains the hum on both channels.

On the driver boards i replaced the small electrolytics with new ones, and some of the disc caps with film types. I am about to do the same for the control board as well. I still need to order the 22uf/160v parts and the main filter caps.

[Bigred]

Excellent AJ! I'm glad to see you took the advice and decided to breath new life into the beast. Keep us updated with your progress.