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Reed,
The symptoms you have is most likely capacitors. As the amp is operated the old capacitors start to reformand repair themselves, that's why the amp is improving.
I striongly recommend you replace all of the electrolytic capacitors, including the main power supply ones which probably caused the switch on thump. If it were me I would not be using an amp in this state. One of those caps could short at anytime and take out many other components in the amp as well as your speakers.
from the numbers you post i believe you have one of the later versions------but i'll check to be sure---------the amp should be very quiet if wired correctly------how much noise does it make if the inpur wires are disconnected??????------if the amp is quiet with no wires connected its not the amps fault but the driving component or the way it is interfaced-------are you using the XLR's or the 1/4 inch inputs???????---------for use in a stereo i strongly reccomend using the 1/4 inch inputs and removing the input transformers if they are installed---------personally i wouldn't worry about damaging the speakers as the 9440 has a lot better speaker protection sensing circuits than most HI-fi amps------the DC latch circuit is really fast and works with a really fast magnetic blowout relay-------when you hear the pop is it when you first turn the power on or is it several seconds later when the relay clicks-------there should be no noise at power up since the speakers should be internally disconnected till the relay closes 5 to 7 seconds after turn on-----if the pop occurs when the relay closes the problem is drift in the DC offset adjustment--------measure the speaker terminals with the speaker disconnected-----if there is more than 10 or 20 millivolts it is out of adjustment------ the cap i mentioned has some effect on that adjustment so wait till i check for the number--------i have about a dozen 9440's as well as a HP bridge--------rarely do i find a bad supply cap in these amps so i wouldn't worry too much about them--------and most of the other caps seem to age well except for the one cap i mentioned-------i'll check this weekend when i look about your revision number.......RC
reed-------from what i can see you have a very late version-----the driver board is the one with all the changes and anything after 5 is pretty good-----it looks like you have version 11-----i didn't even know they got that high-------as for the cap its C-3------the parts are clearly marked on the boards on versions after 3 or 4--------as i have said i have many of these amps and in all of them this cap has needed replacing-------when its value is low the low end really falls off-------its supposed to be 50uf/16v-------i have taken them out of amps and some of them have been in the 5uf range------and it doesn't seem to matter what kind of service tha amp has seen-------they just seem to go bad for whatever reason-----perhaps it was a poor choice of vendor cause the application doesn't seem too unusual-------i have only had to replace the main power electrolytics in two of my amps so with your late version i doubt you have to worry about it............RC
Thank you for all of the information Richard. I have the caps ordered. I will post the results when I have them changed. Reed G. Hinton
I have several of the Altec 9440-A amps, and one of them has the same issue, only with just one channel. The amp will go into oscillation sometimes and peg the one meter. I have changed out all the caps on the boards, but it still does it periodically. Any more hints? I do have the schematics and service manuals for the amp, but am only a novice at repairing them.
Thanks in advance for any help!
My amplifier was really unstable. If I would tap around inside the amplifier with a wooden stick the sound would come and go. I finally fixed the problem. I noticed that when I had the top off of the amplifier that there was sparks at the screw terminal of one of the big 9800 uF aluminum electrolytic capacitors when I turned the amplifier on. The sparks were between the terminal of the capacitor and the terminal, with wires, that was screwed to the capacitor. I thought that was strange because they are touching. I removed the screws for the back heat sink assembly and laid it back to gain access to the big capacitors. I removed both big capacitors and noticed that 3 of the connections had "internal star" lock washers between the terminal with the wires and the terminal on the capacitor. The forth one did not and the connecting area between the terminal with wires and the terminal of the capacitor were both black. I sanded both and put a new "internal star" lock washer between and screwed the connection down tight. I put everything back together and the amplifier is now really stable. My problem was common to both channels which makes since because it was a common power supply problem. I would really check all of the connections on your problem channel. Could be a loose or dirty one. Good Luck! Reed G. Hinton
I got the new C3 50 uF 16 V capacitors for the driver boards today. These are the ones in the feedback circuit. I replaced them and the amplifier sound is really clean now. Reed G. Hinton