KLUDGE@AGCB1.LARC.NASA.GOV (08/21/90)
I am not sure if I have worked on the 1570, but I have worked on some of the 1500-series model amplifiers and the information may carry over. These are fairly clean but unexciting amplifiers that run pretty hot. They have a bit of a problem with really heavy bass but are overall good amps. Whatever you do, replace the cathode resistors with well-matched units. Replace the grid bias resistors (probably putting pots in there as well) before one of them goes bad and blows the whole thing up. And replace all\ the caps. Make sure the one you are looking at has all the tubes in good shape (check especially for gassiness) and that the transformer has not begun to delaminate. This is a major problem with some of the older Altec amps. These units were designed to drive Voice of the Theatre amps with heavy add-on bass drivers and generally have decent power. Most of them do NOT have 4-ohm tabs, but they have 8 and 16 tabs. Many of them have two seperate windings which are put in series for 16 ohms and with a bit of rewiring you could parallel them for a 4 ohm load. Check the transformer before buying! (Also make sure that it's the original transformer, or one of the Thordarson replacements. The bias resistors will often go on these units, causing the tubes to run red hot and the transformers to burn up, so there are a lot of units out there with transformer problems). There is a balanced input on the models without preamp stages, which goes into an octal socket which would have a transformer (or a preamp) plugged into it. Bypass the socket with a couple of wires which will eliminate two more connections in the audio path, and get an unbalanced input. Overall, they are decent amplifiers. Don't pay more than $100 for one if it needs any amount of work. --scott