GENERAL DESCRIPTION. The A Amplifier is a rack mounted, AC operated power amplifier intended for use in sound reinforcing, paging, music distribution. Hi there, up for sale is a Vintage Altec A Tube Amplifier. It is in EXCELLENT condition and sounds fantastic and works as it should. This would be perfect. i’ve read mixed reviews on these online. some say they arent all that special and basically PA amps. i saw some stuff that claims they are good.

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As far as sound quality with the two bias voltages, why not reset it to and take a listen? Create an account or sign in to comment You need to be a member in order to leave a comment Create an account Sign up for a new 168a in our community.

Altec A Proper Bias Level – Technical/Modifications – The Klipsch Audio Community

If you want to join us and get repairing help please sign in or sign up by completing a simple electrical test or write your question to the Message board without registration. If you have, aptec can borrow, a copy of the Radiotron Designer’s Handbook it will give you everything you need to graph virtually anything. PRMAug 2, Your name or email address: Again, check out the online articles on that- it’s much easier to explain with pix than in words.

Compare that to the appearance of the input signal from your generator. I assume doing this with a dummy load I also have at or near the maximum rated output level of 40 watts at say 1kHz would probably be a good place to start? No, create an account now. To open downloaded files you need acrobat reader or similar pdf reader program.

The basic circuit topology is very similar to a standard Williamson, so as a first draft you alfec try converting it to straight Williamson.


Also, in case you are not familiar with it, check out www. Posted September 19, You would then need to measure the transformer impedance easy to do with your signal generator to see which provides the closest match.

As far as output power, measure it at 1 kHz at the onset of clipping on the ‘scope and compare with the two bias values.

Share This Page Tweet. Considering that tube characteristics can change quite a bit as they age, a 7 volt bias variation could occur with normal use over time. However, one can make some circuit changes in the interest of better sound.

altec a, hifi or PA amp? | Audiokarma Home Audio Stereo Discussion Forums

This, of course, will affect the required load impedance somewhat. These Altec amps 1568x used in the finest movie theatres for multi-channel reproduction of Cinemascope magnetic soundtracks.

It certainly is possible that they decided, at a later date, to run the tubes cooler to increase longevity. PalustrisAug 2, This file is downloadable free of charge: Tubes are all NOS and barely broken in with maybe 50 hours on them.

The chances are, even if it does increase the distortion a bit, you may not even notice a difference when latec music. You could always put a ‘scope on the output with a proper load connected and see what effect the altered bias has To sum it up: Also some files are djvu so you need djvu viewer to open alted.

Both appear to be unaltered printings on Altec released manuals and other than this one change they appear altev. Since Altec used the same output latec in both units, it apparently isn’t of much concern. Fanatic, I do have a scope I could look at the change with.

PhototoneAug 3, There are some nice articles online which show how to interpret deviations in the waveform appearance and form some correlation with distortion. That said, they sound good alted they are. I do have a scope I could look at the change with. But, in any event, you can connect your 8 or 4 ohm resistive altdc assuming it’s rated for the power needed and look at the sine wave appearance at the point just before the onset of visible clipping a flattening of either the top or bottom rounded portion of the waveform.


My major concern is why Altec printed two schematics with two very different bias levels and what they thought was correct.

PRMAug 3, You can write in English language into the forum not only in Hungarian! I agree with the low signal when feeding the input square waves as I wouldn’t want to fry the trannies or pwr sply.

Sziasztok, MX gyel van valakinek tapasztalata? You can try that for multiple frequencies to get some appreciation of what’s happening across the audio band.

Altec 1568A Amplifier

You must log in or sign up to reply here. Do you think they later changed the original bias spec of vdc to in an attempt to make the amp more bullet-proof and have longer tube life, or do you think they first chose volts and then they felt the plate current just needed to be higher for better operation and sound quality so they revised it to volts?

Please post your results after doing the experimentation. The power supply is good, but could use a choke and good caps. Who knows, you may find that the “correct” bias voltage based on the graph is in between the two values printed! Log in or Sign up. You could suffer a fatal electrical shock! They were intended for use in churches, bowling alleys, shopping malls, dance halls, high school auditoriums and, naturally, movie theaters.