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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Also some files are djvu so you need djvu 15568a to open them. Share This Page Tweet. The difference in bias voltage between the 2 schematics remains a mystery. Az erosito reszet elegge macera szetszedni egyszer korabban mar nekiestemugyhogy ezert merult fel a kerdes, hogy a fentiek alapjan erdemes-e vele me’g tokoreszni, vagy kuka.

In any event, you certainly have a good handle on what’s needed here to answer the bias atec. Since Altec used the same output xfmr in both units, it apparently isn’t of much concern. Didn’t have time to study the schematics, but a quick glance suggests that your interpretation is correct.

Tube DIY Asylum

One thing I have noticed is there are two versions of factory released schematics running around the web that appear to be identical except for one has a volt bias level and the other has a volt bias level. It would have been helpful if they printed a serial range for each one, and even more helpful if they specified the plate voltages of the el34s. There are some nice articles online which show how to interpret deviations in the waveform appearance and form some correlation with distortion.


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

Is this a good assumption? Considering that tube characteristics can change quite a bit as they age, a 7 volt bias variation could occur with normal use over time.

In alttec, some files are archived, so you need WinZip or WinRar to open that files. 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 could try converting it to straight Williamson. You need to be a member in order to leave a comment.

Share this post Link to post Share on other sites. Register a new account. These Altec amps were used in the finest movie theatres for multi-channel reproduction of Cinemascope magnetic soundtracks. Do you already have an account?

Wltec 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? As a matter of fact I do have a dual trace rather slow at 15Mhz but not a problem for audio stuff scope, also have two 8 ohm watt Dale power resistors, signal generator for both sine alrec square, variac, Audio Control SA RTA, various Fluke multi-meters Discussion in ‘ Tube Audio ‘ started by ke4mclAug 2, With this, however, I wouldn’t go beyond about 1 watt output keep your multimeter, set to an AC range, across the alteec load to monitor the voltage- keep it to 2.

Sounds like you want to have some “fun” with this! You 15568a won’t hurt anything by running the tubes at a lower plate current. Both appear to be unaltered printings on Altec released manuals and other than this one change they appear identical. I suspect that you’re not going to see a huge difference.


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

PhototoneAug 3, If you have, or can borrow, a copy of the Radiotron Designer’s Handbook it will give you everything you need to graph virtually anything. However, one can make some circuit changes in the interest of better sound. Instead, contact your nearest service center!

The 1568w thing I can see would happen by changing the setting to volts would do would decrease the idle current through the Altex and probably increase tube life, however, would lowering the plate current in this manor change the sound that much as well? It might be a fun experiment! You would then need to measure the transformer impedance easy to do with your signal generator to see which provides the closest match. I agree with the low signal when feeding the input square waves as I wouldn’t want to fry the trannies or pwr sply.

It certainly is possible that they decided, at a later date, to run the tubes cooler to increase longevity. Of course, don’t leave it running like that for too long. The amps I have were set at very close to volts bias and wltec fine at this setting and sound absolutely astounding.