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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Amplifier 1568A

There are some nice articles online which show how to interpret deviations in the waveform appearance and form some correlation with distortion. Please, do not make a copy of the downloaded manual and do not offer to sell it, just use personally to repair defective appliance! Most users of tube equipment, unless they’re really alteec the technical side, never check tube bias 1568z.

I understand that if I were to run the bias voltage to volts it would lower the plate current but what effect on sound quality and output capacity would result in this change is a mystery to me. As far as output power, measure it at 1 kHz at the onset of clipping on the altce and compare with the two bias values.

My basic knowledge tells me that if the amp performs well, output tubes arent running at too high a plate current 1568aa the amp sounds great at the higher vdc bias plate current, go with that.


Register a new account. Your last name is definitely a credit to your interest in the subject!!!

Sounds like you want to have some “fun” with this! If you are not familiar with electronics, do not attempt to repair! To sum it up: My major concern is why Altec printed two schematics with two very different bias levels and what they thought was correct.

Share This Page Tweet. These Altec amps altef used in the finest movie theatres for multi-channel reproduction of Cinemascope magnetic soundtracks. You must log in or sign up to reply here.

Both appear to be unaltered printings on Altec released manuals and other than this one change they appear identical. Any comments would greatly be appreciated.

I recently purchased a pair of Altec A EL34 based mono tube amps. The difference in bias voltage between the 2 schematics remains a mystery. Also some 15668a are djvu so you need djvu viewer to open them.

A guy named Tom Tutay does mods for them. Again, check out the online articles on that- it’s much easier to explain with pix than in words. You could always 1568s a ‘scope on the output with a proper alec connected and see what effect the altered bias has As such, they are designed with certain technical features that would make them immune to most of the common mistakes a non technical operator might make such as running them with no load.

Discussion in ‘ Tube Audio ‘ started by ke4mclAug 2, The basic circuit topology is very similar to a standard Williamson, so as a first draft you could try converting it to straight Williamson. They work excellent and I plan on keeping them all original as they just have too much vintage appeal to change them. With this, however, I wouldn’t go beyond about 1 watt output keep your multimeter, set to an AC range, across the dummy load to monitor the voltage- keep it to 2.


It certainly is possible that they decided, at a later date, to run the tubes cooler to increase longevity.

Altec A Amplifier | karltonkrill | Flickr

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?

Wltec for other manual? The power supply is good, but could use a choke and good caps. PhototoneAug 2, Instead, contact your nearest service center! By chance, is your ‘scope a dual trace type with which you can superimpose the waveforms? 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.

Through Altec Voice of the Theatre speakers, of course. You could suffer a fatal electrical shock!

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 1568q has a volt bias level and the other has a volt bias level.