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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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Vintage Altec Lansing 1568A Mono Block Tube Amplifier

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 15688a. Log in or Sign up.

As far as sound quality with the two bias alhec, why not reset it to and take a listen? A guy named Tom Tutay does mods for them.

The amps I have were set at very close to volts bias and operate fine at this setting and sound absolutely astounding. As far as output power, measure it at 1 kHz alltec the onset of clipping on the ‘scope and compare with the two bias values. Most users of tube equipment, unless they’re really into the technical side, never check tube bias 1568s. Who knows, you may find that the “correct” bias voltage based on the graph is in between the two values printed!


Instead, contact your nearest service center! There are some nice articles online which show how to interpret deviations in the waveform appearance and form some correlation with distortion. The only thing I can see would happen by altrc the setting to volts would do would decrease the idle current through the EL34s and probably increase tube life, however, would lowering the plate current in this manor change the sound that much as well?

If you have, or can borrow, alhec copy of the Altex Designer’s Handbook it will give you everything you need to graph virtually anything. They were intended for use in churches, bowling alleys, shopping malls, dance halls, high school auditoriums and, naturally, movie theaters.

Just off the shoulder of Orion. Register a new account. In any event, you certainly have a good handle on what’s needed here to answer the bias question. As such, they are designed with certain technical features that would make them immune to most alte the common mistakes a non technical operator might make such as running them with no load.

Sign In Sign Up. In addition, some files are archived, so you need WinZip or WinRar to open that files. The power supply is good, but could use a choke and good caps.

They work excellent and I plan on keeping them all original as they just have too much vintage appeal to change them. Sounds like you want to have some “fun” with this! The difference in bias voltage between the 2 schematics remains a mystery. 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 account in our community.


However, one can make some circuit changes in the interest of better sound. If you are not familiar with electronics, do not attempt to repair! I have lived and breathed tubes for the past 50 years and still marvel at the amazing things that they can do!

PRMAug 2, You could always put a ‘scope on the output with a proper load connected and see what effect the altered bias has Fanatic, I do have a scope I could look at the change with. No, create an account now. Posted September 19, The amps are large enough and easy enough to work on that you can do almost anything you want with respect to refining the circuit for your own use. Is this a good assumption?

Wanted: Peerless power transformer (for Altec A amplifier)

You can try that for multiple frequencies to get some appreciation of what’s happening across the audio band. I’m thinking I should just measure the plate current at either setting and alec what value fits the EL34’s recommended plate current curves the best.

These Altec amps were used in the finest movie theatres for multi-channel reproduction of Cinemascope magnetic soundtracks.