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Thread: Altec Lansing 1569A Tube Amplifier info needed

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    Altec Lansing 1569A Tube Amplifier info needed

    To Anyone in the know... Please tell me about the 1569A Amplifier. It seems to be a surprisingly high powered amplifier @ 80W per mono-block. It surely must run in Class B. Is this the case or does it run in some form of AB? I kinda think it would have to be Class B; just wondering if anyone knows.

    I would love to hear all your thoughts on it. Is there any "fluidity" to be had with this amp, or is it a hard core & hard edged audio signal power provider that was used in cinemas??? ....where & when back in the days these amps were in vogue cinemas weren't known for their "hi fidelity"

    I know about the limited bass response. I am tri-amping and am only interested in using it for midrange or treble reproduction, and would not be using it below 500 Hz or higher. I would even make use of and switch on the amp's 250Hz filter for that extra safety.

    I am looking forward to your comments regarding its use for mid or treble reproduction. They would be driving Smith horns (full sized or minis) with JBL drivers, 2445 or 2447 if mid, 2402 if driving tweeters.

    I'm even thinking of 'trying out' the 70V tap to see if the amp operates as a "constant current source" in that manner on its high impedance output tap. I think I may need to alter the feedback circuit slightly to achieve this however.

    Thanx all,
    Steve

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    I don't mean to answer my own question and still hope to hear from others ... but looking up the tube data for the 6CA7 power tubes, I see it's capable of providing 35W for a pair in push-pull biased for AB operation ; and I know this amp uses 4 of them as power tubes.... so, really pushing it into distortion I can see how regardless of frequency or quality, it could be rated @ 80W. So I guess this amp maybe does run in AB mode. Still hoping to hear from anyone with experience with these amps though.

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    Some information you can find here:
    http://www.one-electron.com/FC_ProAudio.html
    Others will have experience.
    (The 70 V tap is not intended for usage with 4 -16 Ohm speakers, did you know?)
    ___________
    Peter

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    Thanx that annotated schematic; helps a lot.

    I'm interested in trying the 70V tap to drive a single driver (no passive x-over) by a high impedance source. I'm looking to experiment with constant-current /aka/ variable-voltage /aka/ impedance-follower amplification. I'm 'hoping' however using it with a 8ohm tweeter or 16 ohm midrange won't overload the transformer and either saturate it or draw too much current for the windings. ...not sure that just a high impedance tap will make it a constant-current amp. I think a mod to the circuit would be called for.

    Looking @ the circuit, I see a similarity with the way you design an op-amp based constant-current circuit. That is you float the ground of the speaker with a 1 ohm resistor, and you tap a feedback resistor from that (between the (-) of the speaker and the resistor) back to the input to the opamp; creating a variable gain based on output impedance. I notice that if I connect the feedback transformer tap to the COM of the speaker out, perhaps with a sub-1 ohm resistor in series, it is quite similar to the way you make an opamp into a constant current source. ...MAYBE. Worth the try.

    With all that amp's feedback, do you (or anyone) know if it's got a high level of IM?

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    Quote Originally Posted by m8o View Post
    Looking @ the circuit, I see a similarity with the way you design an op-amp based constant-current circuit. That is you float the ground of the speaker with a 1 ohm resistor, and you tap a feedback resistor from that (between the (-) of the speaker and the resistor) back to the input to the opamp;
    You are knowledgable, I see. You should consider that open loop gain of a tube amp is not that high, so the load for the tubes may be too low (smoking transformer).
    Good luck!
    ____________
    Peter

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