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puppyslugg 18th November 2002 10:25 PM

Altec 1570B amps
Vacuum Tube Valley did a article regarding the Altec 1570B. Does anyone have any info or copy of the article?


fdegrove 19th November 2002 11:44 AM


This is the circuit diagram:



puppyslugg 19th November 2002 06:15 PM

Thanks, fdegrove.

I wonder if anyone have info on the mods Vacuum Tube Valley did?

dshortt9 22nd November 2002 05:49 AM

I had a pair of these and modified them quite a bit. I changed the rectifiers to solid state, used 812's 572-30's, 572-10's, changed the input tube to a 5687, changed the output tranny to $440 custom made ones, changed the 6sn7 values, replaced the 6w6 with 5881's and finally realized that the weak point wth these amps is the mystical swinging choke used with the 6w6's to drive the outputs. SO after much ado here is the best thing to do. Make sure that you bypass the 70 Hz filter in the input circuit and connect the input directly to the 12AX7 grid. Use 812's with an appropriate change in the cathode bias resistor, I'll come up with a value if you are interested. That's all you can do to improve the sound to a certain point. Great mids and highs but mushy Bass. Then experiment with a way to eliminate the swinging choke drive, probably by substituting a Mosfet in the circuit and eliminating the 6W6, 6SN7, and 12AX7 stages. More if interested.

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