I have a pair of these and need directions to bypass/eliminate the 70hz filter on the 12ax7 front end input. From what I've gathered, extensive mods are not needed in order to render these amps hifi. I have basic skills and have done good work with good direction. If there's someone here familiar with this amp it would be greatly appreciated. 🙂 They are in great shape to begin with.
It may be cumbersome for the putput transformer if it han't been designed to sustain lower frequencies without saturating. The trafo and the tube may arcing if this occurs on large signals of lowrr bass tones.
Look for mods by Tom Tutay. I have his schematic somewhere on my computer but I cannot locate it (too much stuff).
The main changes he makes is increasing power supply filter caps, adding stopper resistor to the grid of the 12ax7. Some instability can happen when the volume control is fully up and having a stopper will help.
The output transformer on the 1570 will not do full power bandwidth below 60HZ. The 1570 is better used in a biamp situation on the top side.
I built what is basically the 1570 about 1991 or so and tried assorted driver changes. Really, just more power supply capacitance and screen stoppers is about what I would do.
I have repaired quite a few of the 1570b for someone who still uses them at a drive in. They are still solid performers in that environment.
The main changes he makes is increasing power supply filter caps, adding stopper resistor to the grid of the 12ax7. Some instability can happen when the volume control is fully up and having a stopper will help.
The output transformer on the 1570 will not do full power bandwidth below 60HZ. The 1570 is better used in a biamp situation on the top side.
I built what is basically the 1570 about 1991 or so and tried assorted driver changes. Really, just more power supply capacitance and screen stoppers is about what I would do.
I have repaired quite a few of the 1570b for someone who still uses them at a drive in. They are still solid performers in that environment.
I think you can still expect the 1570 to do 80 watts at 30 hz. Just do not push it too hard.
Really, using them above 60 hz is best though.
What sort of speakers do you plan to use them with?
Probably the best bass slam was when I has a pair of dual 15 in large sealed enclosures followed by the 811 amp from 65 hz and up driving a decent 8 inch driver.
Really, using them above 60 hz is best though.
What sort of speakers do you plan to use them with?
Probably the best bass slam was when I has a pair of dual 15 in large sealed enclosures followed by the 811 amp from 65 hz and up driving a decent 8 inch driver.
I have a vacuum tube valley article that has the Tutay mod and more info on the 1570.
See if this link works or send me an email in a PM.
https://www.google.com/url?sa=t&rct...TV/VTV07.pdf&usg=AOvVaw22z6xF5X3xGPJCJipGlDYy
See if this link works or send me an email in a PM.
https://www.google.com/url?sa=t&rct...TV/VTV07.pdf&usg=AOvVaw22z6xF5X3xGPJCJipGlDYy
Thanks. I want to use them with a pair of Acoustat Model 3. I have a pair of Linn 5150 subs to augment them but I would like to hear them without also.
..and then compare with a pair of folded Acoustat Monitor 3. So 2 sets of servo otl amps and 6 panels per side in a pseudo isobaric configuration.
..and then compare with a pair of folded Acoustat Monitor 3. So 2 sets of servo otl amps and 6 panels per side in a pseudo isobaric configuration.
Last edited:
You just have to look for the two caps between the pot terminal and the 200K volume pot.
You need to inspect them because you never know how they were set with any amp you get. You are basically shorting both caps though you should really use something like a .5 coupling cap. This amplifier with the caps bypassed assumes transformer coupling.
You need to inspect them because you never know how they were set with any amp you get. You are basically shorting both caps though you should really use something like a .5 coupling cap. This amplifier with the caps bypassed assumes transformer coupling.