Upgrading speaker terminals of Dynaco ST70 - diyAudio
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Old 3rd March 2011, 01:58 AM   #1
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Default Upgrading speaker terminals of Dynaco ST70

I'm thinking of replacing the present screw-type speaker terminal strips of my newly acquired Dynaco ST70 with 5-way binding posts for the use of 8 ohm speakers. Being a relatively newbie, I'm not quite certain about how to connect the wires to the binding post.
The 1st picture shows the back of the speaker terminal strip which has screws connectors for 'C' (I assume this is common or ground), 4-ohm, 8-ohm and 16-ohm. In the pic, wire 1, which is connected to the chasis, and wire 2 (from the output transformer) are connected to the 'C' of the strip, wire 3 to 4-ohm, wire 4 to 8-ohm and wire 5, together with wire 6 (connected to a resistor on the driver board), to 16-ohm.
I've come across 2 types of binding posts as shown in other two pics. One type is different with additional stick-out strip connector. Can anyone tell me the difference between these two types of posts? Which of them should I use to replace the old terminal strip? As to the connection of wires, is it that only wires 1, 2 & 4 need to be soldered to the binding posts for 8-ohm speakers, and the other wires need only to be safely treated by covering their leads with electrical tape? Advice will be highly appreciated.
Attached Images
File Type: jpg P1110505-1.JPG (58.5 KB, 107 views)
File Type: jpg bindingpost.jpg (13.3 KB, 99 views)
File Type: jpg bindingpost2.jpg (33.7 KB, 100 views)
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Old 3rd March 2011, 10:39 PM   #2
wwenze is offline wwenze  Singapore
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According to the schematic here, you need wires 1,2, 4, and 6 needs to be connected to 5.
Dynaco ST70 Tube Amplifier Schematic

I would prefer not to use binding posts with a large part of exposed metal. Too much risk of short-circuit and there is no real purpose of leaving it exposed except to look good.
You can solder the wire directly to the post but the connection won't be physically secure, hence the proper way is to solder it to a ring connector or that additional strip connector and then secure that on the post with a nut.
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Old 4th March 2011, 02:19 AM   #3
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Soldring dirctly to the end of the binding post eliminates a mchanical connection, and likely works better, you need a big iron to get the solder to stick. Electrically the tabs are OK to use in a speaker. In an amp where they may bend and touch something they shouldn't are wouldn't recommend using them.

From the pics i'd pick the 1st set of posts in a heartbeat, much less metal. These will also be the ones that are easir to solder to. They are often seen in intrumntation. The 2nd set have more bling and are dsigned to sell on the basis of "mine is biggr than yours"

In amps, these are what i prefer using.

Click the image to open in full size.

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Old 4th March 2011, 05:50 AM   #4
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Quote:
Originally Posted by wwenze View Post
According to the schematic here, you need wires 1,2, 4, and 6 needs to be connected to 5.
Dynaco ST70 Tube Amplifier Schematic

I would prefer not to use binding posts with a large part of exposed metal. Too much risk of short-circuit and there is no real purpose of leaving it exposed except to look good.
You can solder the wire directly to the post but the connection won't be physically secure, hence the proper way is to solder it to a ring connector or that additional strip connector and then secure that on the post with a nut.
I'm not good at schematics. So, would you tell me why wires 5 & 6(presently wired for 16-ohm) are still needed when I'm only going to use 8-ohm speakers and if they are really needed, to which of the binding posts should they be connected? Am I right in the thinking that wires 1 & 2 are to be soldered to the tip of the black binding post and wire 4 to the tip of the red binding post?
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Old 4th March 2011, 11:10 PM   #5
Enzo is offline Enzo  United States
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Wire 6 is your negative feedback to the amp circuits, and it is connected to that 16 ohm tap (wire 5). You don;t need to connect 5 and 6 to binding posts, but they need to be connected together.

Yes, 1,2 would be the black post and 4 the red.
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Old 5th March 2011, 07:45 PM   #6
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Originally Posted by Enzo View Post
Wire 6 is your negative feedback to the amp circuits, and it is connected to that 16 ohm tap (wire 5). You don;t need to connect 5 and 6 to binding posts, but they need to be connected together.

Yes, 1,2 would be the black post and 4 the red.
Thanks. So, after connecting wires 1&2 to the black post and wire 4 to the red, I can appropriately tape exposed leads of wire 3 and wires 5/6 to prevent touching the chasis and let them hang loose, right?
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