08-20-2015, 01:39 PM
If you wired it just like before, your "as received" wiring could have been wrong.
Testing the speaker isn't that hard. 10 minutes. I believe you said there are 3 wires soldered to the speaker. Unsolder and remove them from the speaker.
It should only take three tries to find the the field coil if the speaker is good.
-- Connect your ohm meter to any two of the terminals on the speaker. Wiggle the clips to get good contact. 1700 ohms? You've found the field coil terminals. Open circuit? Move to next step.
-- Move ONE of the meter leads to the remaining terminal. 1700 ohms? You've found the field coil terminals. Open circuit? Move to next step.
-- Move the OTHER meter lead to the remaining terminal. Same drill as before. This time if you get an open circuit, you really do have a dead speaker. You've tried all three possibilities. Two combinations should be open and the other should be the field coil at 1700 ohms. If the field coil is fried, you still might get some resistance across the field coil terminals.
-- Mark FC terminals with tape or marker so you won't forget. Bad things happen when people connect this speaker up wrong and put hundreds of volts through the voice coil and onto the chassis.
-- Connect the ohm meter leads between the remaining terminal and the metal frame of the speaker, where the fasteners go that hold it to the chassis. Around 2 to 6 ohms? You've found the voice coil terminal. Open circuit? Bad speaker.
-- Mark the voice coil terminal with tape or marker.
If your speaker is good, you can reconnect it as follows. If not, check again & make sure your meter connections are solid.
-- Find the wire that connects to pin 7 of the 7Y4 AND to the positive terminal of the 12 uF filter cap. If connected to a terminal strip, trace it back until you find these two connections. Connect this wire to either one of the field coil terminals that you marked. Can't find the wires or they are connected to something else? Stop and tell the Phorum all about it.
-- Find the wire that connects to the positive of the other filter cap AND to the black wire from the output transformer. Trace it back until you find these two connections. Connect this wire to the other field coil terminal you marked.
-- The remaining wire should connect only to the output transformer, but it might be soldered to a terminal strip before it gets there. Connect this wire to the voice coil terminal that you marked. [edited to add: if you connect your ohm meter between the end of this wire and the metal of the chassis before you connect it to the speaker, you can see if the secondary of the transformer is good. I'm not sure exactly what the reading should be, but a few ohms is typical. Open circuit? Bad or improperly connected transformer.]
-- Solder the connections.
-- Attach your speaker back onto the chassis. (If you want to test it first, connect the metal frame of the speaker to the metal of the chassis with a test lead. This speaker will not work unless the metal frame of the speaker is grounded to the chassis.)
-- Connect your meter leads to the voice coil terminal you just soldered and the metal of the chassis. 2 to 6 ohms? Your speaker is connected properly. Open circuit? Check ground connection 1st, then all connections as above.
Now you know that your speaker is good electrically and that it is connected to the right wires. If it still doesn't work at all, the fault probably is elsewhere.
Testing the speaker isn't that hard. 10 minutes. I believe you said there are 3 wires soldered to the speaker. Unsolder and remove them from the speaker.
It should only take three tries to find the the field coil if the speaker is good.
-- Connect your ohm meter to any two of the terminals on the speaker. Wiggle the clips to get good contact. 1700 ohms? You've found the field coil terminals. Open circuit? Move to next step.
-- Move ONE of the meter leads to the remaining terminal. 1700 ohms? You've found the field coil terminals. Open circuit? Move to next step.
-- Move the OTHER meter lead to the remaining terminal. Same drill as before. This time if you get an open circuit, you really do have a dead speaker. You've tried all three possibilities. Two combinations should be open and the other should be the field coil at 1700 ohms. If the field coil is fried, you still might get some resistance across the field coil terminals.
-- Mark FC terminals with tape or marker so you won't forget. Bad things happen when people connect this speaker up wrong and put hundreds of volts through the voice coil and onto the chassis.
-- Connect the ohm meter leads between the remaining terminal and the metal frame of the speaker, where the fasteners go that hold it to the chassis. Around 2 to 6 ohms? You've found the voice coil terminal. Open circuit? Bad speaker.
-- Mark the voice coil terminal with tape or marker.
If your speaker is good, you can reconnect it as follows. If not, check again & make sure your meter connections are solid.
-- Find the wire that connects to pin 7 of the 7Y4 AND to the positive terminal of the 12 uF filter cap. If connected to a terminal strip, trace it back until you find these two connections. Connect this wire to either one of the field coil terminals that you marked. Can't find the wires or they are connected to something else? Stop and tell the Phorum all about it.
-- Find the wire that connects to the positive of the other filter cap AND to the black wire from the output transformer. Trace it back until you find these two connections. Connect this wire to the other field coil terminal you marked.
-- The remaining wire should connect only to the output transformer, but it might be soldered to a terminal strip before it gets there. Connect this wire to the voice coil terminal that you marked. [edited to add: if you connect your ohm meter between the end of this wire and the metal of the chassis before you connect it to the speaker, you can see if the secondary of the transformer is good. I'm not sure exactly what the reading should be, but a few ohms is typical. Open circuit? Bad or improperly connected transformer.]
-- Solder the connections.
-- Attach your speaker back onto the chassis. (If you want to test it first, connect the metal frame of the speaker to the metal of the chassis with a test lead. This speaker will not work unless the metal frame of the speaker is grounded to the chassis.)
-- Connect your meter leads to the voice coil terminal you just soldered and the metal of the chassis. 2 to 6 ohms? Your speaker is connected properly. Open circuit? Check ground connection 1st, then all connections as above.
Now you know that your speaker is good electrically and that it is connected to the right wires. If it still doesn't work at all, the fault probably is elsewhere.
John Honeycutt
