GK 250ML speaker wiring

[sweatyk]

This unit did not have speakers in it so I wasn't 100 percent sure where the wires go. The red and orange wires are connected to the positive side of the speakers. Does this look correct?

[J M Fahey]

Please post the schematic.
That picture without context means next to nothing

Also clearly show terminals on both speakers, and any marks/signs/labels/colour dots/ whatever identifies them.

As shown, the lower one (in your picture, they are actually side by side) is dark/fuzzy, no marks visible, and the upper one is directly hidden.

[g1]

250ML is a stereo unit that uses 8ohm speakers. (edit: incorrect, internal speakers are 16ohm, minimum load is 8ohm per side)
You have to make sure the + an - for each come from the same 'side'.
Schematic on pg.12 of attached.

[sweatyk]

Please post the schematic.
That picture without context means next to nothing

Also clearly show terminals on both speakers, and any marks/signs/labels/colour dots/ whatever identifies them.

As shown, the lower one (in your picture, they are actually side by side) is dark/fuzzy, no marks visible, and the upper one is directly hidden.

Sorry about that. Here is 2 pages from the service manual. The second one is the PCB layout. The speaker connection on there is highlighted in yellow and the wire colors from left to right on the harness are ....yellow, orange, red, brown.

On the speakers themselves the tab orientation if the speaker is face down the positive tab is on the left side and negative on the right.

[sweatyk]

250ML is a stereo unit that uses 8ohm speakers. You have to make sure the + an - for each come from the same 'side'.
Schematic on pg.12 of attached.

g1 these internal speakers are rated at 16 ohms each. Replacements are EXTREMELY hard to find.

[Enzo]

Did you CALL G-K and ASK if the speakers were available? And if so, from where?

Speaker terminals. Many if not most speakers mark the positive terminal. A lot have a small + stamped into the fiberboard. Others have a red spot by the terminal.

Since absolute polarity isn't really very important in a guitar amp, you can just look at the speaker, 6terminals pointing up, and consider the one on the right positive - usually is anyway.

If you want to be oficial about it, test it. Get a 9v battery and touch it to the terminals briefly. It won't hurt it. Turn th battery so the cone moves OUTWARD when the voltage is applied. The termonal with the battery positive on it is the speaker positive.

[52 Bill]

Looking from the front of the amp, at the 4 pin speaker wire connector the pin farthest to the left (let's call it pin 1) and the third pin are negatives and pins 2 and 4 are positives.

I rarely see an original speaker that is blown, lots and lots need refoaming, but it is rare that a voice coil gets cooked.

[Enzo]

As oriented in your layout, the four pins on the yellowed connector are left to right:

Top channel negative
Top channel positive
Bottom channel negative
Bottom channel positive.

Top and bottom are just my terms for the upper and lower portions of the schematic. WHich is which doesn't matter, just don't cross-connect the speakers and channels.

[g1]

16ohm speakers will work fine, you will just get a bit less power out of the amp.

[Helmholtz]

16ohm speakers will work fine, you will just get a bit less power out of the amp.

SS amps are voltage sources. Means that available output voltage doesn't change with load - as long as supply voltages don't significantly sag.
Output power is given as Pout = V²/R, so doubled load gives half power.

[g1]

So half power is 3db down in SPL yes? I should have said 'a bit less volume' rather than a bit less power. My mistake.
In my experience all SS amps have considerable sag at full power, so it never works out to exactly 1/2, probably more like 2/3.

I was also wrong about it using 8 ohm internal speakers. The number shown on the schematic is for minimum load. The ML came with 16 ohm speakers and you can add 16 ohm ext. spkrs. for total 8 ohms per side.

[Helmholtz]

So half power is 3db down in SPL yes?
.

Yes, 3dB in SPL. Sounds little but can make all the difference in a band context.

Agree on 16 Ohm nominal load here.

[g1]

3dB in SPL. Sounds little but can make all the difference in a band context.

Like the difference between 1/2 or full stack.

[Helmholtz]

Like the difference between 1/2 or full stack.

Not sure what you mean.

I'm speaking about the difference between a 50W and 100W bass amp.

[g1]

Not sure what you mean.

I'm speaking about the difference between a 50W and 100W bass amp.

I meant the 3db SPL gain from doubling up on speakers, like the same Marshall head running into full stack rather than 1/2 stack. In each case we should get 3db boost in SPL.