GK 250ML speaker wiring

[Helmholtz]

I'm speaking of minimum necessary power/SPL in a band with a rock drummer.
While a 20W guitar amp or a 50W bass rig typically is not sufficient, doubling power often works (at least for reheasals or club gigs).

[g1]

I'm just saying that the general rule is that doubling power gives the same gain in SPL as doubling the speakers.
So if you are not loud enough with a 50W & half-stack, either going to 100W with half-stack, or going to 50W with full-stack should give the same SPL boost. Generally.

[Helmholtz]

I'm just saying that the general rule is that doubling power gives the same gain in SPL as doubling the speakers.
So if you are not loud enough with a 50W & half-stack, either going to 100W with half-stack, or going to 50W with full-stack should give the same SPL boost. Generally.

I understand.

My point of post #12 was that doubling power can make a significant difference - depending on circumstances.

[loudthud]

For those who have never played through one of these, they are way cool. Warm sound like a tube amp because of the JFETs in the signal path (U2, 5, 8, 9), and the chorus just makes it better. Outstanding design for the time.

[J M Fahey]

Thanks to both of you.

Speaking of the 4 pin connector on PCB, and as shown :

* yellow touches R127 so is one speaker (let´s call it "A") MINUS connection, for confirmation it must also go to matching ext. spk. jack, to its "ground" terminal.
Not REAL ground because it floats above R127 but closest to it anyway.

* orange touches R125 and C49 so it´s "speaker A" PLUS connection , it must also go to matching ext. spk. jack, to its "hot" terminal.

* red touches R133 so it´s "speaker B" MINUS connection , it must also go to matching ext. spk. jack "ground" terminal.
Again not REAL ground because it floats above R133 but closest to it anyway.

* brown touches R128 and D28 (If I read them right, PCB solder side is fuzzy) so it´s "speaker B" PLUS connection , it must also go to matching ext. spk. jack, to its "hot" terminal.

Notes:
*I* labelled speakers "A" and "B", check you see them the same way.

Found PCB power carrying tracks (speakers and rails) "thin", but hey, if they work ....

[sweatyk]

Thank you all for your replies. I struggle in reading schematics with things like this. I can usually muddle through them but sometimes I just can't grasp it. The speaker availability I have researched and through other threads read that GK no longer offers replacements....they actually have gotten away from their guitar amps (including parts) and sticking to bass amps. It is difficult to find 16 ohm speakers this size. I have read that 8 ohm speakers can be used but I would need to disable the external speaker connections which I would rather not do. I do plan to sell these amps sometime down the road and want them to function as designed. This amp hasn't had speakers in them for 15 years and I didn't pay attention back then to record where the wires go. I know that is a stupid move. However, over the years I either take pictures or draw diagrams before disassembling things. I bought a donor amp years ago for the speakers. Now I need another pair because I have resurrected the donor amp. I keep checking eBay for parts amps.

I really appreciate the help with the speaker wire orientation.

[sweatyk]

Also wanted to point out being it was mentioned, the +/- tabs on these speakers are marked positive with a red paint dot near one of the tabs.

[Enzo]

Well, if you have any discipline at all, you don't need to disable the external jacks, just don't use them.

[glebert]

Could it be rewired with switchjacks so that if you plug in external speakers it disconnects the internals? Once you hook up an external cab I would think the internal speakers are kind of moot anyway.

[J M Fahey]

^^^^^^^^ That!

Even more , I was chiming in to suggest 2 mods:

1) as suggested by giebert, rewire using switching jacks so internals get disconnected, and you can plug a couple nice 10"/12" speakers , 8 ohm each, so they get FULL power.

2) since you need 2 NEW 6" speakers, also get them in 8 ohm each, much easier to source but more important, they will also get full power.
That tiny amp will become a fire breathing dragon.

Well, a small one at least

Not many good powerful 6" Guitar speakers around, typical is 15/25W RMS as found in small "practice" amps, and typical 6" Woofers are low efficiency and muddy as hell (for Guitar use) so as an alternative I suggest getting a couple of these, impressive high quality PRO midrange speakers made by Faital Pro.
https://www.parts-express.com/Faital...8-Ohm-294-1152
They have Bass to begin with but more important, they reach high because they use light Aluminum wire voice coils, full power from 100Hz (impressive for a 6" speaker) to some 4500 Hz (Guitar band), and very flat.


They are perfect for modellers and in any case G&K creates all the magic in the preamps, power amps are essentially clean and flat.

[g1]

I was under the impression that he already had the 16ohm replacements and was installing them, but I could be mistaken.

[loudthud]

With +/- 45V rails, I would expect power output at clipping to be closer to 100W at 8 Ohms. (80V pk to pk)