Ampeg B-15S response switch wiring please help.

[jatchley]

Oh I see those are the poles! Got it. Now if I can figure out the web of connections on the switch I’ll be good. Thanks.

[jatchley]

I’ve deduced that lead J should go the the junction of R7 and R8? Since it’s a 100k to ground. And then lead M since it’s the only 5.6M that is on the guitar setting only goes to the junction of c5 and c8? That would mean lead A goes to a ground point? That makes sense to me because it is black like the other ground lead. Does that seem right? It’s taking a while but I’m working on it. Just need some confirmation. I’m trying to just work off of the grounds first? This still feels like guess work. And is still very confusing without knowing how the leads are grouped on the switch. We’ve established the switch has at least 6 poles ok. And in the previous posts it was established what poles go to what. So how do i determine how the leads hanging off the switch are grouped? I’m realizing some of my measurements might be redundant if I was measuring an input to input.

[Enzo]

I know you are trying hard here, but honestly the switch drawing leaves me baffled. I want to see a switch in its parts, and then I can determine where the circuit needs to connect. With just a round circle with terminals, I have no idea what is what inside. I cannot advise in that case.

[jatchley]

Here are some pictures of the switch from all different angles. The first 3 being from the back in different positions.

the pin out is the same as the drawing in the folder. The wafer on top with lead A is the closest to the faceplate. The bottom is the back the one you see inside when looking in the chassis.

I put the schematic, pcb diagram, switch drawing, and a bunch of pictures of the switch from different angles.

https://drive.google.com/drive/folde...RBYE43iGTTHTOX

[jatchley]

I want to add that vintage blue just replied to my email and said “ it appears to be eight 3-pole switches (only six are used) stacked on a common shaft. It looks like each ‘switch’ consists of a group of 4 contacts – 1 common contact that gets connected to one of the other 3 contacts in the group, depending on the position of the switch.”

[The Dude]

No need to guess or assume. The ohmmeter is your friend.

[vintagekiki]

Open HEIC files with Ultra File Opener

https://www.ultrafileopener.com/formats/heic/

From the attached pictures I don't see that the problem is in the switch.
As far as can be seen all the wires are neatly soldered.
Switch 1 has 2 wires
Switch 2 has 3 wires
Switch 3 has 4 wires
Switch 4 has 3 wires
Switch 5 has 2 wires
Switch 6 has 4 wires
What specifically is missing in the sound.
Do all 3 presets work (guitar / flat / bass)
Try to track whether each wire from switch SW1 goes to its place on the PCB

[jatchley]

The entire switch is disconnected from the main pcb. I’m trying to re-connect it. The amp was pitch black from something exploding and catching fire with the previous owner. The previous owner sold it to me as is for a good price and the Transformers test good, most components test good. Switch is still in factory wiring. It was stock when I got it. I disassembled the amp after taking pictures so I could clean everything. I did this thinking I was going to hand wire a B15N inside. Suddenly all these black wires became color wire. And the pcb looked wayyy better. After reaching out to old SLM techs they said the pcb was savable and to bring it back to stock if I wanted it to hold value. So I started restoring it as stock as possible and then I got lost tracing the schematic to re connect the switch after it was cleaned. I looked at my pictures and found all the wires were black. My mistake here was disconnecting it in the first place. And not knowing how rotary switches work. I personally don’t know how to deduce the way it works. The switch does work though. It’s just about matching the leads labeled A-N in my switch drawing to the specific pads that are numbered on the pcb diagram in that google folder. My continuity test is also in that folder.

[Enzo]

Fair enough, I can't really see the innards. But the ohm meter advice is good, determine which contact is common and the three positions associated, then you can group the wires to the board.

[vintagekiki]

I got lost tracing the schematic.

For service manual see

#5

https://www.vintage-blue.com/assets/b15s_1971.pdf
B15S schematic (12/71)

https://www.vintage-blue.com/assets/b15s_1977.pdf
B15S schematic (5/77)

[vintagekiki]

I disassembled the amp

You will perform the repair step by step.
Carefully inspect the PCB and replace any suspicious parts.
Check the power supply and check that all voltages are present.
Check the complete power amp and bring it into operational condition.
When the power amp (V3 to V6) is serviced, connect the spkr cab to J6 (Ext Spkr) and put the guitar into J5 (Ext Amp) to check how the power amp works.

Check preamp (V1) and bring it to operational condition, without response switch, by connecting C2 (0.1) directly to the hot end of VR1 (1M lin)
When the complete Ampeg B-15S is operational, arm yourself with patience for response switch wiring.

Tip.
Do not desolder anything with the response switch.
Since SW1 disconnected from the main pcb with the ohmmeter test all its functions and the associated hardware.

[catalin gramada]

Those AC loading path looks wrong to me. Think There is 100nF coupling cap into 100k resistor parallel with 1M pot. This will determine around 15 cps pole and cca. 10x voltage gain. You can switch to 10nF and 1M pot for the same 15cps cutoff point but ac voltage gain will be almost x40. There is too much and will do the volume pot to be useful for a fraction keeping a large resistance into the next grid with all consequences of HF rolloff due to miller capacitance.

[vintagekiki]

path looks wrong

I'm afraid you've confused some cups.
See B-15S schematic how is connect volume control at channel two (tube V2)

[catalin gramada]

I'm afraid you've confused some cups.
See B-15S schematic how is connect volume control at channel two (tube V2)

Missed that. Yes, the second ch. seems extremely particular voiced, especially for a bass instrument.I wonder how much the OP found it usable. By comparison the V4B who is the big brother of B15S used the same first stage gain structure I mentioned above in both ch. but seems an apple to orange comparison of course.

[jatchley]

I’ve tested the transformers and they are good. The OT DCR matches the schematic no shorts between windings. The power transformer is near 300-0-300 on the secondaries. And the 6.3 is more like 6.9 unloaded. No issue there. I’ve replaced all the electrolytics on the pcb. I’m waiting for the replacement power filter capacitors and tubes in the mail. I also replaced the .047 film cap in the bias supply because I heard they take a beating. I replaced all plate resistors with metal film and the power tube screen resistors with fresh 3w. Continuity of the pcb is good. I touched up a lot of bad solder joints. Ive put a 3 prong cord on it. I’ve replaced both fuses with spec appropriate parts. I’m bypassing the polarity switch since the 3 prong cord makes it redundant. I’m thinking about bypassing the aux 2 prong outlet on the back. I replaced any resistor more than 5% out of spec. My only trouble here is the response switch so might as well tackle it while I’m waiting for parts in the mail. The rest of the rebuild is pretty straight forward to me. After I build the power section my first plan is to test all the film caps in the amp for dc leakage and then compare in real life voltages on the tubes to the voltage chart in the schematic pdf. Now that I know how the switch is divided I’ll be grouping the leads according to the 1pin - 3 pin spacing (groups of 4) and going over my continuity test and switch drawing to figure out what’s (B,F, or G) I’m still trying to figure how to tell a common apart from the others. But if I get them grouped and check between the 4 maybe that will be more apparent.