Ampeg B-15S response switch wiring please help.

[jatchley]

Hello. I need help figuring out which leads from the switch go to which pads on the pcb. The schematic confuses the hell out of me for this part. It’s a 3POS switch with 2 wafers with 14 leads coming off of it. One of the leads isn’t shown in the switch drawing because I know it is a ground. In the PCB diagram this switch is cited as “SW1”

[g1]

I think you will need the datasheet for the exact switch.

[vintagekiki]

https://www.andybaxterbass.com/products/1976-ampeg-b15s



click to enlarge

[Enzo]

No reason to think the switch is weird. The schematic looks pretty clear to me.

[vintagekiki]

...leads from the switch ...

PDF
B15S schematic (12/71)

PDF
B15S schematic (5/77)

[jatchley]

I don’t think it is weird I just don’t fundamentally understand how to read that switching on the schematic. I have the documents suggested already. But I don’t know if the switch is 3 pole or 4 pole. I don’t know what leads are inputs or outputs on my drawing. I don’t know how to deduce the internal connections in the switch. The switch is no labels or lug numbers. No specific switch info or wiring is really given in those PDFs except “sw1” 13 times. I have a switch with resistors and leads hanging off of it. I’m not sure what connections are happening inside the switch. I’m guess I’m asking for help in matching them up because I’m lost. I saw that picture of the underside of the board already as well and it’s just not detailed enough to be able to really tell. I appreciate the replies tho because I’ve been asking a lot of people and getting no bites.

[jatchley]

Like what are those dotted lines on the schematic? Leads? If so which ones? And one thing that will help confirm for me what’s right is that the leads are snipped straight from the board. So their length kind of tells me a vague area. But on the pcb they are grouped fairly well on that one side. I just don’t want to play guess work ya know? I’ve been looking up rotary switch wiring stuff in general for days and I just still am not digesting it right or something. I know this amp is fairly well spoken of and with the massive amount of vintage Ampeg fans I’m surprised there’s so little documentation about tech experiences with this amp. I got it for a deal and am rebuilding it and in all my pictures the entire chassis was covered in lots of black powdery stuff. So all the leads were black til I cleaned everything. I didn’t have the foresight to realize I couldn’t figure out that part of the schematic before I removed the switch.

[Enzo]

The dotted lines indicate a mechanical connection. You might see a dotted line from the AC power switch to the volume control of some amp. AN am that you turn the volume past zero to turn it off. The dotted lines indicate that all those switch sections are worked by the same knob.

Learn the difference between a pole and a throw. or position. You have a three position switch. Offhand I see SIX poles in the switch, each of them has three positions (three throws)

In each switch section, the pole is the arrow. The arrow can be switch to one of three positions: G, F, or B. SInce they all work together, if one switch is set to B, the other five will also be on B.

Is the switch wafer exposed to be seen? Or is the switch enclosed? In each section of the switch the moving pole, often called a common, can be moved to contact one of three terminals. In an exposed type switch you can see the moving contact mating to the position contacts.

Look at the farthest left switch section. The dotted line points to the common terminal, whose arrow is pointed at the F terminal. That common also connects to pin 3 of the tube as well as the top end of R5. Note the B and F terminals have no connections only the G position connects the common to the bottom end of R5. So in the G position the switch shorts across R5, othewise R5 is in teh circuit.

Looking to the right at the next two sections. Note the two commons are connected together and to nothing else. So the switch there is the path through the stage. In section 2 note the B and F are wired together. In the G position, it adds R7 into the circuit.

You can go section by section across the drawing and analyze. You have the board layout, so you can identify R5 or R7 or whatever ald find the wire points for each to go to the switch.

Note in the photo below, the common is the terminal just slightly right of top center. Note it is longer to contact the common ring near the center. Then the little moving contact fits into each of the position terminals.

[jatchley]

Wow thanks! That helps me read the schematic a bit better. I think the switch is enclosed. There’s a semi transparent disk on top of the poles. I can see an X shaped part move with the position of the switch but it’s not clear enough to determine if it’s shorting or not. My plan now is to go through and measure continuity between all the leads in every position of the switch. And try to determine what leads are for B,F,G or common.

[jatchley]

Well the drawing I did of my switch is wrong and the forum won’t let me change it or upload anymore so idk what’s up with that I’m new to this forum. I did connection testing of the switch and came up with this. Still kind of overwhelmed. But I’m trying to go slow and understand. I feel like I’m close.


No resistance continuity:
A+N (Guitar)
M+N (Guitar)
B+C (Guitar)
I+H (Guitar)
J+D (Guitar)
E+G (Bass)
C+F (Bass)
L+K (Bass)
K+N (Flat)

Resistant:
A+N 5.6M (Flat,Bass)
A+M 5.6M (Guitar)
A+E 1M (Bass)
A+J 6.8M (Flat,Guitar) 1M (Bass)
A+D 12M (Flat) 6.8M (Guitar,Bass)
A+K 5.6M (Flat)
D+E 5.6M (Bass)
D+G 5.6M (Bass,Flat)
D+J 5.6M (Bass,Flat)
D+K 6.8M (Flat)
D+M 12M (Bass,Flat) 1M (Guitar)
D+N 6.8M (Bass,Flat) 1M (Guitar)
E+J 100k (Bass)
G+J 100k (Bass,Flat,Guitar)
J+K 1M (Flat)
J+M 6.8M (Bass,Flat) 1M (Guitar)
J+N 1M (Bass,Flat,Guitar)
K+M 5.6M (Flat)
M+N 5.6M (Bass,Flat)

All the rest of the connections test as not connected.

I do know that lead N goes to the Vref of the volume pot. And lead G goes to ground. I suspect lead A and lead E also as ground.

[jatchley]

Here’s a link to the updated switch drawing

https://el34world.com/Forum/index.ph...ch=92522;image

[vintagekiki]

...Here’s a link...

Advice
When you give some information, give it complete, do not share it with a spoon.
Here is a link

https://el34world.com/Forum/index.php?topic=27666.0
B15S Response switch wiring.

[jatchley]

What do you mean? I’m asking the same question in various places to help my chances of someone somewhere helping me.

[jatchley]

Ok I’m going to try and figure out what wires are for what sections. Let’s start with the bass? So lead E in my switch drawing is supposed to grounding something on the board when in Bass position only. Since G is a known ground and there’s open continuity between E and G in bass position whatever has continuity to E is on it way to ground. This connection to ground from E is lifted in both flat, and guitar settings. Also C+F is open in bass position only is that a bypass or something? Also i see that J in all positions goes to ground as well would that go to the junction of r7 and r8? but then how does the top of r7 work? Would that be something like D? Am I doing this right?

[vintagekiki]

Ampeg B-15S response switch wiring
Check may be minor errors.



vk