‘78 JMP 2203 Impedance Selector

[rekelso]

Those spliced wires look to be the OT secondaries to me.
Does look to have been run hard and hot!

I know it needs fresh tubes etc, even I can tell that! So is the impedance selector going to act normally as it’s currently wired? Ie 8ohm is where it should be as if it were stock, 16 ohm and 4ohm the same?

 

[Seanxk]

Take it to a tech and ask him to measure the OT to find out what is what and while he's there get the OT wires under the board where they should be, oh and more importantly that OT isn't original.

 

[neikeel]

The OT installation is reversed (secondaries normally exit through the rearmost chassis holes and primaries front) I suspect if installed in conventional fashion the secondaries will reach directly to the selector although the primaries will need splicing to have best lead dress to the output sockets and HT tie point.
Was it sold as having replaced OT?

 

[rekelso]

The OT installation is reversed (secondaries normally exit through the rearmost chassis holes and primaries front) I suspect if installed in conventional fashion the secondaries will reach directly to the selector although the primaries will need splicing to have best lead dress to the output sockets and HT tie point.
Was it sold as having replaced OT?

No, wasn’t sold as original either. PO said he had it for about 20 years and only had the mains output fixed and it set up for 16 ohm cab which it ran through no bother upon testing. Didn’t know much about previous owner or work done

 

[neikeel]

It is possibly the original turned 180.
You will see people doing that to both OT and PT hoping to change unwanted noises.

 

[rekelso]

It is possibly the original turned 180.
You will see people doing that to both OT and PT hoping to change unwanted noises.

Interesting, I’m really new to amps and a lot of this is still new to me and definitely haven’t heard a lot about these but finding out a lot just from wanting to know whether the impedance selector is set up as original…

 

[Trouble Free]

put a speaker cable in amp (without power) and put an ohm meter on the tip and sleeve of the cable........
Try all 3 positions and write it down.....the highest reading is 16 ohm the lowest is 4 ohm.