Output Transformer - 4 wires ?

[HaroldBrooks]

National amp output transformer has normal Brown, Red, & Blue wires on the power tube side, but on the speaker side there's another green wire running from the speaker output back up the amp. I didn't want to pull things apart (Yet) to investigate where that wire goes, and I thought someone here might know straight away.

There's no indication on the schematic of any type of negative feedback, but that was my first guess.

Anyone know what that green wire is ?

Thanks for your help !



Here's a pick from a similar amp with the output wire same arrangement.

[Jazz P Bass]

It's only a guess but I would venture that the Green wire is ground.

[HaroldBrooks]

It's only a guess but I would venture that the Green wire is ground.

You guessed well, that's what it was, a ground from the speaker frame to the chassis. I've never seen that arrangement before on a Valco amp, but in my foggiest of memories from when I was a wee lad, I remember seeing speakers that had a terminal connected to the speaker frame, and then grounded.

I've seen so many speakers without that type of ground that I forgot of the concept completely.

Thanks for your help !