Series 300 mod

[Os]

I've posted this question before but I have additional information now. I have a 1982 Series 300, no Reverb so the Presence knob is on the front. On the back, where there should be simply a plug in the chassis, someone has installed a quarter inch jack. We thought at first that it might be a footswitch move but I've had a look inside now. From a point on the corner of the large circuit board, more or less behind the Treble pot, a wire leads to the positive lug on this jack. There's a 3 mf cap bridging the positive and negative lugs and that's it. Does anyone recognize this mod?

 

[Boogiebabies]

It sounds like a gain mod similar to the MK IV's Mid Gain.
A picture would help.

 

[Os]

Thank you. Our digital camera isn't up to the challenge but I think I understand. Plugging a footswitch into this jack and activating it might well produce the same sort of effect as engaging the mid gain switch on a Mark 4. I've been nervous to experiment with it for fear of damaging my amp but I think that I'll try it out. By the way, if anyone out there has an operating manual or schematics for a Mark IIB Series 300 Coliseum head, I'd happily pay for a copy of it. I never knew what loud was until I got this beauty!

 

[Boogiebabies]

If it's a simple cathode cap it wont do any damage. It's only a 2 volt circuit.

 

[Nick_cor]

hey booiesbabies you're still here! i heard you were going to start your own website and sell a couple mark IIC+s or is this just gossip! can you please IM me! glad to see you!