1978 Mark I Rear Panel Questons

[BlackBart]

I recently acquired this 1978 Mark I and it sounds great. I have a couple questions about the rear panel -


1. There's a switch on the right hand side conneting the a resistor network. Does anyone know exactly what it's accomplishing?

2. What is the jack above the Slave jack used for?

Thanks in advance!

 

[Zlofengir]

If I'm not mistaken, the jack above the Slave is the Preamp Return; which can be used in conjunction with the Junction jack on the bottom of the chassis with a volume pedal as an overall Master Volume for the amp. This feature is only on the Mark I and early Mark II's; the link below will explain it all...

Happy tone hunting!

http://thegenerationofmusic.wordpress.com/2012/03/17/guitar-how-to-the-mesa-boogie-mark-iiaiib-ultimate-master-volume-pedal-trick/

 

[BlackBart]

I had the amp serviced and asked the tech about the resistors - they change the bias to cathode.

 

[stokes]

I had the amp serviced and asked the tech about the resistors - they change the bias to cathode.

That switch looks like it just puts the cathode resistors in the circuit.What shuts the neg bias voltage?I put a switchable cathode/fixed circuit in my IIC+ and needed a switch that had to perform 3 seperate functions,the one is your amp only does one.

 

[BlackBart]

I had the amp serviced and asked the tech about the resistors - they change the bias to cathode.

That switch looks like it just puts the cathode resistors in the circuit.What shuts the neg bias voltage?I put a switchable cathode/fixed circuit in my IIC+ and needed a switch that had to perform 3 seperate functions,the one is your amp only does one.

Does anybody know if this is this a factory install or a mod?

 

[hitparader]

My Mark I was a later one, but that switch was not there, I'd suggest it is a mod.