Fender 75 Combo...vintage....

[bsco]

Hi there. Somebody dropped off a Fender 75 combo...This amp has a switch for power selection and it also has a lead volume and lead master controls as well as the normal clean channel volume and master volume controls. Is the lead channel switchable by a foot switch....as one did not come in with the amp...or does the lead channel work in conjunction with the normal volume controls?? Also, how does the power level switching work as when I flick this switch it doesn't appear to do anything.....Checked the switch and it is good....Will have to scour the net for a schematic...Is there any quirks that are inherent to this amp?? I had to replace the two output tubes....actually, they were loose around the base on the tubes themselves so I replaced them..the power switching and seperate lead volume and master controls have me a bit confused. Any advice, etc....greatly appreciated.....
Cheers,
Bernie

[pdf64]

Schematic http://www.webphix.com/schematic%20h...r_75_schem.pdf
Footswitch info http://www.stratopastor.org.uk/strat...ootswitch.html

[52 Bill]

Here's the schematic link
Fender 75 | Ampwares

Is the lead channel switchable by a foot switch....as one did not come in with the amp...or does the lead channel work in conjunction with the normal volume controls??

Yes, the lead channel is foot switchable, but it requires a special switch with leds in it. There are one set of tone controls but two sets of volumes. One volume set (Volume and Master) works with the clean channel and the second volume set (Lead and Lead master) work with the lead channel. I don't remember if there is a front panel switch to change the channels or not.

Also, how does the power level switching work as when I flick this switch it doesn't appear to do anything.....Checked the switch and it is good....

The power level switch actually reduces the voltage to the amp by 1/2. So in high power mode, there is 500 volts dc being supplied to the amp circuits, and in low power mode there is 250 volts dc. When you play the amp at low volumes, there will be no apparent difference in the sound of the amp. But when you play at higher volume levels the low power position will have less overall volume and headroom.

[g1]

It will be difficult to hear the power difference unless you really crank it loud, then the low power setting will give less headroom/earlier distortion.
From what I recall, you need the footswitch to get some of the lead controls and there is no other footswitch like it.

Edit: Seems three of us were posting at the same time. Some other Fender's of the same vintage also used that footswitch (p/n 017007 ). Schematic is on the footswitch link pdf64 posted above.

[bsco]

I went in earlier this afternoon and checked the plate voltages as I switched the power selector switch from Hi to Lo...(I had found a schematic)...and the plate voltage changes fine. So now I know that it is switching....I didn't realize that I had to crank it up on almost full....I checked out the info on the footswitch and had a look. It is different indeed.....I don't think the guy has the switch but I'll ask him. As far as that goes, the only thing I have left to do is to replace a scratchy pot. Other than that, everything seems to be working fine...Thanks for all the help and links.....
Cheers,
Bernie