Fender 75 1x12 combo - I have the schematics: Wiring layout wanted.

[lalunatech]

HiHi

I run an amp repair shop in the UK. I have a 1980's Fender 75 1x12 tube amp in for repair. I have managed to find a schematic for the amp but cannot find a wiring layout diagram for it. The one I have has been modified and I'd like to get it back as close to the original as I can. A good hi-res internal photo of an unmodified Fender 75 would do. Can you help?


Cheers

--
LaLuna Technology | Musicians and DJs Audio Repairs for Hadfield, Glossop, Manchester and Sheffield

[g1]

Have never found a layout, but this may help:
http://music-electronics-forum.com/t27866/

[Jazz P Bass]

I do not believe that Fender has the Layout included in the schematic.

So unless someone can provide a chassis shot, you are on your own.

fender_75.zip

[g1]

In that other thread I linked, Cygnus X1 mentioned he has some pics of the original guts before he modded it. If you send him a PM he may still have them. If he doesn't respond, I think he is still active on some of the other forums. Try googling his user name.

[pdf64]

Also Andy Fuchs mods these, so it may be worth contacting him for any info; if you're lucky may have a stock one handy.

[lalunatech]

Thanks everybody for the helpful info. I will try all your suggestions. A previous owner of this Fender 75 had disconnected the Hi/Lo power output switch, now I know why: The mains power transformer has been replaced with one out of a Bassman/Concert which does not have the isolated bias voltage winding like the original. Also it has a lower HT voltage winding so the amp will only do a fixed 50 Watts now. I have done the best I can with it because the owner did not want to shell out for a new PT.

[lalunatech]

Also Andy Fuchs mods these, so it may be worth contacting him for any info; if you're lucky may have a stock one handy.

Is Andy Fuchs FUCHSAUDIO on here?

[pdf64]

I don't think so.
He's on TGP fairly often Tone Control Choices and Help | The Gear Page and there's his website Guitar Amps, Boutique Amps, Tube Amps, Pedals, Bass | Fuchs Audio

A lower HT is probably a good thing, eg longer tube life!
Without fresh Sylvania STR387, my guess is that you'd be lucky to get 60 watts even with the original PT.
Maybe wire the redundant switch for triode / UL, or to open the NFB loop?

[lalunatech]

Nice ideas for using the High/Low switch pdf64, thanks. I will offer that as an added extra, I have spent way to long on this job already and I am trying to train myself to think more like a Ferengi (ie. is there any profit in this!)

[pdf64]

Just to note that in case your customer ever wants to get his amp back to stock, Hammond make a 75 spec replacement PT now, see https://www.hammfg.com/files/parts/pdf/290YEX.pdf
I think Phil at Bluebell could get one, given a suitable lead time.
Hopefully it may be a bit cheaper than the one from TAD http://www.tubeampdoctor.com/en/shop...erb_70_75W_102

[lalunatech]

I have seen them on sale at mouser.co.uk
He took the amp this morning and paid me, I don't think he'll bother with a new PT.