[Harp-L] FENDER BLUES JUNIOR AMP: HOW TO MODIFY IT FOR HARMONICA

["Gianfrancesco Leone" <gianfrancesco_leone@xxxxxxxxx>]

My name is Gianfrancesco, I'am an harmonica player from Rome, Italy. 
I would ask you an advice: I have a Fender Blues Junior Amp. Someone told me that is possible to modify it for the harmonica, making something to the tubes...I don't know exacltly. I think I have to change the tubes (all of them or just someones?). I'd like to have a better, more "saturated" sound and, above all, to reduce at most the feedback/larsen effect. 
I know a very skilful technician in Rome who said me: "Sure I can do it, but I need to watch the changed circuit scheme". I believe him because he is very clever and not at all expensive. But how can I get this special plan? What do you think about? 
Which kind (brand) of tubes are the best for the blues junior? And, besides of tubes, what else could I do further? 

Does anyone have any suggestions?
Maybe someone could send me the grafic of altered circuit scheme....
Any advice would be appreciated.

Thank you and regards,
Gianfrancesco.