Bought a 5150 II with an unknown mod

[Room36]

(Sorry if my english is not very good)
I recently purchased a 5150 II and yesterday someone made me notice that there's 3 switches on the back of my amp that are not there on stock 5150's. It's 3 toggle switch, one is a 2 way and the other two are 3 way. I have pretty much no experience with amp modding and I would really like to know what are the functions of these switches, I don't want to blow a tube or damage the amp while playing with these switches. I took some photos (sorry for the crappy quality) and I was hoping someone here could help me figure out what the mod is.

https://www.dropbox.com/s/5iyui9wvwrm14n9/image (1).jpeg
https://www.dropbox.com/s/6l2fvm2utj0ditx/image.jpeg

Thanks !

 

[Heabow]

You cannot ask the guy you bought the amp from?

 

[Room36]

He does not know. He bought it used too and he never bothered about the switches. He lost contact with the guy he bought it from...

 

[NecroDM]

You cannot ask the guy you bought the amp from?

This, also you bought an amp without looking at it first? Did you at least try it before buying it?

 

[Room36]

I looked at it before buying but I never had a 5150 before. I could not know the switches where not supposed to be there. And yes I tried it before buying... And for 400$ I knew I could not go wrong.

 

[newamerikangospel]

Is there not a signature, or sticker on the chassis somewhere? Easiest answer, don't touch them. When you get a chance, take it to a tech. It may be something like tone stack, but it may be a power tube mod as well. I can't really see much from the photos.

 

[nezvers]

And how they change sound?

 

[Loren Littlejohn]

Kind of odd there isn't a sticker or something usually people that mod (unless it's a home brew) have a way of marking their work.

JerryP (FJA mods) uses a gold sticker. He put it on the back of my 5150.

Trace has a small black sticker (voodoo amps).

Have you pulled the chassis out to see if there isn't something on top indicating who did it?

 

[Arsonstudios]

looks like some capacitors in the preamp stage. i heard about some mods using caps to change the sound and get rid of some fizz. but i never heard a modded 5150 so i cant really comment on the sound.
i would be too curious to not just try it if it was mine

this is what i found on the webs maybe it helps:

http://www.rig-talk.com/forum/viewtopic.php?f=3&t=80183

you should check where the leads go to identify the mods. the values of the caps should be printed on the side.

 

[TheWinterSnow]

From what I can see it looks like that is just a mod that changes the capacitance of the cathode bypass cap, could go either way, they modded it to have less capacitance and tighten up the low end (with the other position to a default stock settings) or added more capacitance to add more low end. It looks like it was setup so that the switches allow you to go back to a stock setting and it looks like the switches are setup for each stage (or every other stage) of the circuit.

 

[Fbarre]

Isn't it dangerous in some way to have the wires running so close to those tubes?

 

[loktide]

this is quite far fetched, but judging by the size of the electrolytic caps as well as the location, my guess it that these are for switching in a bigger value cathode bypass caps. This would most likely make the lead channel excessively muddy, mushy and overgained, but could be cool in the clean channel by adding some warmth and saturation.