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modded Slash 2203 chassis innards on Youtube

PostPosted: Sat Feb 20, 2010 3:57 am
by dai h.
anyone check out the chassis in this?

http://www.youtube.com/watch?v=CTFGuP9J ... re=related

According to the video the amp (JCM800 2203) has a sticker on it stating it was modded by Frank Levi (who apparently worked at S.I.R.). Couple things I can see. A cap across 1st stage plate R, a film cap bypass on the 10k cathode R, 0.47uF on the 820/1k position, and a non-stock looking (not a type/brand I can recognize) presence cap (I'd guess maybe a .68uF for more gain). Doesn't look much different from stock, which seems to fit the description of "#34" given on another site.

Re: modded Slash 2203 chassis innards on Youtube

PostPosted: Sat Feb 20, 2010 10:48 am
by Brian Wallace
The cap on the plate would be for high end squeal from the added gain.

I would have to think that if they added a cap across V2, the resistor would be changed as well.

The pres cap has been changed and could be a .68uf generic mylar style cap.

The color code on the V2 cap is hard to read, are you sure it's a .47uf? I kinda see 4.7uf.

Re: modded Slash 2203 chassis innards on Youtube

PostPosted: Sat Feb 20, 2010 2:09 pm
by dai h.
Brian Wallace wrote:The cap on the plate would be for high end squeal from the added gain.


Right, looks pretty normal practice compared to other high gain type schemos I've looked at.

I would have to think that if they added a cap across V2, the resistor would be changed as well.


It might be a 0.1uF judging from the size and looking at other supposedly similar schematics, but hard to say for sure.

The pres cap has been changed and could be a .68uf generic mylar style cap.


It's a blue radial in a style I've yet to see as stock. Seemed to be sort of fat (meaning the size seemed to point to a relatively higher value than 0.1uF).

The color code on the V2 cap is hard to read, are you sure it's a .47uf? I kinda see 4.7uf.


I'd have to look at it again to be sure, but it appeared to be 474 (yel-purple-yel) = 0.47uF.

(edit: looked at it again (used DownloadHelper Firefox extension to obtain the youtube clip and vlc player to watch), and it does appear to be yel-pur-yel-blk-brn)

Overall, the idea seemed to be to goose the response just a bit and not do something very drastic. Looks easy enough for anyone who wants to try, esp. for someone already owning a 2203/4.

edit: (too fuzzy to say for sure, but) there might be a tack soldered R by itself or tacked on parallel on the 10k in the PI. Not sure what lowering the value here would do, say if the modder was going for 6.8k or whatever (just mentioning 6.8k since it's in some Fender schematics if memory serves). Affects PI output drive and asymmetry (less, less)?)

Re: modded Slash 2203 chassis innards on Youtube

PostPosted: Sat Feb 20, 2010 3:35 pm
by Brian Wallace
OK, it's .47uf. I'm on a lap top right now and it's not the best screen for viewing the video.

I would have to think that if they added a cap across V2, the resistor would be changed as well.
Correction, if they added a cap across the 10K resistor, they may have dropped it's value to get a bit more gain.

The tail resistor on the PI does look different from all the rest. It has either been changed or it's what you mentioned.