Marshall SL 5 mods to Silver Jubilee 25/50

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Marshall SL 5 mods to Silver Jubilee 25/50

Postby teknoman2 » 28 Feb 2014, 12:37

Recently I bought the Sl-5 which is a very nice sound amp,
despite that for a couple of days I am trying to modify the sl5 to the jubilee 25/50 specs.
I found those schematics:
Jubilee 25/50
download/file.php?id=21961&mode=view
SL5
viewtopic.php?f=2&t=23280

Do you think If I put the 0.047u on the input (before the 68k), change the 220pf to 47pf on V1 and add parallel a 0.68uf to the 2.7k will make any difference?
Can you please tell me what changes are the best to make the SL5 soundlike a jubilee (if thats possible).

Thanx in advance
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Re: Marshall SL 5 mods to Silver Jubilee 25/50

Postby teemuk » 28 Feb 2014, 14:04

A low power single-ended with entirely different kind of preamp will never sound like a Jubilee. You would practically have to clone the Jubilee preamp and it still wouldn't sound like the real deal because of the entirely different type of power amp.

Those mods you mention are really not going to do anything spectacular. 47nF on the input will at best add just a little bit of low frequency attenuation, the 470pF at the plate circuit a little bit of high frequency attenuation.

If you compare with the Jubilee the Jub has entirely different kind of design in its second and third gain stages plus aided diode clipping. The tonestack is differently voiced too and behaves somewhat differently. The power amp in Jubilee is a high power, class-AB push-pull amp with long tailed pair input section while in SL5 the power amp is a low power, class-A single-ended amp with a common cathode input stage. Both employ negative feedback but entirely different amounts. These power amp circuits will overdrive in an an entirely different manner and sound nothing alike when doing it.

If you want a Jubillee then buy a Jubilee. SL5 won't transform into one without complete rebuilding. You can buy a real Jubilee with much less effort and expense.
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Re: Marshall SL 5 mods to Silver Jubilee 25/50

Postby teknoman2 » 28 Feb 2014, 14:46

I thought making these minor changes on V1 will change somehow the frequency response of SL5.
I know they are major differences between the single ended and the push pull amp.
So do you think buying an Jub is the best scenario?
How much do you think is a reasonable price for a jub 25/50 head?
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Re: Marshall SL 5 mods to Silver Jubilee 25/50

Postby okgb » 24 Sep 2018, 15:32

Yeah , they are very different amps , the SL sounds quite good for that 80's modded marshall thing [ I own one ]
If you're looking for the slash sound , I'm not sure he uses either these days , modded 800's I believe
and because his name is associated with the jubilee's they don't go cheap! , look for best price on the reissues.

one mod I did to my sl5 was adding a passive fx loop , single ended pwr amps can have more hum than p-p types so I can take the pre out into something else
or add fx !
[ I know this post is years old, respond if you see it ! ]
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