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I've had a 1996 1959SLP for a few years now; it came to me already modified, albeit badly, so I figured why not go to town..
I've modified the amp to '68 (roughly) specs slowly over the years. No master volume mod (I removed that recently in favour of a TAD Silencer). The last thing I did was to lower the filtering to '68 spec. For all intents and purposes, the circuit is identical to a '68 Lead - but with a couple of necessary tweaks as you will see.
The amp does sound great.. but it's not quite there yet - I have been using a Firebird with vintage style 'bird pickups (pots are 250k's) for a while now and everything is just a little too bright for my taste.. it's right on the cusp of being ok.. so I'm looking for some minor tweaks to just shave off a little top end. I recently upped the 47pf cap across the PI to 200pf, which was a subtle but noticeable improvement. I've upped the swamp resistors to 10k, which helped a little too. So I don't want to alter the character of the amp by changing things too much - just subtle little tweaks.
I like the nature of the breakup with the presence dimed for example, but it's ear bleedingly bright with my Firebird that way.. so I'd like to get it to a point where I can make more use of the EQ and presence in a positive way.. rather than just backing off the treble and presence all the time.
I wondered about upping the 2n2 coupler on the normal channel to 3n3 or 4n7, plus upping the couplers after the PI to 33nf or 47nf. I'd thought about adding another small value cap (50-200pf) from grid to plate of V1 like the old Sovtek MIGs do.
One thing I did notice last time I was inside - the heater voltages were on the low side <6v.. around 5.6v if I remember correctly. There isn't much I can do about that I suppose, but I have wondered if that has any negative effect? The amp sounds full, the bottom end is as you would imagine - huge, almost too much. The bass control is a typical Marshall on or off switch.
What do you guys reckon?
I've modified the amp to '68 (roughly) specs slowly over the years. No master volume mod (I removed that recently in favour of a TAD Silencer). The last thing I did was to lower the filtering to '68 spec. For all intents and purposes, the circuit is identical to a '68 Lead - but with a couple of necessary tweaks as you will see.
The amp does sound great.. but it's not quite there yet - I have been using a Firebird with vintage style 'bird pickups (pots are 250k's) for a while now and everything is just a little too bright for my taste.. it's right on the cusp of being ok.. so I'm looking for some minor tweaks to just shave off a little top end. I recently upped the 47pf cap across the PI to 200pf, which was a subtle but noticeable improvement. I've upped the swamp resistors to 10k, which helped a little too. So I don't want to alter the character of the amp by changing things too much - just subtle little tweaks.
I like the nature of the breakup with the presence dimed for example, but it's ear bleedingly bright with my Firebird that way.. so I'd like to get it to a point where I can make more use of the EQ and presence in a positive way.. rather than just backing off the treble and presence all the time.
I wondered about upping the 2n2 coupler on the normal channel to 3n3 or 4n7, plus upping the couplers after the PI to 33nf or 47nf. I'd thought about adding another small value cap (50-200pf) from grid to plate of V1 like the old Sovtek MIGs do.
One thing I did notice last time I was inside - the heater voltages were on the low side <6v.. around 5.6v if I remember correctly. There isn't much I can do about that I suppose, but I have wondered if that has any negative effect? The amp sounds full, the bottom end is as you would imagine - huge, almost too much. The bass control is a typical Marshall on or off switch.
What do you guys reckon?
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