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Hi all,
I bought a 1959SLP reissue towards the end of last year from eBay. It came with a 1960AV cabinet that dates from 2006. The seller had it modified with a PPIMV, and he knew that the guy (Ákos Mártonffy of MÁKOS amps in Hungary) had carried out a few circuit mods while he was in there but couldn't detail exactly what he had done.
It's been a really busy 3 or 4 months for me, so I've only had the opportunity to use the amp at home. Besides that, I'm not playing in a band at the moment due to commitments elsewhere getting in the way - so sadly, I have had no opportunities to crank this amp. I live in a small flat/apartment, above a shop, with plenty of neighbours to piss off - not ideal territory for a 100 watter. I have had the master at about 20-30%, but I couldn't go any louder than that. It sounds great though. I prefer the normal input, it doesn't break up as quick and it is full sounding.
When I first received the amp, it was pretty obvious that one or more of the valves were microphonic. So I had that sorted out by my amp tech, with a rebias (37mv as far as I recall). He gave the amp a once over to make sure there was nothing suspect going on and it got the all clear, but he said that there had been a number of modifications to the circuit.. which I already knew.
I had been planning for a while to take the chassis out and trace through the circuit and find out what's going on in there. I always like to understand the amps/pedals/guitars I use. I was jamming with it the other night, and boy, it was bright. Granted, I was plugged in to the high treble input - high sensitivity. I also only had the master about a quarter up, and the channel volume was somewhere around 4. So I realise the bright cap will still be in full effect here. Nonetheless, it inspired me to read about the circuit, and try understand it some more.
The seller provided me with detailed pictures of the circuit before I bought the amp. So this morning, rather than take the chassis out, I thought I would take a look at those pictures and see if I could figure out exactly what has been modified. Looking at the schematic from here or here Prowess Amplifiers - Marshall Schematics (top two are the pre and power section)
1) I can see that the network of capacitors attached to the high treble volume (C4, C5, C15, C17 & C18) have been removed.
2) On the high treble volume pot, there is a 1n/2kv WIMA cap across the wiper and outer lug.
3) C16 has been changed, by the look of things, to a film cap with 222k on the side.. 2n2? I assume that cap was in C15 originally. I've seen 22n there in vintage schematics of Super Leads, and the JH100 as well.
4) As well as that, there are a a couple of 0.047uf WIMA caps - but I can't make out the number on the board to locate them on the schematic. I thought they may be coupling caps or maybe C10 &12?
5) C22 has been removed and bridged - not sure what that was for?
6) R25 and R26 have been removed - but this is where the PPIMV has been installed.
This is all I can see, the V1 cathode remains split as far as I can tell. Would someone with more keen eyes than me have a quick scan over the pictures below to see if they can spot anything that I have probably missed?
I was considering two further modifications. Both on push pull pots, so I can just reverse them without leaving any holes in the chassis. 1) switchable shared/split cathode 2) switchable bright cap. What do you guys think? Reasons? I'm a Hendrix geek, and apparently his amp was shared cathode.. a must have for me, but I'd like the option of switching. Also, I will be using the amp at home.. so I thought that a switch would be useful to go from something like a 560pf to no bright cap - which would tame the highs when I'm playing at home. I thought 560pf would suit me best since I like a dirty blues tone as my main tone (that place between clean and really dirty), right around 4 on the volume on this amp.. so when I'm using the amp at gigging/rehearsal volume, the bright cap is still in use but not as much as say the 1n that is in there now. I play Strats and Jazzmasters by the way. Any other mods you can suggest that I might like? I want to leave it alone as much as possible, but just tweak it a little to suit my gear and style more - Strats, Hendrix.. I'm sure I don't need to say much more! Cheers guys
I bought a 1959SLP reissue towards the end of last year from eBay. It came with a 1960AV cabinet that dates from 2006. The seller had it modified with a PPIMV, and he knew that the guy (Ákos Mártonffy of MÁKOS amps in Hungary) had carried out a few circuit mods while he was in there but couldn't detail exactly what he had done.
It's been a really busy 3 or 4 months for me, so I've only had the opportunity to use the amp at home. Besides that, I'm not playing in a band at the moment due to commitments elsewhere getting in the way - so sadly, I have had no opportunities to crank this amp. I live in a small flat/apartment, above a shop, with plenty of neighbours to piss off - not ideal territory for a 100 watter. I have had the master at about 20-30%, but I couldn't go any louder than that. It sounds great though. I prefer the normal input, it doesn't break up as quick and it is full sounding.
When I first received the amp, it was pretty obvious that one or more of the valves were microphonic. So I had that sorted out by my amp tech, with a rebias (37mv as far as I recall). He gave the amp a once over to make sure there was nothing suspect going on and it got the all clear, but he said that there had been a number of modifications to the circuit.. which I already knew.
I had been planning for a while to take the chassis out and trace through the circuit and find out what's going on in there. I always like to understand the amps/pedals/guitars I use. I was jamming with it the other night, and boy, it was bright. Granted, I was plugged in to the high treble input - high sensitivity. I also only had the master about a quarter up, and the channel volume was somewhere around 4. So I realise the bright cap will still be in full effect here. Nonetheless, it inspired me to read about the circuit, and try understand it some more.
The seller provided me with detailed pictures of the circuit before I bought the amp. So this morning, rather than take the chassis out, I thought I would take a look at those pictures and see if I could figure out exactly what has been modified. Looking at the schematic from here or here Prowess Amplifiers - Marshall Schematics (top two are the pre and power section)
1) I can see that the network of capacitors attached to the high treble volume (C4, C5, C15, C17 & C18) have been removed.
2) On the high treble volume pot, there is a 1n/2kv WIMA cap across the wiper and outer lug.
3) C16 has been changed, by the look of things, to a film cap with 222k on the side.. 2n2? I assume that cap was in C15 originally. I've seen 22n there in vintage schematics of Super Leads, and the JH100 as well.
4) As well as that, there are a a couple of 0.047uf WIMA caps - but I can't make out the number on the board to locate them on the schematic. I thought they may be coupling caps or maybe C10 &12?
5) C22 has been removed and bridged - not sure what that was for?
6) R25 and R26 have been removed - but this is where the PPIMV has been installed.
This is all I can see, the V1 cathode remains split as far as I can tell. Would someone with more keen eyes than me have a quick scan over the pictures below to see if they can spot anything that I have probably missed?
I was considering two further modifications. Both on push pull pots, so I can just reverse them without leaving any holes in the chassis. 1) switchable shared/split cathode 2) switchable bright cap. What do you guys think? Reasons? I'm a Hendrix geek, and apparently his amp was shared cathode.. a must have for me, but I'd like the option of switching. Also, I will be using the amp at home.. so I thought that a switch would be useful to go from something like a 560pf to no bright cap - which would tame the highs when I'm playing at home. I thought 560pf would suit me best since I like a dirty blues tone as my main tone (that place between clean and really dirty), right around 4 on the volume on this amp.. so when I'm using the amp at gigging/rehearsal volume, the bright cap is still in use but not as much as say the 1n that is in there now. I play Strats and Jazzmasters by the way. Any other mods you can suggest that I might like? I want to leave it alone as much as possible, but just tweak it a little to suit my gear and style more - Strats, Hendrix.. I'm sure I don't need to say much more! Cheers guys
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