JCM 900 (DR) - Any difference from early to late production?

[fitz]

Looking at a 1990 serial # (Y) model 4501 DR 1x12, and wondering if there are any notable differences between older and newer 900's.
From what I can find, they were made between 1990 and 1999, so this one's 1st year AFAIK.
Anything from early releases that should be avoided, or sought after?

 

[Gutch220]

Looking at a 1990 serial # (Y) model 4501 DR 1x12, and wondering if there are any notable differences between older and newer 900's.
From what I can find, they were made between 1990 and 1999, so this one's 1st year AFAIK.
Anything from early releases that should be avoided, or sought after?

There are a couple threads that go into this a bit more. You should read up on these first.
There are some circuit differences throughout the run including the power tubes uses, resistor values in some location, capacitor values in some spots, potentiometer values, transistors, etc.

https://www.marshallforum.com/threads/jcm900-pre-amp-schematic-difference.134559/

Early JCM 900 4100. Serial # Y11174. Is this amp a prototype?

I bought this amp from Jim Marshall and his entourage at Carlsboro Music in Sheffield UK in 1990. I was in a band called Strongheart and our manager was very persistent. Jim’s guys did not want to sell it because they only had two and were on a music store tour to promote the 900 prior to it’s...

www.marshallforum.com

Basically, for the Dual Reverb 900's there are 2 versions of an early schematic that are unknown to have ever been released to the public, they've never been discovered and may or may not even have existed. They'd likely be pre-March 1990.

They also mixed-up circuits ALL THE TIME. They had British versions, SEMKO versions, Canadian versions, USA versions. Many of the circuits are similar similar with only slightly different values of some components and/or some extra fuses early in the circuit, etc. But there was not really uniformity at all times. I for example have a 1990 'USA' version of a 4100, but there are obvious SEMKO locations in the circuit based on component's value differences. I could post them, but I forget off hand. But you can examine the schematic differences AND spot the differences AND then look at your own amp to see where it stands. I think this might be a reason why a group of the same amp can all have slightly different sounds.

I think the main difference early on is the EL34 tubes in the first couple years, then the switch-over to the 5881 power tubes in the mid-90's. Many people like the early EL34 versions.

 

[fitz]

There are a couple threads that go into this a bit more. You should read up on these first.
There are some circuit differences throughout the run including the power tubes uses, resistor values in some location, capacitor values in some spots, potentiometer values, transistors, etc.

https://www.marshallforum.com/threads/jcm900-pre-amp-schematic-difference.134559/

Early JCM 900 4100. Serial # Y11174. Is this amp a prototype?

I bought this amp from Jim Marshall and his entourage at Carlsboro Music in Sheffield UK in 1990. I was in a band called Strongheart and our manager was very persistent. Jim’s guys did not want to sell it because they only had two and were on a music store tour to promote the 900 prior to it’s...

www.marshallforum.com

Basically, for the Dual Reverb 900's there are 2 versions of an early schematic that are unknown to have ever been released to the public, they've never been discovered and may or may not even have existed. They'd likely be pre-March 1990.

They also mixed-up circuits ALL THE TIME. They had British versions, SEMKO versions, Canadian versions, USA versions. Many of the circuits are similar similar with only slightly different values of some components and/or some extra fuses early in the circuit, etc. But there was not really uniformity at all times. I for example have a 1990 'USA' version of a 4100, but there are obvious SEMKO locations in the circuit based on component's value differences. I could post them, but I forget off hand. But you can examine the schematic differences AND spot the differences AND then look at your own amp to see where it stands. I think this might be a reason why a group of the same amp can all have slightly different sounds.

I think the main difference early on is the EL34 tubes in the first couple years, then the switch-over to the 5881 power tubes in the mid-90's. Many people like the early EL34 versions.

I'm assuming the one listed is an EL34 version - pic shows 6CA7's.
Doesn't look like some kind of rare unicorn prototype.
No gut shots, and the current owner "got it from a friend" - per some site messaging.
Thanks for the info & thread link.

 

[cjs42079]

I’ve owned a 4100 DR from 96/97. It has 5881’s stock, but I had it converted to EL34’s. I don’t understand the hate for this amp. I’ve spent a lot of money on Marshall’s since then, but the 900 hangs up there with the best of ‘em. Two channels, passable reverb, good fx loop, 100w MV setup allows for plenty of headroom, and it gobbles up pedals.

 

[fitz]