OTR 120

[Randy Bass]

Billy has enough stuff...

I thought the missus had hacked your account for a moment...

[Jarkko Mattheiszen]

Bump for an old thread since I stumbled upon here googling my own amp! I've got an OTR and thought I'd share some pics here. This unit actually has a different PCB from the ones I've seen (from what I can tell, it's the 70's OD board, right?) and the chassis seems like old stock, too:









I love the amp, but I'm a sucker for vintage gear and I just can't get the idea of getting a 70's OR120 instead out of my head

[fiveightandten]

Bump for an old thread since I stumbled upon here googling my own amp! I've got an OTR and thought I'd share some pics here. This unit actually has a different PCB from the ones I've seen (from what I can tell, it's the 70's OD board, right?) and the chassis seems like old stock, too:











I love the amp, but I'm a sucker for vintage gear and I just can't get the idea of getting a 70's OR120 instead out of my head

Wow, very interesting. It looks to me like someone pieced together that amp from 70’s and 90’s parts. And the head sleeve is from a relatively modern amp (not original to the chassis, and probably from an AD-140). The serial number is very low and there’s no model number on the back, which is quite curious as well.

The circuit board is indeed from a 70’s amp. Though, at least some of the components on it were in a 90’s amp (presumably original to the chassis). The electrolytics look to have been removed from the OTR board and loaded into that board.

The resistors are 1/4W and not anything that was ever used in any factory Orange head. This is the case for most of the components on that board.

The impedance and voltage selector were lifted from a 70’s amp. The input jacks were lifted from a 70’s amp. The echo loop jacks appear to be on the OTR Echo loop PCB, but I’d say the jacks themselves have been replaced.

Power tube sockets have been rewired a bit, as it looks like all the control grid resistors have been replaced and a few wires here and there.

Do you know if the transformers are original to the chassis? The OT leads don’t look like 90’s/ OTR era Orange transformer leads.

Interesting amp. I wonder what circuit it’s wired up to. It’s tough to tell from a single chassis pic.

[Jarkko Mattheiszen]

Wow, very interesting. It looks to me like someone pieced together that amp from 70’s and 90’s parts. And the head sleeve is from a relatively modern amp (not original to the chassis, and probably from an AD-140). The serial number is very low and there’s no model number on the back, which is quite curious as well.

Yeah, this is a Matamp build, and the serial number #54 says it's one of the very first units to be sold under the Orange name when Cooper got the licence back. From what I've read and found out, it was common for Matamp to use up the old stock of parts they had from the 70's, and being a low serial number, it makes sense.

I have a '76 GT120, and it's almost identical inside except for the modern components of course.

The resistors are 1/4W and not anything that was ever used in any factory Orange head. This is the case for most of the components on that board.

That's true as well, and in a way, it's actually not a factory Orange head - at least not completely. I never found out whether Matamp made them from start to finish, or if Orange did the assembly or something. I'd love to hear from someone who was involved with these, as the Book of Orange doesn't shed any more light on this either.

The impedance and voltage selector were lifted from a 70’s amp. The input jacks were lifted from a 70’s amp. The echo loop jacks appear to be on the OTR Echo loop PCB, but I’d say the jacks themselves have been replaced.

Power tube sockets have been rewired a bit, as it looks like all the control grid resistors have been replaced and a few wires here and there.

I might be wrong here, but in fact, I think the chassis is 70's stock as well. If you look closely, the standby switch is in a socket titled PRE AMP / SLAVE OUTPUT, which along with the prints (Model OR and so on) and the impedance and voltage selectors are identical to 70's OR's.

Do you know if the transformers are original to the chassis? The OT leads don’t look like 90’s/ OTR era Orange transformer leads.

Now, this is a bit of a mystery. The OT is definitely older than the PT. Either the PT was replaced (it looks like a TAD one to me) or the OT is old stock, which would be cool. I think I've got some shots of the transformers as well, I'll see if I can find them.

Damn, now that I'm digging back into this, I'm starting to hesitate selling it again. It's a real oddball and the only one I've ever seen of it's kind.

[Jarkko Mattheiszen]

Ok, here's the PT:



And here's the OT:



A couple more pics I found the original owner sent me:

[Jarkko Mattheiszen]

Now that I'm looking at it again, it's definitely a 70's Overdrive PCB. From what I can tell, everything is pretty much identical to OD's, except for probably some component values as per the OTR schematic, but it looks to me there's a bypass cap on the 220k grid leak resistor, which shouldn't be there. I can't find it in the any of the OR120/OD schematics nor the OTR one. Any idea what's up there?

Edit: Ah, I think it's actually the V1 plate resistor, so the cap is probably there to tame oscillation.

[fiveightandten]

Yeah, this is a Matamp build, and the serial number #54 says it's one of the very first units to be sold under the Orange name when Cooper got the licence back. From what I've read and found out, it was common for Matamp to use up the old stock of parts they had from the 70's, and being a low serial number, it makes sense.

I have a '76 GT120, and it's almost identical inside except for the modern components of course.

That's true as well, and in a way, it's actually not a factory Orange head - at least not completely. I never found out whether Matamp made them from start to finish, or if Orange did the assembly or something. I'd love to hear from someone who was involved with these, as the Book of Orange doesn't shed any more light on this either.

I might be wrong here, but in fact, I think the chassis is 70's stock as well. If you look closely, the standby switch is in a socket titled PRE AMP / SLAVE OUTPUT, which along with the prints (Model OR and so on) and the impedance and voltage selectors are identical to 70's OR's.

Now, this is a bit of a mystery. The OT is definitely older than the PT. Either the PT was replaced (it looks like a TAD one to me) or the OT is old stock, which would be cool. I think I've got some shots of the transformers as well, I'll see if I can find them.

Damn, now that I'm digging back into this, I'm starting to hesitate selling it again. It's a real oddball and the only one I've ever seen of it's kind.

Now that I look at your pictures closer, there are photos of 2 different amps here.

This one is a 90's amp in a modern head sleeve:


And the rear of the amp that's in the rest of your pics does not look like a 70's chassis to me, for a few reasons:
-I've personally never seen a 70's chassis with 120V primary for US mains. They're all 115V.
-All the 70's heads I've seen have 2 small holes drilled to mount a shield around the input jacks and FAC knob. This chassis doesn't have it.
-This is punched for an IEC mains connector. The later 70's amps punched for these connectors typically have a different font and different rear silk screening on the back of the chassis.

OT does look like it could be an old 70's iron. The color coding on the leads looks right for that. I'm not sure what the PT is, as it's epoxy potted with newer bell covers. I'm on my phone, so seeing things in this tiny screen is difficult.

Now that I'm looking at it again, it's definitely a 70's Overdrive PCB. From what I can tell, everything is pretty much identical to OD's, except for probably some component values as per the OTR schematic, but it looks to me there's a bypass cap on the 220k grid leak resistor, which shouldn't be there. I can't find it in the any of the OR120/OD schematics nor the OTR one. Any idea what's up there?

Agreed. No doubt about the PCB, it's 70's.

Are you talking about the pf range film cap soldered to the resistor in the lower right? No, it doesn't look like it's supposed to be there. I don't know the PCB layout of the 70's OR amps all that well, but isn't that the V1 plate resistor (220K) it's bypassing? I thought the 220K grid load was typically standing on the V1 socket. If that cap on the plate, it's bleeding high frequencies off.

Just looking at the components, the lead dress, and the overall build of the amp, I'd be surprised if someone from Matamp wired this up. The leads aren't rolled, shielded wire isn't tucked into the chassis, and the components aren't right. Though it's very curious regardless, as it appears you have quite a rare chassis with a lot of 70's parts loaded into it. I've not seen another like it. It's a pretty cool amp.

It's curious that the master volume can't be wired like a factory OTR, as there are no slots for the .068 caps on the master outputs (wipers). I wonder how that's wired up.

And in the 90's amps, the 3rd stage grid load resistor was typically soldered onto the slave out jack. As that's not there in this amp and it's not a 90's OTR PCB, I wonder where that resistor is.

Thanks for sharing the pics...we don't get to see cool old amps like this around here that often. I"m assuming you have all the schematics off the OAFG, but just in case:
http://www.orangefieldguide.com

I think I may have an original Orange brochure from the late 90's sitting around with the OTR in it. I could probably dig it out and scan it if you're interested.

[Jarkko Mattheiszen]

Well spotted regarding the rear picture, looks like I've messed up the picture folder of my amp and the one with pics of all the other OTR's I found! I'll remove it and take a new one when I get back to the studio. The close up one is from my amp. Thanks for noticing, I actually had that photo in Reverb as well

Regarding the chassis, I think you're right. I've seen some with 110V stamped there, but never one with 100V and then again, I've only seen the non-drilled ones in post-90's units.

For the Matamp point, it's definitely in line with the other 90's Matamp builds I've seen, and I've compared it to a couple other 90's Matamp-built Oranges, and it's the same with those. I'm not an expert on that era of Matamp, but as far as I know, the early comeback production has been confirmed to be them by Orange (please correct me if I'm wrong!), and their build quality at that time wasn't exactly... uh... as refined as it is today or as it was back in the Mathias days Now, this gets me back to the cap! I edited the post right when you were posting, and it is indeed the V1 plate resistor. Seeing that I remembered a friend of mine with a same era reissue having trouble with oscillation before he had it fixed, and a bypass cap at the plate resistor would probably take care of that, right? I suppose this one had the same problem initially.

I'll have to take a closer look at the master volume when I get back to the amp, although I'm afraid it's impossible to see how it's wired without lifting the board first. I'll check the component values while I'm at it and see how much of it fits the OTR schematic by Adrian or if it's closer to the old Overdrive schematic, even though the differences are quite minimal.

Thanks a lot for sharing your knowledge, I've already learned a lot more about this particular amp, and it just keeps getting more interesting! All the other OTR's (and all the other comeback era re-issues too for that matter) have had the new kind of PCB, but then again, I've never seen one with a nearly as low serial number.

[Jarkko Mattheiszen]

This (even though considering the source you can probably guess) is pretty much in line with what's guessed:

"During this era, MATAMP of Huddersfield had just re-opened with it's newly financed owner Jeff Lewis. The first thing Jeffrey did was contact Cliff Cooper and begin the Orange production again. These amps, known to most as the "reissue" Orange. Old Matamp and Orange chassis where used with new and old Orange front panels ranging from OR's to the new OTR panels. Inside the amps where made from Orange VOTW boards/brains and left over transformers."

I had to check, but the grid resistors are actually the same on a Superbass from the same era

[bclaire]

Wow... cool stuff. Finally a thread worth re-opening!

[Jarkko Mattheiszen]

Whaddayaknow, upon further searching, I stumbled upon pics of an identical OTR, only to find out it's actually my amp! Here's the link to his pics:

http://s721.photobucket.com/user/odgeuk ... t=3&page=1

The PT has definitely been swapped and the plate resistor cap added, but otherwise it's exactly the same. Anyone happen to know the guy?

[bclaire]

Whaddayaknow, upon further searching, I stumbled upon pics of an identical OTR, only to find out it's actually my amp! Here's the link to his pics:

http://s721.photobucket.com/user/odgeuk ... t=3&page=1

The PT has definitely been swapped and the plate resistor cap added, but otherwise it's exactly the same. Anyone happen to know the guy?

Wow... has Photobucket gotten annoying with all the ads or what? I could barely see any of the pictures because six ads popped up over them!

Cool amp! How does it sound? And I wonder if those are the Noel Gallagher mods?

[Jarkko Mattheiszen]

Yeah, it has, took me like three refreshes for each photo to see them. The Gallagher mods are very minor, here's both a comparison schematic (not 100% accurate but close) and the original OTR schematic by Adrian:

http://www.orangefieldguide.com/OFG_SCH ... rschem.gif
http://www.prowessamplifiers.com/schema ... rschem.gif

It sounds great, and funnily Oasis is probably the last thing that comes to mind when cranking it The only thing I'm not a 100% happy with is the highest area of the top end. There's something in there that bugs me a bit, although it's only with V30's and only in the room and not miced, and in fact, no-one else hears it even when standing next to me with the amp blazing.

I actually got hold of the guy who took the pics, really cool to find an old owner from way back!

[fiveightandten]

Well spotted regarding the rear picture, looks like I've messed up the picture folder of my amp and the one with pics of all the other OTR's I found! I'll remove it and take a new one when I get back to the studio. The close up one is from my amp. Thanks for noticing, I actually had that photo in Reverb as well

Regarding the chassis, I think you're right. I've seen some with 110V stamped there, but never one with 100V and then again, I've only seen the non-drilled ones in post-90's units.

For the Matamp point, it's definitely in line with the other 90's Matamp builds I've seen, and I've compared it to a couple other 90's Matamp-built Oranges, and it's the same with those. I'm not an expert on that era of Matamp, but as far as I know, the early comeback production has been confirmed to be them by Orange (please correct me if I'm wrong!), and their build quality at that time wasn't exactly... uh... as refined as it is today or as it was back in the Mathias days Now, this gets me back to the cap! I edited the post right when you were posting, and it is indeed the V1 plate resistor. Seeing that I remembered a friend of mine with a same era reissue having trouble with oscillation before he had it fixed, and a bypass cap at the plate resistor would probably take care of that, right? I suppose this one had the same problem initially.

I'll have to take a closer look at the master volume when I get back to the amp, although I'm afraid it's impossible to see how it's wired without lifting the board first. I'll check the component values while I'm at it and see how much of it fits the OTR schematic by Adrian or if it's closer to the old Overdrive schematic, even though the differences are quite minimal.

Thanks a lot for sharing your knowledge, I've already learned a lot more about this particular amp, and it just keeps getting more interesting! All the other OTR's (and all the other comeback era re-issues too for that matter) have had the new kind of PCB, but then again, I've never seen one with a nearly as low serial number.

FYI, you can trace things out pretty easily with the continuity tester function on your DMM and a small flashlight. Put the flashlight under the PCB, and you can see the traces very easily. Use the DMM to find which lugs leads on the underside are soldered to. Though, these PCB's come up very easily and usually have plenty of wiggle room to move it and see on the underside without desoldering anything.

If you find that it deviates from the OTR schematic, you may find this thread helpful. I listed all the differences between the schematics here (there's a link a google sheet with a table of the component values):

viewtopic.php?f=2&t=55823&p=655360&hili ... it#p655360

And yes, that plate bypass cap will definitely roll off high end and might have been put there to quell an oscillation. If it were my amp, I'd consider neatening the wiring and lead dress up a bit to try and solve any oscillations with that cap removed. If you're selling it, you may not want to bother. It appears to be pf range and probably isn't affecting the sound of the amp in a huge way if you're not running high presence or treble settings. Though, I'd bet you'll notice a difference with it removed. You can always add a shield around the inputs. You can trace the oscillation down by searching for AC on the grids to see where it originates. Also, plugging a lead into the inputs and (carefully!) waving that around in the chassis is a great indicator of where noise is lurking in the layout.

Just FYI, the *third* stage plate bypass cap was likely put in the amp to negate oscillation, as most of these amps will oscillate without it. That's a fairly large value and makes a huge difference when you remove it. You could also play with the value of that cap if you can't get the amp stable without this V1 plate bypass cap in there.

Someone has changed some things since the picture you posted from the previous owner:
-It looks like the power transformer has been swapped out since that old pic was taken. The leads I can see are different. The 1st filtering stage and fuse wiring is changed. The bias supply lead is soldered to the top of the board.
-The output transformer has been out. In the older picture there are wires coming through the grommet near the input jacks. Now all of them are coming through one hole. This is the #1 place where these amps oscillate, so they were likely trying to clean that wiring up and get it away from the inputs.
-That black wire running from the input jacks to the top of the PCB wasn't there before. What is this? I looks like it's coming from the tip and going to the V1 cathode resistor (?) In any case, it doesn't look like it should be there, as you do have the shielded line running to the V1 grid (is that shield grounded? It looks like the end of that wire is wrapped in electrical tape now...it wasn't previously).

This (even though considering the source you can probably guess) is pretty much in line with what's guessed:

"During this era, MATAMP of Huddersfield had just re-opened with it's newly financed owner Jeff Lewis. The first thing Jeffrey did was contact Cliff Cooper and begin the Orange production again. These amps, known to most as the "reissue" Orange. Old Matamp and Orange chassis where used with new and old Orange front panels ranging from OR's to the new OTR panels. Inside the amps where made from Orange VOTW boards/brains and left over transformers."

I had to check, but the grid resistors are actually the same on a Superbass from the same era

Interesting. My history is foggy on who made these. I've owned a few OR-80/120 models made in the 90's (and currently have one). I've heard it thrown around that these were made under contract by Trace Elliot, though I've also heard it thrown around that Matamp made them, or made "some of them". Those amps are very clean and tidy builds and very consistent, component-wise.

Anyways, all the OTR amps I've seen look exactly like those builds, which is what surprised me about your amp. Though, with the 70's PCB and all, I think it's clear that it's not the same. Your post above seems to make sense, and what's nice about your amp is that you apparently have the 70's output transformer, but a newer PT. You don't want a 70's PT...my GRO runs nearly 520V on the plates (and more importantly the screens).

[Jarkko Mattheiszen]

Great info, thanks a lot!

FYI, you can trace things out pretty easily with the continuity tester function on your DMM and a small flashlight. Put the flashlight under the PCB, and you can see the traces very easily. Use the DMM to find which lugs leads on the underside are soldered to. Though, these PCB's come up very easily and usually have plenty of wiggle room to move it and see on the underside without desoldering anything.

If you find that it deviates from the OTR schematic, you may find this thread helpful. I listed all the differences between the schematics here (there's a link a google sheet with a table of the component values):

viewtopic.php?f=2&t=55823&p=655360&hili ... it#p655360

Yeah, I'll get into it when I get the chance! I was going by the photos as the amp is not with me right now, but once I get this damn flu out of my system I should have some spare time to bring it home from the studio

And yes, that plate bypass cap will definitely roll off high end and might have been put there to quell an oscillation. If it were my amp, I'd consider neatening the wiring and lead dress up a bit to try and solve any oscillations with that cap removed. If you're selling it, you may not want to bother. It appears to be pf range and probably isn't affecting the sound of the amp in a huge way if you're not running high presence or treble settings. Though, I'd bet you'll notice a difference with it removed. You can always add a shield around the inputs. You can trace the oscillation down by searching for AC on the grids to see where it originates. Also, plugging a lead into the inputs and (carefully!) waving that around in the chassis is a great indicator of where noise is lurking in the layout.

Actually, if anything, the amp is perhaps a bit too bright in top HF range for my liking as is. Then again, it's quick and painless enough to see how it sounds without it, so I might as well give it a go! It was up for sale, but I took it down. It's too interesting to part with just yet!

Someone has changed some things since the picture you posted from the previous owner:
-It looks like the power transformer has been swapped out since that old pic was taken. The leads I can see are different. The 1st filtering stage and fuse wiring is changed. The bias supply lead is soldered to the top of the board.

Yup, this was indeed confirmed when finding the old pics! I'm pretty sure the new PT is this one from TAD, or at least I haven't been able to find anything else suitable that looks identical: http://www.tubeampdoctor.com/en/shop_Ma ... k_MKII_133

-The output transformer has been out. In the older picture there are wires coming through the grommet near the input jacks. Now all of them are coming through one hole. This is the #1 place where these amps oscillate, so they were likely trying to clean that wiring up and get it away from the inputs.

Makes sense. I've now heard of three of these amps, all with the same serious oscillation problems from the factory. Comparing to pics from a friend's Superbass from the same era, the same rerouting has been done to that one.

-That black wire running from the input jacks to the top of the PCB wasn't there before. What is this? I looks like it's coming from the tip and going to the V1 cathode resistor (?) In any case, it doesn't look like it should be there, as you do have the shielded line running to the V1 grid (is that shield grounded? It looks like the end of that wire is wrapped in electrical tape now...it wasn't previously).

That is curious. The point it's connected at the board should be the ground, right? Perhaps they switched the input jack ground there? I'll have to check that, it's hard to tell from the photo!

Interesting. My history is foggy on who made these. I've owned a few OR-80/120 models made in the 90's (and currently have one). I've heard it thrown around that these were made under contract by Trace Elliot, though I've also heard it thrown around that Matamp made them, or made "some of them". Those amps are very clean and tidy builds and very consistent, component-wise.

I might be completely wrong here, but as far as I know, the production of the earliest post-Gibson Oranges were handled by Matamp. I know it should be taken with a grain of salt and it's just additional trivia really, but there are some pretty interesting photos on Wheeler's site like this one showing an OTR faceplate under a Green one: http://www.planetoftheamps.com/orange-a ... atamp.html

Regarding the Trace Elliot connection, I've heard (or read, or imagined, this part of the Orange history really is a jungle, huh?) that the later re-issue and OTR boards as in the "modern" looking ones were made by them, but no-one seems certain if they played other parts in the production. What I do know is that a lot of the Matamp stuff from that era is far from consistent, and they did fancy using parts of old stock mixed with new stuff. I've seen some of the builds and it does remind me of my beloved OTR

Anyways, all the OTR amps I've seen look exactly like those builds, which is what surprised me about your amp. Though, with the 70's PCB and all, I think it's clear that it's not the same. Your post above seems to make sense, and what's nice about your amp is that you apparently have the 70's output transformer, but a newer PT. You don't want a 70's PT...my GRO runs nearly 520V on the plates (and more importantly the screens).

Ha, true!

I actually sent Orange an e-mail about this amp along with the photos. I'm not sure if anyone has the time to check them out or if they even have any records on these, but it's worth a shot!