The Orange Amp Mods page Last update: 10 April 2014

Tech info and Modifications for Orange Amps

DISCLAIMER:
Do not try to modify an amp unless you are really familiar with: LETHAL VOLTAGES, electronics, amp electronics in particular,...
Avoid drilling extra holes and making changes to the chassis and pcbs by all means. This will decrease the value of your amp since you will not be able to restore it to the original state anymore. Make sure to take pictures of the original state of the amp, so you are able to restore the amp back to a working state.
I do not accept ANY liabilities for damage to your amp or to you.

Some tech info...

Bias
Mains
Fuses
Schematics
Tubes
Replacement parts
Mod no0: Removing resistor at input
Mod no1: Adding a standby switch
Mod no2: Opening up your tone
Mod no3: Different Master Vol setup for OD amps
Mod no4: The "Soldano" mod
Mod no5: Power Transformer mod
A few Ampage threads on Orange amps

Bias

In the Ampage threads and at the PlexiPalace BBS I found some people recommending to bias Oranges at 32-34 mA. Amperex recommends about 35 Ma's per tube, but 30-33 if your plate voltage is over 560V.
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Mains

Frequently occurring in the US: the PT is not suited for todays Mains voltages. That is why the tubes get plate voltages that are way too high. The amp doesn't operate at the voltages it was meant to. This may cause early wearing out of tubes. There is also some arcing risk in Oranges which is certainly not improved by these higher voltages. Solution?
No standby switch on vintage versions: since Oranges use SS rectifiers this is certainly one of their weak points. Some people insist on adding a standby switch, others say it's part of the vintage charm not to have it...
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Fuses

Fuses blowing in the US: the voltage ratings on the back of the amps are for UK mains voltages (220-240Volts). Evidently the power consumption of the amp is the same no matter on what mains voltage it is running. Since power consumption equals mains voltage times drawn current, fuses in the US have to be rated higher than in the UK.
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Orange Schematics

Please link to this page, rather than post these schematics on other sites.
I will make a difference here between schematics that are 1.official 2.well known 3.drawn up by friendly Orange fans and donated to this site.

Official Orange schematics

AD15 schematic by Trace Elliott	AD15 main schematic	shared by Richard Dennerline, donated by Sooner
	AD15 front panel wiring	shared by Richard Dennerline, donated by Sooner
	AD15 transformer wiring	by Sooner
AD30 schematic by Trace Elliott	AD30 main schematic	donated by Joseph Hargreaves
	AD30 power supply	donated by Joseph Hargreaves
AD30TC schematic	AD30TC front panel pcb
	AD30 main pcb page1
	AD30 main pcb page2
	AD30 test instructions + ECO's
AD140TC schematic by Trace Elliott	AD140TC main board#1	shared by Joel(Spoonie G), donated by Sooner
	AD140TC main board#2	shared by Joel(Spoonie G), donated by Sooner
	AD140TC front panel	shared by Joel(Spoonie G), donated by Sooner
OTR (factory)	factory OTR schematic!!! (23/9/98)
Rockerverb 50 (factory)	Rockerverb 50 sheet 1
	Rockerverb 50 sheet 2
	Rockerverb 50 sheet 3
Graphic	Graphic'72 schematic
	Graphic'74 schematic

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	Graphic post'74 schematic	NOTE: The rectifier diodes in this schematic are drawn incorrectly. If you are building a clone or refurbishing an amp from this schematic, please follow the rectifier bridge section of one of the other 1970s schematics.
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125MKIII	Hustler 125 MKII schematic
Orange Series Two and Hustler OR135 Schematic	Orange Series Two and Hustler OR135 Schematic

Orange Amp Field Guide schematics

These schematics were drawn up by friendly Orange fans.
Please do not post these schematics on other websites without their consent.

1979 Orange Super Bass Schematic

1979_Orange_SuperBass.pdf

1990s Orange Hustler Combo Schematic

1990s_Orange_Hustler_Combo.pdf

GRO and Reverb schematics kindly provided by Ben Hickmott

GRO	GRO100 preamp	GRO100 power amp	GRO100 power supply
	another GRO100 preamp	another GRO100 power amp	another GRO100 power supply
	OR120 '72 preamp	OR120 '72 power amp	OR120 '72 power supply
	OR120 mid 70s preamp	OR120 mid 70s power amp	OR120 mid 70s power supply
Reverb	Solidstate Reverb Unit

OD	preliminary OD schematic
OTR (P.Lourenco)	OTR schematic of a 2002 OTR amp by Matamp - drawn by Pedro Lourcenco

These schematics were drawn up by friendly Orange fans.
Please do not post these schematics on other websites without their consent.
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Orange Amp Parts

Replacement transformers info from Ampage thread(July 2002)
1. Probably the best place to buy replacement transformers is Matamp. They sell replacement transformers as a set (PT, OT and choke).
2. Orange also sells the AD140 PTs as replacements for the 120s; they are a bit larger but are offered by Orange as excellent replacements for the 120W OTs.
3. Axiom Transformers/Mercury Magnetics sells replacement transformers fro Orange amps and also rewinds original transformers. Check the size of the Axiom/Mercury transformers, they are said to quite large...
4. Rubytubes is German shop that offers a OR120 replacement OT and PT. Follow "Produkte" and then "Ausgangsubertrager Orange 120" for the OT. Follow "Produkte" and "Netztrafo Orange 120..." for the PT. Prices seem reasonable.
Tip by Markus Praemessing
5. Shinrock is a German replacement transformer manufacturer. He has reserved some space for Orange replacement on his sites but no products are mentioned yet.
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Tubes

I will try to put some stuff here about what tubes make an Orange sound right. This is often a personal choice, so feel free to give your opinion too.
David from Seattle on the AD30TC:
I've tube the first channel with a 12AU7 for a cleaner sound and the second channel is a 12AX7. I've not had a single problem with it, it sounds great. It sits next to a 1968 JMI TB retrofit and they complement each other quite well. The Orange is signifigantly darker in tone with a rather tight low end. I've tried just about every damn tube configuration in it and it seems to like Mullard In the gain stage of both channels and Telefunken Smooths in the rest of the preamp stage. RCA el84's have sounded the best in the power half but their becoming harder to find so right now its got EI's in it. For the rectifier it has a NOS Philips that keeps the DC conversion quiet and smooth.
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MODS

WARNING!! MODIFYING ANY TUBE AMP INVOLVES OPENING UP THE AMP AND EXPOSING YOURSELF TO DANGEROUS VOLTAGE LEVELS!! IF YOU ARE NOT EXPERIENCED WITH THE PROPER SAFETY PRECAUTIONS FOR WORKING WITH THESE DANGEROUS VOLTAGE LEVELS, TAKE YOUR AMP TO A PROFESSIONAL TO HAVE THE WORK DONE. THE VOLTAGES INSIDE A TUBE AMP CAN KILL YOU IN AN INSTANT!!! THE DANGERS INSIDE A TUBE AMP ARE REAL AND THEY ARE SERIOUS! IF IN DOUBT, LEAVE THE WORK TO A PROFESSIONAL.

Mod no0: Removing resistor at input

Post '72 Oranges often have an extra resistor (220K) at the input. This resistor limits the gain and isn't really useful.
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Mod no1: Adding a Standby switch

One of the most discussed mods to Orange amps is adding a standby switch, so it has to be in. All modern amps have 'em so it is definitely useful.
For a good understanding: the standby switch enables your tubes to warm up before they get the full 500V on their plates. This increases the life of your tubes.
Nevertheless to wearing of the tubes should not be exaggerated either. But if you only run NOS Mullards, it can be a useful option to put a standby switch in.
DO NOT DAMAGE THE AMP BY DRILLING AN EXTRA HOLE. One suggestion I have read is the addition of the switch in the hole of the Slave Out jack(by Amperex). This way you can still restore the amp if wanted.
Best practice: Remove the Slave Output (rarely used anyway). Put a DPDT switch in. Remove the connection between the High voltage secondary taps of the power transformer and the rectifier. Run two wires from PT to switch and two wires from switch to rectifier. Twist the leads and keep the wires close to the chassis to avoid hum.
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Mod no2: Opening up your tone

Mod suggestion by Amperex
The older graphic amps all have a 1000pF capacitor in parallel with the plate resistor of the third preamp stage. This capacitor is meant to eliminate parasitary oscillations. However the amps mostly tend to function perfectly without this capacitor. Removing this capacitor also means removing extra filtering on the sound. The amps are reported to sound brighter after this modification.
Tip: unsolder one end of the capacitor and put insulating tape around the loose end. This way you can resolder the component if wanted.
Tested on my homebrew Orange: my amp had a clearer, less muffled sound. The cap stays out from now on!
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Mod no3: Different Master Vol setup for OD amps

Mod suggestion by Amperex
The classical Post Phase Inverter Master Volume setup as used in the Orange Overdrives(and also in various Marshall amps) adds some filtering of the sound of the amps. Since the original intent of the Overdrive amps with Master Volume was to have the Graphic sound at lower volume, we can consider this filtering to unwanted.
There are alternative master volume setups that cause less unwanted filtering (or "tone sucking"). Amperex has tested an alternative by Ken Fischer. The simplest way to explain this setup: convert your overdrive back to a graphic schematic but replace the two bias feed resistors by a 250K double pot.
Tested on my homebrew Orange: works fine, but I would advise to use a high quality double pot for optimum results.(what's a couple of euros/bucks compared to your hearing anyway?). Approved!
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Mod no4: The "Soldano" mod

Mod suggestion by Amperex
"One more important point in reference to the orange circuits is that they changed the circuit in '74, and rewired the phase inverter. I suggest to anyone that has a '74 graphic or later, including the overdrive, to switch to the old circuit. It only takes a about a half hour to rewire it, and incidently Mike Soldano use to offer this mod when he was in L.A. and obsessed with Oranges. (he actually still offers it). It really makes the amp more punchy and responsive. The post '72 amps IMO can sound kind of mushy, not as dynamic as the earlier ones."
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Mod no5: The Power Transformer mod

Mod suggestion by Angus Causley
The issue has come up from time-to-time that many of the early Orange amps (and apparently the reissue OR80/120 amps) have a power transformer winding that is designed for US wall voltages measuring in at about 115VAC, as they were in the late 1960s. The problem is that modern US wall voltage is closer to 125VAC today. The end result being a much higher voltage on the secondary of the power transformer - especially on the plate supply of the power tubes. The file below shows how to re-wire the mains transformer using the stock 115VAC lead as neutral and the stock 240VAC lead as the hot lead. The difference between these leads being much closer to the modern US wall voltage of 125VAC. This will bring the plate voltage back down to a more reasonable level as well as bringing the filament voltage closer to 6.3VAC which will make all of your tube filaments last a bit longer.
Power_Transformer_ReWire.pdf
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WARNING!! MODIFYING ANY TUBE AMP INVOLVES OPENING UP THE AMP AND EXPOSING YOURSELF TO DANGEROUS VOLTAGE LEVELS!! IF YOU ARE NOT EXPERIENCED WITH THE PROPER SAFETY PRECAUTIONS FOR WORKING WITH THESE DANGEROUS VOLTAGE LEVELS, TAKE YOUR AMP TO A PROFESSIONAL TO HAVE THE WORK DONE. THE VOLTAGES INSIDE A TUBE AMP CAN KILL YOU IN AN INSTANT!!! THE DANGERS INSIDE A TUBE AMP ARE REAL AND THEY ARE SERIOUS! IF IN DOUBT, LEAVE THE WORK TO A PROFESSIONAL.

Ampage threads concerning Orange amps

These are a few Ampage BBs threads that might be useful for many Orange owners.
Repair & maintenance of an OR 120
Info on comparison of the 3 Graphic schematics
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For comments or other mod suggestions please mail me at submissions@orangefieldguide.com