The Orange Amp Mods page

Posted on Feb 6, 2014

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. In the Ampage threads and at

The Orange Amp Mods page
Click here to download the full size of the above Circuit.

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. 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. 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. 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....

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