antrecords 7/27/2018 12:23 PM
Orange AD140 10r & Diode Question
Hey guys, I have an AD140 on the bench here. Regarding the power tubes the plate diodes are missing and the 10 ohm cathode resistors are replaced by metal jumpers. It looks clean. The schematics I've seen show them there, as does the pcb. Does anyone know if this is a service update/revision? And if not opinions on replacing the components? Thanks in advance.
The Dude 7/27/2018 6:18 PM
The diodes are for protection. The amp will work fine without them. The 10 ohm resistors missing won't change much either because they are such low value. They may alter bias slightly. I would check your bias anyway. I'm not sure if this is a revision. You could certainly add those parts if you like. The amp will work fine either way.
g1 7/27/2018 6:48 PM
The diodes were also reported as missing here, so it may be the stock condition:
Some have argued that that type of diode protection scheme does have a slight effect on the tone, so perhaps they decided to remove them from the design, or possibly for cost savings if they didn't think they were worth it.
The cathode resistors look like they were set up for the bias test points shown on schematic. Again, they may have figured it was not worth it.
antrecords 7/27/2018 7:10 PM
Thanks Dude and G1, that's exactly what I was wondering. It definitely looks clean, could be factory. I don't think I'm going to mess with it.
nevetslab 7/28/2018 12:03 AM
I believe the metal jumpers are a factory installation. I've encountered them on many of their AD200's, Rockerverbs, others, and usually swap them out with 1 ohm 3W MO resistors, so it's easy to read the cathode current of each tube.
antrecords 7/28/2018 12:05 AM
Thanks nevetslab, I suppose it was cost cutting as mentioned above.