Does 5w combo 5C need rebiasing when replacing tubes?
It´s a Class A amp?
Does changing from one wattage to another while the amp is on cause any problems?
It doesn't seem to cause any audio issues besides the obvious change in volume - but will it hurt the lifespan of the tubes or damage any components?
So what's the rule? Choose power level before turning on? Turn down the master volume before changing power levels? Or does it make zero difference?
I've noticed that there is rattling/jangling coming from the amp (not the speaker) when playing notes between low A and C and their respective octaves above. It sounds like it is coming from the EL34 valves - is this due to the way that they are mounted without spring dampers? They have not gone microphonic as far as I can tell, and are otherwise performing as expected, so I feel this is more a mechanical issue with the chassis/mounting, or it's just an undesirable characteristic of the valves themselves. What I'd ideally like to know is, do all Origin 20Cs do this or is this the first anyone has heard about this?
I've removed every external variable there could be, moving the amp to another location and isolating it from floor vibrations in the studio. I've taken the 'amp' out of the cabinet so that I could lightly tap the valves, and check the screws around the supports are not loose. You can generate the rattle (or very similar) just by tapping lightly with the handle of a screwdriver, on both valves. This is what I was expecting if it was just physical vibrations from the speaker causing them to rattle in sypmathy. The rattling sound does not get amplified, so it's not in the audio path.
It's enough to be offputting when tracking/practicing in the studio unless pushing out really high volume so that you can only hear the guitar. I play fairly clean a lot of the time so it is more obvious under those conditions.
Would really appreciate some advice. If the answer is, "It's the same for all and there's not much that can be done..." then ok, I just need to know. That said, I spotted there was some sort of similar issue perhaps on Class 5 amps that a kit was developed for to resolve? I may have misunderstood though.
If there is any further mechanical troubleshooting to be done then please let me know. I wouldn't want to void the warranty status if possible. For what it's worth, I'm a systems and support engineer for a large format mixing console company, so I'm competent enough to poke around as required... just figured someone may have alreday solved this one before I carry on!