A quick up date:
Got my JJ 300B installed last night.
4 tubes are all factory tested with the same value.
However, at first installation. Bias can't be zeroed. Output is -0.1V even when the pod is turned all the way clockwise and the amp blow fuses when driving hard.
After I swapped V4 and V6, bias can be set to around 0.03V and then it worked fine.
I had only 3 hours on it.
They sound very good right out of the box.
Did not do serious AB comparison as it might get better after broken in.
Basically, I'm pretty happy with it.
First impression: It is pretty balance from low to high. Very good detail.
GL PX300B (similar price) has a little more body in the mid range and less high extension.
PSVan (half the price) is brighter, less body in the mid.
I found the big transformer is significantly hotter than running with PSVan or PX300B tubes.
It is too hot to put my fingers on it for more than a second.
I have not yet measure the temperature or the current through the plate resisters.
I'm wondering if the JJ is running drawing more current at the same bias.
It would be greatly helpful for users, if someone can provide a procedure or instruction on
- How um-matched tubes affect the amp. How far we can go if not matched?
- How to swap tubes to balance out the un-matching.
- I guess V4, V5 shall be matched and V6, V7 shall be matched. Is it less problem if V4/V5 don't match with V6/V7?
- Swapping V4/V5 or swapping V6/V7 doesn't make a difference, correct?