Tube measurement question...
I recently upgraded the 300b tubes in my Manley 300b pre-amp. I was running the Shuguang 300b-z treasures and on the recommendation of a friend I decided to try the PSVANE ACME 300b. As many have already reported, my results were similarly positive, with the PSVANE tubes providing more punch, better dynamics and generally an overall better listening experience. My question is regarding the tube measurements. And I think plate current in particular...which I believe is what they are measuring and notating on the outside of the boxes and designating as Ia = xx mA. The box on my Shuguang tubes says 65 mA. My PSVANES measure at 80 mA. I guess I have several questions...first, what does it mean exactly? Is it telling me what the tube is doing or is it describing a limit? Then I guess I'm wondering if the PSVANES, measuring at 80 vs I believe their spec of 60 mA...is that good/bad/or a no care? I'm sure there will be variance in all the tubes produced within a certain tolerance...just wondering at what point, if any, it starts to matter, and in what way...
Apologies if I'm not asking the question properly or if I've left out some other key data needed to respond. Pretty new to tube rolling and since this caught my eye I thought I'd try and learn something...
Thanks..
@bh123 I have a different take on what those numbers mean. If they are handwritten, I would expect them to be a reading taken from a tester, which suggests that the Psvane tube is a bit stronger. All tubes are built to a tube spec, so that if bias is adjustable, they would all be set to the same idle current. The idea of that number meaning anything else from what I'm saying here is a bit terrifying as a manufacturer. It would mean that there's no standard that the tube is built to meet. |
Thanks..so I checked my manual and (copied below) are their notes on calibration...basically no bias to set. I don't hear any volume difference between left and right channel...everything sounds great. I'm still confused now on what these meansurements mean. Since they are handwritten it seems reasonable to assume that they are actual tested measurements of these specific tubes. But what is is measuring? Is it telling me how much current the tubes pull during operation? Or is it telling me something about the limit of the tubes? Is it good or bad that these are measured at 80 mA vs. the tube spec sheet (from PSVANE site) that shows a spec measurement of 60 mA?
CALIBRATION: Each channel is factory-set for 12 dB of voltage gain (1V in = 3.2V out ) via a pair of trimpots located on the main printed circuit board near the headphone jacks. These pots adjust the amount of negative feedback in order to exactly match the gain be�tween both channels. Only 8.5dB of Global Negative Feedback is used which can be con�sidered minimal. Unless you hear a channel-to-channel imbalance after say, changing tubes, you probably do not have to re-trim the levels. There is no other adjustment that needs to be made. There is no bias to have to set |
FWIW here are the specs from the PSVANE ACME 300b site for this tube. I was looking at the below spec for Ia...which is 60 mA...and then looking at the handwritten measurements on the box which said Ia = 80 mA and trying to figure out what that means about my set of tubes...
Heater Static parameter |
