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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
carlsbad2's avatar
carlsbad2
1,602 posts
 

the higher current is a function of the tube design.  So long as your power supply can handle the extra 20mA (it can) there is no issue.

Jerry

bh123 OP
14 posts
 

Thanks, guys, so if I understand correctly then first it's not an issue because my preamp can handle the extra current.  I imagine that if my gear couldn't handle the extra current it would probably blow the fuse.  Also, it sounds like the plate current may be one of the factors influencing sound, and the higher current may be partially responsible for greater dynamics and fuller sound.  

atmasphere's avatar
atmasphere
11,793 posts
 

@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.

bh123 OP
14 posts
 

Thanks...yes, the numbers are handwritten.  The spec sheet that I can view from the PSVANE site says the tubes are 60 mA and the handwritten numbers on the outside of the box say they are actually 80 mA.  But perhaps measuring the tubes under different conditions?

zazouswing
148 posts
 

Those are testing numbers. The bias should be set based on the amp manufacturer’s recommendations. General rule of thumb is you shouldn’t exceed the recommendation, but going lower is OK and prolongs tube life. 

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