Power Tube Matching


Can someone translate the two #’s on the tube boxes?

What does the first two digit # signify? Plate current I think. And I assume millivolts, milliamps? Or what?

And the 2nd four digit # means transconductance I gather. What is transconductance?

How far apart can these #’s be before they are considered unmatched? And if you explain with percentage, I will need to know how high the numbers go, so maybe stick to actual number increases. My point being, on the internet people just say "5% difference." This means nothing if the plate current numbers can go up to 35 million, or only 100, or maybe 50, or 120.

So, if I Bob has 3 tubes that all have the first number of 14.3.....what numbers on a forth tube would be considered matched? 17.1, 18.4, 19.0, 25.8, or even 12.3?

What happens really if Bob used an unmatched pair of tubes in an amp. And it would be nice to hear about direct experience.

Thank you for your time,

 

TD

 

128x128tonydennison

No don't worry so much about the Ip value , as long as it is the same on all four.   Some places will put a sticker on the base of the tube.  Apex tube matching puts a label on the base of the tube with the value as measured on their equipment.   

I have had pretty good luck with the JJ tubes I have had that were Apex matched.   There are other places that fully test and grade their tubes in a similar way

On your amps if they have an LED for bias will be around 50mA when it starts to glow brightly.    I use this when I retube a 6L6 or EL34 based amp. 

I use this 

https://www.vhtamp.com/avtttt2

It is a great tool for adjusting bias and safe because you are not using meter probes on test pads 

Quicksilver has all of the bias values except the Mid Mono so I asked Mike and he said 53 mA for best performance.   That VHT tool is more accurate than the LED , although it gets you close if set to where it just starts to get bright. 

Gm is expressed in Micromhos and generally the higher the better because it suggests the tube is strong.   No guarantee,  some tubes can drift.  Draw more or less current 

That's why amps with individual bias for each tube or auto bias are more able to cope with mismatch.   

@oddiofyl 

Hey the milliamp tester looks like a good thing to have.

I see one on reverb for $100 new. I'd like to find a used one for $50 or $60. I will look. Thanks.

I'm go to send you an IM.

@tonydennison RAM Tubes is the company founded by Roger Modjeski and run by me since his passing. You can find it here: https://www.ramtubes.com/