Power Tube Matching

It 's name is some what of a misnomer , not a "tube tester "  more of a  ias adjustment tool.   Not something you'll use a lot but it is a great tool

IP is plate current , Gm is transconductance .

In your Mid Monos you need matched tubes unless they are the latest version with a trim pot for each tube’s bias.

Bob only has three matched tubes.... if you put one that isn’t close then one amp will have a tube that is not biased correctly because the two power tubes share a bias pot . One will draw more current than the other , not what you want in a Push / Pull amp.

IP plate current is what you are adjusting. It’s basically a math formula that relates to the plate voltage and how much current the tube will / should draw

Your amp has a plate voltage of something like 440 volts. Mike at Quicksilver recommends setting the bias at 53 mA.

You can’t achieve that if both tubes are not electrically " the same" with respect to their current draw. . Quicksilver strongly recommends matched power tubes for best and safe operation.

When you buy a QS product new the tubes are hand matched on their equipment and are very tightly matched. Looking at a pair of EL84 and the current draw is hand written on each box. 24.1 and 24.0. That’s how tightly matched they should be. Those were from their Headphone amp that has no adjustment, it’s Auto Bias so technically they don’t need to be matched . But they do it on all of their amps

Transconductance or Gm is how strong the tube’s emissions are .

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.   

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. 

The VHT tools a good way to measure the bias of each tube of your mid mono 

When you adjust the bias with this in place it will confirm whether the tubes are close.   It will also help troubleshoot ....  if you try to bias and one socket is too high or too low with a few different tubes it would suggest a bad bias resistor or something else going on with that socket .