[bcowen]

.

 

[Ripper2860]

Thanks, but I'll just keep outsourcing my tube testing.

 

[Zachik]

I've been a bad, bad boy ...

I snagged a couple of strong and supposedly pretty well balanced Sylvania 6SN7GT tubes with an 052 (1950) year code. (I know, but I scored them at $15.00 for the pair.)

$15 for a pair is practically free! So you were not really a bad boy today... On the other hand - I was, spending $60 on a single Ken Rad VT-231...

I'm a COLLECTOR, dammit!!

Yeah... I am starting to become a collector, too. My wallet is not a happy camper...

 

[Zachik]

Any thoughts on using Pelican 1085 Laptop Case With Foam (https://www.amazon.com/dp/B006C21MCU/) for storing tubes (with or without boxes)?
I think internal depth is sufficient (approx. 2 inches). Probably can store 10-12 tubes in it... Thoughts?!

 

[Ripper2860]

$15 for a pair is practically free! So you were not really a bad boy today... On the other hand - I was, spending $60 on a single Ken Rad VT-231...


Yeah... I am starting to become a collector, too. My wallet is not a happy camper...

$60 for a good VT-231 KR tube is practically free, as well!! OK -- maybe not practically free, but a very good deal.

 

[Zachik]

Being a relatively tube newb, a question for the experts here:
when I see a tube with Test Values: 21xx / 25xx (out of 2600 for new)... what does it mean?!
Does that imply left and right channels would be imbalanced?! Or for Lyr3 which is a non-balanced amp it does not mean anything?

 

[ProfFalkin]

How about... Tubus XII Gradus Programmata... Supremus?


No, too long. Hmm... well, I'm sure we will think of something.

 

[ProfFalkin]

Being a relatively tube newb, a question for the experts here:
when I see a tube with Test Values: 21xx / 25xx (out of 2600 for new)... what does it mean?!
Does that imply left and right channels would be imbalanced?! Or for Lyr3 which is a non-balanced amp it does not mean anything?

Ok... here is where the term balanced gets used in different ways, and has absolutely no relation to each other.

Read this: http://vrps.org/documents/Gm vs mu.pdf

Here are some important bits from that article. Talking about GM or MU in tubes...

... the exact mathematical definitions are in terms of things developed in calculus courses, called partial derivatives.

Gm is the ratio between the plate current change and the grid to cathode voltage change with plate to cathode voltage held constant. If we call Ip the plate current, and Vg the grid voltage, then

Gm = dIp / dVg

where you may read the "d" as "small change in". Another way to read it is as "The small AC plate current resulting from a small AC grid voltage, with the plate voltage held constant, or short circuited for AC" (like by bypassing the tube with a huge capacitor).

If you know calculus, then it means the partial derivative of plate current with respect to grid voltage. Its unit is that of current divided by voltage, or the mho or Siemens, and it is a sort of "conductance". Since this "conductance" is from the input to the output circuits of the tube, and goes "across" the tube, it is called "transconductance" or "mutual conductance". Since "G" is the symbol used in electronics for conductance, this explains the use of the symbol "Gm". It is not a real conductance in any sense of the term. In the fictional mathematical model, this is a single constant. With a real tube it depends on plate voltage, plate current, tube temperature, frequency of the signal, mood of the operator, etc.

Now mu is defined similarly, but it is a ratio of voltages

mu = dVp / dVg

This is the AC voltage gain for small signals, being the AC voltage in the plate divided by the AC voltage on the grid, with the plate current held constant. It has no unit, being a pure number. In the fictional model, this also is a single fixed constant for any given tube. For the mathematically inclined, it is the partial derivative of the plate voltage with respect to the grid voltage. Now, also in the fictional model, there is an effective plate resistance associated with the tube, usually denoted by Rp. By definition,

Rp = dVp / dIp,

in other words the AC voltage on the plate divided by the AC current through the plate.

Thus we have that mu = Gm x Rp

That's why, in an earlier message, I said that Gm and mu are effectively the same. They are essentially proportional to each other. Well, not exactly of course. Gm is a conductance, and mu is a pure number. But in the fictional model Rp is *also* a constant (for any given tube, that is), so there you are.[1]

Now, mu is easier to measure, at least approximately, so that is what "transconductance testers" usually measure. A small AC voltage is placed on the grid of an otherwise appropriately biased tube, and the AC voltage on the plate is displayed, perhaps divided by the (fixed) AC grid voltage, giving an approximation to mu.

Ok, did you get all that? GREAT! Now throw it all out the window, because you don't need it. (I'm a jerk, I know.) The Lyr 3 will automatically balance differences between triodes, ensuring that there is no mismatch in volume. This is called Auto Bias.

Now... let's talk about balanced as it relates to amplifiers. The term "balanced" can be used in two ways, generally speaking. The first relates to the interconnects, and the second to the design or topology of the amplifier itself.

Where it relates to the interconnects (the cable connecting DAC to amp) two "balanced" cables are used to transfer the stereo signal. The real secret here is that these cables have dedicated shielding and grounding which are completely separate from the audio signal and amplification system. Any noise that does make it into the cable won't matter due to the way that the audio signal is being passed through it. That makes them practically immune to noise like RF and EMI. It also doubles the number of wires required to pass the signal. If you want to know how this works, do some Google searches for "Differential Signal Audio" and "Common Mode Rejection". This is a good video explaining the differences in cables, but it doesn't touch on exactly how the noise is rejected. If you want more info, watch this 4 video series.

When someone says "balanced amp", it can be very misleading. The amp might have balanced audio cable connections, but is the internal amplifier topology of the amplifier itself discretely balanced? Often times, I would bet it is not. For the amp to be completely balanced, it would need four (yes, four) discrete amplifiers inside - one for each of the following signals: Left +, Left -, Right + and Right -. This one is easier to find information about, so I'll let you do research on "Fully Balanced Amplifier Design", "Dual Mono" and other such terms.

Or, for a general summary on all of the above, just go read this.

 

[Zachik]

Being a relatively tube newb, a question for the experts here:
when I see a tube with Test Values: 21xx / 25xx (out of 2600 for new)... what does it mean?!
Does that imply left and right channels would be imbalanced?! Or for Lyr3 which is a non-balanced amp it does not mean anything?

The Lyr 3 will automatically balance differences between triodes, ensuring that there is no mismatch in volume. This is called Auto Bias.

Sooooo........... bottom line is said tube should work just fine when used in my Lyr3 ?

 

[ProfFalkin]

Sooooo........... bottom line is said tube should work just fine when used in my Lyr3 ?

Yes. You won't want a tube where the triodes show more than about a 20% difference. Auto bias can only do so much. 21xx/25xx listed on the tube you mentioned is just fine.

 

[ProfFalkin]

Crap. Ebay seller sent me the wrong tube. I usually despise the return process, but we'll see how it goes. The hunt for a backup WH-D continues.

 

[Ripper2860]

That just plain sucks.

 

[Wes S]

Crap. Ebay seller sent me the wrong tube. I usually despise the return process, but we'll see how it goes. The hunt for a backup WH-D continues.

Bummer! I have an open case with ebay at the moment, because my 2 BadBoy's have not even shipped and I paid 7 days ago. Got to love sellers on Ebay!

 

[ilikepooters]

Bummer! I have an open case with ebay at the moment, because my 2 BadBoy's have not even shipped and I paid 7 days ago. Got to love sellers on Ebay!

Seller probbly gone on vacation, hate it when they do that. Why can't they make the listing end nearer to when they can post stuff?

 

[bcowen]

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