[rb2013]

Quote:

Oh Ya.... At the moment it's a death trap.
 
I have a very bad habit of dropping my pinky when I'm holding DMM probes.... It never mattered before.... Guess where my pinky landed?   TWICE !
 
It matters.

Is your hair still standing straight up?

 

[rb2013]

Quote:

 
It's not a project where you're going to save dough by building it yourself.  The cost for the challenge and resulting satisfaction is steep.
What a crap shoot...!.   I'm pleased now.
 
Tomorrow I'm off to the water cutters. 
 

I see - thanks for the detailed list.  Still cheaper then a used Woo WA5-LE or a Manley-Neo Classic 300B RC.

 

[sceleratus]

Dang.
 
I spent all day implementing the ECC88 modification, and wouldn't you know…. it sounds awesome.
 
But the bummer is….. I must buy more glass…"must buy more glass, must buy more glass"
 
I'm rock'n the RTC's and wow…..  Gotta git me soma that there Ruskie glass.  And if they blow up…..

 
I laugh at smoke !

 

[BenchmarkGrado]

Dear Tube Rolling Brethren,

What parameters are compared to deem a set of tubes a matched pair?

Thanks,
Mc

 

[ilikepooters]

Quote:

Dear Tube Rolling Brethren,

What parameters are compared to deem a set of tubes a matched pair?

Thanks,
Mc

 
Transconductance are the figures you'll see bandied about on places like ebay, often measured in mA/v or Mmhos, the higher the better, for tubes like ECC88 12.5mA/v would be considered NOS.
 
But these figures mean nothing when you want the left and right channel to be at equal volume. Then gain is factored in to the equation.
 
ECC88 typically has a µ  (or Mu) of 33 but i've had tubes as low as 31 and as high as 35.
 
For me, Gain (Mu) is the most important, i don't care if one tube tests 12 mA/v and the other one only 10.5 mA/v as long as the gain is equal.
 
But i probably don't know schiit, so ignore me 

 

[sceleratus]

pooters is100% correct.
Looking from the 10,000 ft level.
 
These are "dual triode" tubes (I call them valves)  Each tube has 2 triodes.
Different sellers use different pieces of test gear that measure different values.
 
If you are buying 2 tubes there are a pair of measurements for each tube.  One for each triode.
So the seller may say 100/105 for one tube and 110/110 for the other.
You want everything as balanced as possible.
 
If the seller say "Tests NOS" that mean "New Old Stock"
So it could be a 1968 tube that has never been used and thus is NOS.  Those values might be 120 / 120.
Those can be found in the tubes specification sheet published in the 1960's
 
As ilikepooters posted the values the seller states may be from a different piece of gear with different measurements.
Those values can be found on the spec sheet.

 

[BenchmarkGrado]

Thanks,

OK, so Emissions (7.5/7.0 ma) reflects the transconductance of the tube sections and says nothing about the gain, but indicates a used tube with a moderate lifespan? One cannot know the gain from such info? How does one then place a value on this particular tube?

Thanks,
Mc

 

[Lord Soth]

For me, Gain (Mu) is the most important, i don't care if one tube tests 12 mA/v and the other one only 10.5 mA/v as long as the gain is equal.

But i probably don't know schiit, so ignore me 

In theory,
mU = Rp x Gm

mU = Amplification Factor a.k.a "mu" /siemens
Rp = Plate resistance "Rp"/ohms
Gm = Transconductance in umhos


This is based on my personal experience.

I own a customized digital tube tester which can test tubes in the ECC88 family.
My tube tester is unique as it can test such tubes under variable test conditions.

After testing over 300 of such tubes (PCC88, E188CC, E288CC, 6DJ8, CCa, 6922) in my private collection, I can confidently say that the single mA reading from standard test conditions on the tube data sheet can be relied upon.

Why?

The ECC88 tube is very linear in nature, and I suppose this is why it is so popular in audio tube amps.

In other words, if you obtain a mA reading of say 15 at the standard test for 2 tubes, there is a very high probability that they will perform the same at say 12.5 mA under another set of test conditions.

What does this mean to the average audiophile?

If a set of ECC88 tubes is matched at say 15mA (both halves) at standard tube test conditions, the gain is also likely to be the same.
There is no need to worry too much about the gain for small preamp tubes.

Please note that this does not apply to power tubes such as EL34s for e.g. whereby tubes should be matched on gain.

 

[ilikepooters]

Quote:

Thanks,

OK, so Emissions (7.5/7.0 ma) reflects the transconductance of the tube sections and says nothing about the gain, but indicates a used tube with a moderate lifespan? One cannot know the gain from such info? How does one then place a value on this particular tube?

Thanks,
Mc

 
7.0 mA/V i would guess the tube still has circa 60% of its life expectancy remaining, so around 3000 hours for an ECC88 or 6000 hours for an E88CC.
 
Depends how much that listening time is worth to you i guess.
 
Gain is a bit of a lottery unless you can persuade whoever is selling the tubes to match by gain, if they have a tester capable. You can buy your own tester, buy job lots of tubes and test yourself, but this would be expensive.

 

[Lord Soth]

Quote:

Thanks,

OK, so Emissions (7.5/7.0 ma) reflects the transconductance of the tube sections and says nothing about the gain, but indicates a used tube with a moderate lifespan? One cannot know the gain from such info? How does one then place a value on this particular tube?

Thanks,
Mc

 
Again, the Tube data sheet is your friend!
There is a list of readings for New tubes and "End of Life" tubes.
 
If we take the example of the Philips E88CC (SQ) Tube datasheet (can be downloaded from the Internet), under standard Test conditions,
A New tube is listed as
Ia = 15mA
S = 12.5 mA/V
 
An "End of Life" tube has
Ia = 13.5mA
S =  9 mA/V
 
And a "used" tube is listed as
Ia = 14.2 - 15.8 Ia
S = 10.5 - 15 mA/V
 
As a New tube is used, it's readings actually shoot up slightly initially, hence a "used" tube could have higher readings than a completely "new" tube.

 

[mhamel]

So... to add to this and make it a bit more complicated than just reading the data sheet numbers...
 
Recently I picked up a Maxi Preamp digital tube tester/matcher.   It's a great tester, measures transconductance, gain, noise, lets you listen to the tube right through the tester, etc.   When measuring anything in the 6DJ8 family, however, the numbers on it are nothing like what's on the data sheet.   The tester measures along a different point in the tube's curve, which is still valid, but makes the numbers themselves make no sense without plotting out where along the curve it should be.   It took a little getting used to, but it makes me hesitant to put numbers on the tube if I'm selling it, because it's easy to misread as a very low measurement even though it's NOS or better at the point in the curve where it was measured.

 

[BenchmarkGrado]

Therefore, following ilikepooters post, if the tube datasheet indicates that a good tube measures >= 6.5 ma, then ilp's estimate of 3000 remaining of the 6000 hrs expected lifespan should be close for that E88CC equivalent tube. If so, makes sense. The $purchase value then is substantially less than NOS.
How much warmup time do you usually give your tubes before listening to your HPs? Figures into the functional lifespan of the MP.

Thanks, guys
Mc

 

[BenchmarkGrado]

mhamel,

There ideally, should then be a standard test curve and a reference test point on that curve to compare different tube samples. I'd be interested to see some of your output, if it is not too difficult to produce in these pages.

Mc

 

[OldSkool]

Why does the HD650 pair so well with the Amperex orange A-frames? I snagged a pair of orange PQ's on Audiogon last week and just now sitting down to enjoy them.
 
Killer combo, IMO
 

 

[TonyRS]

Anybody with LCD-2's here? 

 
Which tubes compliment the LCD-2 best?