Good Morning.

As far as I understand, to "match" tubes,
they must meet these minimum criteria:
No obvious physical defects.
No electrical defects (shorts, gas, microphonics etc.)
GM within single-digit percentages of each other as
measured on a reliable tester that can be calibrated
for GM, such as the TV-7D (GM conversion charts available).
It is also highly desirable that the
manufacture date codes match.

I know there are people who are picky about this small detail
and that small detail, but
is there anything else that is *generally accepted* as
a necessary part of this set of standards?

Thanks very much.

The plate current should also match (within roughly 10% or so), under normal
operating conditions with no signal applied.

Angus

"David L. Stinson" wrote in message
...
Good Morning.

As far as I understand, to "match" tubes,
they must meet these minimum criteria:
No obvious physical defects.
No electrical defects (shorts, gas, microphonics etc.)
GM within single-digit percentages of each other as
measured on a reliable tester that can be calibrated
for GM, such as the TV-7D (GM conversion charts available).
It is also highly desirable that the
manufacture date codes match.

I know there are people who are picky about this small detail
and that small detail, but
is there anything else that is *generally accepted* as
a necessary part of this set of standards?

Thanks very much.

So, for someone still trying to grasp this topic (thanks to the OP) as well,
what are the tangible effects if the tubes do not match?

"tubeguy" wrote in message
...
The plate current should also match (within roughly 10% or so), under
normal
operating conditions with no signal applied.

Angus

"David L. Stinson" wrote in message
...
Good Morning.

As far as I understand, to "match" tubes,
they must meet these minimum criteria:
No obvious physical defects.
No electrical defects (shorts, gas, microphonics etc.)
GM within single-digit percentages of each other as
measured on a reliable tester that can be calibrated
for GM, such as the TV-7D (GM conversion charts available).
It is also highly desirable that the
manufacture date codes match.

I know there are people who are picky about this small detail
and that small detail, but
is there anything else that is *generally accepted* as
a necessary part of this set of standards?

Thanks very much.

Matching bias current for an equal grid, plate and screen voltage for a
self-biased class A amp, or matching Gm at equal bias current and Vp, Vs
conditions, for a fixed-bias amp. Maybe both.
Point being, Gm differences have little effect in class A amps, whereas Gm
is best matched in a class AB amp, where equal voltage swings are more
important. Most are fixed biased anyway (since auto bias is impossible
without compression effects), so differences in grid bias voltage has little
effect until clipping.

Physical appearance only matters for a show amp; date codes (not to mention
the differences in mere printing on the tube!) are for fanatics.

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"David L. Stinson" wrote in message
...
Good Morning.

As far as I understand, to "match" tubes,
they must meet these minimum criteria:
No obvious physical defects.
No electrical defects (shorts, gas, microphonics etc.)
GM within single-digit percentages of each other as
measured on a reliable tester that can be calibrated
for GM, such as the TV-7D (GM conversion charts available).
It is also highly desirable that the
manufacture date codes match.

I know there are people who are picky about this small detail
and that small detail, but
is there anything else that is *generally accepted* as
a necessary part of this set of standards?

Thanks very much.

"mark" wrote in message
...
So, for someone still trying to grasp this topic (thanks to the OP) as
well,
what are the tangible effects if the tubes do not match?

In a self-biased class A amplifier, there will be a DC current in the OPT,
leading to earlier and unbalanced low frequency distortion, basically,
reducing the max. power output below say 100Hz (or 10Hz for a Turner OPT
:P ). As I said before, Gm differences have little effect when both tubes
are always on.

In a class AB amplifier, where one tube turns off during part of the cycle,
it's important that they be matched for Gm because that tube is all alone,
the other isn't there to cover its 'mistake' so to speak. Most class AB
amps are adjustably fixed biased, so differences in grid voltage (to get an
equal bias current and Gm) are inconsequential. However, many commercial
amps used a solidly fixed bias, requiring tubes matched for Gm, Ia and Vg.

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

Tim Williams wrote:

Matching bias current for an equal grid, plate and screen voltage for a
self-biased class A amp, or matching Gm at equal bias current and Vp, Vs
conditions, for a fixed-bias amp. Maybe both.
Point being, Gm differences have little effect in class A amps, whereas Gm
is best matched in a class AB amp, where equal voltage swings are more
important.

Not in a guitar amp. Try it and see.

Most are fixed biased anyway (since auto bias is impossible
without compression effects),

Mmmmmm! Compression! Sweet...

Lord Valve
Glass Hustler

"Lord Valve" wrote in message
...
Not in a guitar amp. Try it and see.

This group deals primarily with hi-fi, and I certainly do. For a guitar
amp, anything goes as far as I can tell. YMMV.

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

Tim Williams wrote:

"Lord Valve" wrote in message
...
Not in a guitar amp. Try it and see.

This group deals primarily with hi-fi, and I certainly do.

Funny, the name doesn't say *anything* about amplifiers.

Just tubes. BTW, junior, I been here for years and years.

For a guitar amp, anything goes as far as I can tell.

That's right, Sparky. Tone rules, not audiophools.


Lord Valve
Tone Chaperone

VISIT MY WEBSITE: http://www.nebsnow.com/LordValve
I specialize in top quality HAND SELECTED NOS and
current-production vacuum tubes for guitar and
bass amps. Good prices, fast service.
QSC amps, RNC compressors, lots of other good stuff!

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Phone orders/tech support after 1:30 PM Denver time at 303-778-1156

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Tim Williams said:

"Lord Valve" wrote:
Not in a guitar amp. Try it and see.

This group deals primarily with hi-fi, and I certainly do. For a guitar
amp, anything goes as far as I can tell. YMMV.

Oh, now you've done it. You're argueing with the Lord himself!
BTW, I disagree with your statement that for guitar amps, anything
goes. How do you think the various brands got famous for their
particular sound?

--
Sander deWaal
Vacuum Audio Consultancy

"Sander deWaal" wrote in message
...
Oh, now you've done it. You're argueing with the Lord himself!
BTW, I disagree with your statement that for guitar amps, anything
goes. How do you think the various brands got famous for their
particular sound?

By letting anything go? ;o) Like I said, I don't care about guitar amps...
just hi-fi

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms