Re: SACRILEGE! NOS Bull*** Debunked...

Lord Valve wrote: 
Lord Valve Speaketh:

I assembled a collection of NOS and current-production
6L6s; these were all pulled from my inventory, and all
had passed my burn-in and GC procedures prior to being
matched on my proprietary matching rig at identical
test voltages.  A measured plate current of 32 mA was
chosen as the value which could be most consistently pulled
from the available stock; when this was not possible
(twice) the nearest lower PC value was selected.  This
was done to insure that the characteristics of the
tubes were as close as possible, as measured on my test
rig.  14 different quads were available for relative
power output testing.

All 14 of the quads were tested in a 1974 SFTR,
master volume/pull boost type.  All of the
electrolytics in the amp were replaced with
Sprague Atoms or Nichicons.  The PI stage was
blackfaced, but the master volume control was
left in the circuit at the customer's request.
The screen and swamp resistors were all brand
new.  Preamp tubes were four Reflektor/Tung-Sol
12AX7s and two NOS Philips JAN 12AT7WC/6201s.

Signals at seven different test frequencies were
run through the Normal channel, as the Vibrato
channel in pull-boost MV SF Twin Reverbs suffers
from asymmetrical clipping.  Controls were set as
follows:  Volume, 4; all tones, 10; MV full up,
no boost, no reverb, no tremolo.  The filament
hum balance was tuned for minimum hum after the
controls were adjusted as above.

A Raytheon/Sorenson model 500-S vacuum tube
AC line regulator was used to supply power to
the chassis.  This is not a tap-switcher, and
it is highly accurate.  AC line input to the
amp measured 122.60 VAC at idle, and 122.80
VAC at max output (measured just before soft
clipping at 100 Hz.)

Plate voltage was 440.50 VDC, measured with
the tubes set for 18.5 watts static dissipation.
Each quad was biased to 18.5 watts static after
a 10-minute warmup period prior to power testing.

All voltages were monitored with either Fluke
189s or 187s.  The signal generator was a Heath
IG-5218.  The scope was a Leader LBO-310A.  The
load resistor was a non-inductive Dale 250 watt
4-ohm 1% mounted to a large heatsink with fan
cooling.  Voltage across the resistor was monitored
with a Fluke 189, and rounded to the nearest .01
VAC RMS.  The monitored voltage was squared and
the result was divided by the load resistance
to obtain the output power at the seven different
test frequencies.  Measurement in each case was
taken after running the amp to a soft clip and
backing the output down until no flattening of the
peaks/troughs was detectable.  The amp was allowed
to "settle" for one minute at each test frequency
after being adjusted as above prior to recording
the reading.

Readings at the seven test frequencies were added
and then divided by the number of readings in order
to assign the tubes a "rank" as far as overall power
output is concerned.  These tests were performed
in order to debunk the belief (currently held by
many people who ought to know better) that NOS 6L6s
will *always* produce superior power output in any
given situation.  The highest-ranking NOS tube placed
fifth.  Note that the top three are separated by only
a third of a watt in output; this is a dead heat as
far as I'm concerned.  However, the highest beats the
lowest (both from the same company) by twenty watts,
and that *is* significant.


Read 'em and weep:

1) Reflektor/Svetlana 6L6GC -

    100 Hz   -   94.18 WRMS
    250 Hz   -   92.83 WRMS
    500 Hz   -   90.44 WRMS
    1.0 KHz  -   90.25 WRMS
    2.5 KHz  -   89.96 WRMS
    5.0 KHz  -   89.02 WRMS
   10.0 KHz  -   81.97 WRMS

   Average:  89.81

2)  SED/Winged C 6L6GC -

    100 Hz   -   92.16 WRMS
    250 Hz   -   90.82 WRMS
    500 Hz   -   90.72 WRMS
    1.0 KHz  -   90.25 WRMS
    2.5 KHz  -   90.25 WRMS
    5.0 KHz  -   89.40 WRMS
   10.0 KHz  -   82.91 WRMS

   Average:  89.50

3)  JJ/Tesla 6L6GC [1] -

    100 Hz   -   92.93 WRMS
    250 Hz   -   91.58 WRMS
    500 Hz   -   89.40 WRMS
    1.0 KHz  -   91.48 WRMS
    2.5 KHz  -   89.78 WRMS
    5.0 KHz  -   89.30 WRMS
   10.0 KHz  -   81.90 WRMS

   Average:  89.48

4)  Shuguang 6L6GC-M brown base [2] -

    100 Hz   -   89.78 WRMS
    250 Hz   -   89.11 WRMS
    500 Hz   -   89.21 WRMS
    1.0 KHz  -   88.80 WRMS
    2.5 KHz  -   88.27 WRMS
    5.0 KHz  -   87.04 WRMS
   10.0 KHz  -   82.99 WRMS

   Average:  87.89

5)  NOS RCA 6L6GC "blackplate" -

    100 Hz   -   88.08 WRMS
    250 Hz   -   88.17 WRMS
    500 Hz   -   89.21 WRMS
    1.0 KHz  -   90.06 WRMS
    2.5 KHz  -   89.02 WRMS
    5.0 KHz  -   86.58 WRMS
   10.0 KHz  -   76.56 WRMS

   Average:  86.81

6)  NOS Philips 7581A [3] -

    100 Hz   -   90.25 WRMS
    250 Hz   -   87.42 WRMS
    500 Hz   -   85.19 WRMS
    1.0 KHz  -   86.68 WRMS
    2.5 KHz  -   85.66 WRMS
    5.0 KHz  -   84.82 WRMS
   10.0 KHz  -   79.30 WRMS

   Average:  85.62

7)  Reflektor/Tung-Sol 5881 -

    100 Hz   -   87.42 WRMS
    250 Hz   -   88.73 WRMS
    500 Hz   -   86.12 WRMS
    1.0 KHz  -   84.27 WRMS
    2.5 KHz  -   84.00 WRMS
    5.0 KHz  -   84.10 WRMS
   10.0 KHz  -   81.14 WRMS

   Average:  85.11

8)  NOS Sylvania/Mesa STR-415 [4] -

    100 Hz   -   85.56 WRMS
    250 Hz   -   83.63 WRMS
    500 Hz   -   84.46 WRMS
    1.0 KHz  -   82.99 WRMS
    2.5 KHz  -   84.00 WRMS
    5.0 KHz  -   84.64 WRMS
   10.0 KHz  -   79.34 WRMS

   Average:  83.52

9)  NOS GE 6L6GC (clear top) -

    100 Hz   -   84.82 WRMS
    250 Hz   -   83.54 WRMS
    500 Hz   -   83.90 WRMS
    1.0 KHz  -   85.19 WRMS
    2.5 KHz  -   84.18 WRMS
    5.0 KHz  -   82.81 WRMS
   10.0 KHz  -   78.61 WRMS

   Average:  83.29

10) Shuguang/Valve-Arts 6L6GC -

    100 Hz   -   81.90 WRMS
    250 Hz   -   81.90 WRMS
    500 Hz   -   80.28 WRMS
    1.0 KHz  -   81.00 WRMS
    2.5 KHz  -   80.64 WRMS
    5.0 KHz  -   78.06 WRMS
   10.0 KHz  -   76.30 WRMS

   Average:  80.01

11) Shuguang/Ruby 6L6GCSTRM -

    100 Hz   -   83.45 WRMS
    250 Hz   -   77.97 WRMS
    500 Hz   -   80.28 WRMS
    1.0 KHz  -   78.94 WRMS
    2.5 KHz  -   76.65 WRMS
    5.0 KHz  -   71.74 WRMS
   10.0 KHz  -   68.06 WRMS

   Average:  76.73

12) Sovtek 6L6WXT -

    100 Hz   -   76.30 WRMS
    250 Hz   -   76.74 WRMS
    500 Hz   -   76.65 WRMS
    1.0 KHz  -   76.56 WRMS
    2.5 KHz  -   76.12 WRMS
    5.0 KHz  -   76.13 WRMS
   10.0 KHz  -   74.31 WRMS

   Average:  76.12

13) Shuguang/TAD 6L6WGC "shortbottle" -

    100 Hz   -   78.32 WRMS
    250 Hz   -   76.60 WRMS
    500 Hz   -   76.48 WRMS
    1.0 KHz  -   74.40 WRMS
    2.5 KHz  -   74.39 WRMS
    5.0 KHz  -   74.56 WRMS
   10.0 KHz  -   72.50 WRMS

   Average:  75.32

14) Sovtek 5881WXT -

    100 Hz   -   75.43 WRMS
    250 Hz   -   73.36 WRMS
    500 Hz   -   69.14 WRMS
    1.0 KHz  -   70.73 WRMS
    2.5 KHz  -   69.31 WRMS
    5.0 KHz  -   68.95 WRMS
   10.0 KHz  -   61.86 WRMS

   Average:  69.83

Notes:

[1]  An 87K resistance (from a decade box) had to
     be placed in parallel with the bias range
     setting resistor in order to bias the JJ 6L6s
     to 18.5 watts static; in actual operation, the
     range setting resistor would be replaced with
     a much lower value than the parallel network
     used in this test, as the bias control was at
     the lowest negative voltage it could produce
     when the shunt resistance was applied.  This
     is a common problem with this particular JJ tube.

[2]  This is the least expensive tube in the group.

[3]  This is the most expensive tube in the group.

[4]  The Mesa STR-415 was a custom selection from the
     Sylvania STR-387/6L6GC production; it was picked
     to be within Mesa's bias range.

An interesting side note:  it was recently reported on
AGA that the base on the Reflektor/Svetlana 6L6GC was
too small to fit correctly into Fender-style beartrap
clamps.  This is nonsense.  This tube's base is in fact
1/32" greater in diameter than the JJ 6L6GC's, and no
reports of JJs not fitting into Fender clamps have been
seen. The Reflektor/Svet's base is the same size as that
used on the Reflektor/Tung-Sol 5881, which is slightly
larger in diameter than the original Tung-Sol 5881's -
which also fit comfortably into standard Fender clamps.
ALL of the bases discussed above were originally built
for EL34s, as they are exactly the same size as the bases
used on the respective companies' EL34 tubes.  Which,
BTW, *also* fit into Fender clamps with no difficulty.

Mullard Mullahs, Philips Philistines, GE Jihadis, RCA
Ankle Nippers (woof!), Telefunken Tyrants, Siemens
Snobs, Amperex Avengers and other various and sundry
NOS hardliners may now commence shucking and jiving
in a vain attempt to impeach the test results.

Good luck.


Lord Valve
Expert


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Your test bed is not even close to the max spec of the NOS, nor does your test bed approach them.

For example, the nos GE's are not even turned on yet with your 18. watts static dissipation.

TRY 30 Watts plate dissipation as the setting, and run them at a plate voltage of 550 VDC in Ultra Linear configuration for example.

All you did was select a test bed that is friendly to the polished turds, for a momentary test.

Use a 400-PS for the test bed, and you will be doing something of substance by presenting an extreme testing environment.

Then run them till they croak.  Then, post the postmortems.

I'm interested in your power rating at 100 hz, with a 50 Hz added after each 100 hours of continuous full tilt boogie dynamic testing.

Don't worry about the 400-PS crapping out as a test bed either.

<Hell, if you ain't got a 400, throw them in an SVT.>

You didn't even STRESS those SELECTED tubes worth a ***.

Like I said long ago in here,.... when I find a polished turd that ain't a polished turd, I'll let you know.

Post the postmortems from extreme dynamic testing.

THAT, is the bottom line here.




Regards,

Rich Koerner,
Time Electronics.
http://www.timeelect.com


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