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Tom Schlangen
 
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Default ECL86/6GW8/PCL86/14GW8 pentode section triode strapped data

Gentlemen,

ECL86/6GW8 or PCL86/14GW8 pentode section triode strapped data now
is available he

http://www.tubes.mynetcologne.de/roe..._as_triode.pdf

As usual, three samples (Mullard 6GW8, ITT/SEL mil spec PCL86,
EI PCL86) were measured and the data was averaged.

While ECL86 gets scarce nowadays, the 300mA heater versions
PCL86/14GW8 still are plenty and cheap, even from "top" brands.

The triode section of this tube is exactly 1/2 of ECC82/12AX7
(nitpickers will say 1/2 of ECC808, with even better data).

The triode strapped pentode section is very linear, it is almost
identical to triode strapped EL84/6BQ5, except that the allowed Pd
is a bit lower (9 watts instead of 12).

Like triode strapped EL84/6BQ5, the trioded pentode section of this
tube will make a bombastic SE driver stage or PP "power LTP"
splitter/driver stage.

Two of them will make a complete front end even for the most swing
demanding PP output tubes: For example use the triode sections as
a diff amp input/splitter stage, and the trioded pentodes as sort
of diff amp / driver like the third stage in the Williamson.

The combined gain of the sections is very high (expect easily up to,
say, 500 times in real world apps). Thus take care to prevent
parasitic oscillations ...

Here is a tip I got from an old HAM: Have a close look how the
sections are wired to the base pins and you will see, that using
a very tiny earthed metal sheet at the socket at the right place,
acting as a static shield, would .... ;-)

Tom

--
When in doubt, use brute force.
- Ken Thompson
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Patrick Turner
 
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Tom Schlangen wrote:

Gentlemen,

ECL86/6GW8 or PCL86/14GW8 pentode section triode strapped data now
is available he

http://www.tubes.mynetcologne.de/roe..._as_triode.pdf

As usual, three samples (Mullard 6GW8, ITT/SEL mil spec PCL86,
EI PCL86) were measured and the data was averaged.


Thanks Tom.

The Ra = 2.5k at Ia = 30 ma, Ea = +300v,
u = 14.3, so gm = 5.72 mA/V.

( 6BQ5 triode u = 20, Ra slightly less.)

1/2 12AX7 are not regarded as good triodes any more these days for
power amps but they work OK in these tubes in a circuit like the one at
http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm

Patrick Turner.





While ECL86 gets scarce nowadays, the 300mA heater versions
PCL86/14GW8 still are plenty and cheap, even from "top" brands.

The triode section of this tube is exactly 1/2 of ECC82/12AX7
(nitpickers will say 1/2 of ECC808, with even better data).

The triode strapped pentode section is very linear, it is almost
identical to triode strapped EL84/6BQ5, except that the allowed Pd
is a bit lower (9 watts instead of 12).

Like triode strapped EL84/6BQ5, the trioded pentode section of this
tube will make a bombastic SE driver stage or PP "power LTP"
splitter/driver stage.

Two of them will make a complete front end even for the most swing
demanding PP output tubes: For example use the triode sections as
a diff amp input/splitter stage, and the trioded pentodes as sort
of diff amp / driver like the third stage in the Williamson.

The combined gain of the sections is very high (expect easily up to,
say, 500 times in real world apps). Thus take care to prevent
parasitic oscillations ...

Here is a tip I got from an old HAM: Have a close look how the
sections are wired to the base pins and you will see, that using
a very tiny earthed metal sheet at the socket at the right place,
acting as a static shield, would .... ;-)

Tom

--
When in doubt, use brute force.
- Ken Thompson


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Tom Schlangen
 
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Hi Patrick,

The Ra = 2.5k at Ia = 30 ma, Ea = +300v,
u = 14.3, so gm = 5.72 mA/V.


thank you for adding this data. May I include
it as an example in the sheet?

( 6BQ5 triode u = 20, Ra slightly less.)


I agree on 6BQ5 Ra (say, 2k), but I have a hard
time to get mu in excess of, say, 15 from trioded
6BQ5. But I don't nitpick: Be it 15, 17,5 or
20 under optimal circumstances, it doesn't matter
much under real world circuit conditions.

1/2 12AX7 are not regarded as good triodes any more
these days


Probably it just ain't "fashionable" nowadays :-)

On the other hand, the absurd prices (of certain
brands) on Ebay tell another story.

Personally, I never used 12AX7 in a DIY project myself,
I admit. No hard reasons, but my finger just automagically
grab an octal based 6SL7 out of the drawer when highish mu
is needed.

Tom

P.S: Next on the bench probably will be triode strapped
EF184/6EJ7 frame grid pentode.

--
The opposite of a correct statement is a false statement. But the
opposite of a profound truth may well be another profound truth.
- Niels Bohr
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Patrick Turner
 
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Tom Schlangen wrote:

Hi Patrick,

The Ra = 2.5k at Ia = 30 ma, Ea = +300v,
u = 14.3, so gm = 5.72 mA/V.


thank you for adding this data. May I include
it as an example in the sheet?

( 6BQ5 triode u = 20, Ra slightly less.)


I agree on 6BQ5 Ra (say, 2k), but I have a hard
time to get mu in excess of, say, 15 from trioded
6BQ5. But I don't nitpick: Be it 15, 17,5 or
20 under optimal circumstances, it doesn't matter
much under real world circuit conditions.


The u of all the EL84/6BQ5 I have tested had u = 20.
Circuit gain was about 18,19 with high value RL.

See the 2.5 Mb of data from STC at

http://www.retrovox.com.au/STC6BQ5.pdf

The triode curves there show the gain with CCS load is 18.2 at 20 mA Ia,
and 20 at 40 mA.
Samples I tested were Sovtek and other Oz made tubes and they went u=20
at 14 mA.

These EL84 are extremely linear with a CCS load.





1/2 12AX7 are not regarded as good triodes any more
these days


Probably it just ain't "fashionable" nowadays :-)


OK in preamps. But the " in brigade " likes more in everything,
so all triodes are expected to have high current, high gm and low Ra,
regardless of where
they are used, but it does not necessarily follow that the sound will be
better
and the measurements are better.

The 12AX7 was a cheap high gain signal triode invented at a time
when the need for such a creature came with demand for electronic
equipments to do more than
just put a radio voice on the mantle piece.
I think they were used even in V2 rockets in WW2.



On the other hand, the absurd prices (of certain
brands) on Ebay tell another story.

Personally, I never used 12AX7 in a DIY project myself,
I admit. No hard reasons, but my finger just automagically
grab an octal based 6SL7 out of the drawer when highish mu
is needed.


I have used 12AX7 often, and they are great for the first stage of a
phono amp for
MM. Hopeless for a low output MC; you need the step up tranny, or
a 6C45pi, but then ppl argue about what sounds best....

I have only used 6SL7 in the front end of SEUL amps, with
6SL7 or ECC35 for V1, ECC32 or ECC33 for V2, and then 13E1 for output.
I had to pick through the SLs though to get a quiet one.

I'll have to work more at training my finger to be automagical.



Tom

P.S: Next on the bench probably will be triode strapped
EF184/6EJ7 frame grid pentode.


There must be 100 tonnes of EF80 or 6BX6 lingering forgotten and
unwanted around the world.
Many were made for the TV IF stages of tube TVs.
But they make fabulous triodes, imho.

Any chance of doing a test on those?

Patrick Turner.



--
The opposite of a correct statement is a false statement. But the
opposite of a profound truth may well be another profound truth.
- Niels Bohr


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Tom Schlangen
 
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Hi Patrick,

There must be 100 tonnes of EF80 or 6BX6 lingering
forgotten and unwanted around the world.
Many were made for the TV IF stages of tube TVs.
But they make fabulous triodes, imho.

Any chance of doing a test on those?


I don't have a single one in the drawer, but that
might change soon ;-)

I'll do the test after having obtained a few.

Tom

--
Falling in love is a lot like dying.
You never get to do it enough to
become good at it.


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robert casey
 
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There must be 100 tonnes of EF80 or 6BX6 lingering forgotten and
unwanted around the world.
Many were made for the TV IF stages of tube TVs.
But they make fabulous triodes, imho.

Any chance of doing a test on those?


Just be sure that you use "sharp cutoff pentodes".
Some TV IF pentodes were "remote cutoff". Variable
gain depending on bias. Great way to do AVC, but
not good for audio work.

Some TV tubes were "dual control" pentodes, and
heptodes (pentagrid). One could use one grid
to feed audio, and the other grid to vary the
gain via a DC bias of the plate circuit.

http://pw2.netcom.com/~wa2ise/radios/elvctube.jpg
http://pw2.netcom.com/~wa2ise/radios/6be6vol.html
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Gregg
 
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Behold, robert casey signalled from keyed 4-1000A filament:



There must be 100 tonnes of EF80 or 6BX6 lingering forgotten and
unwanted around the world.
Many were made for the TV IF stages of tube TVs. But they make fabulous
triodes, imho.

Any chance of doing a test on those?


Just be sure that you use "sharp cutoff pentodes". Some TV IF pentodes
were "remote cutoff". Variable gain depending on bias. Great way to do
AVC, but not good for audio work.


Hi Robert,

Why is that anyway?

--
Gregg t3h g33k
"Ratings are for transistors....tubes have guidelines"
http://geek.scorpiorising.ca
  #8   Report Post  
robert casey
 
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Just be sure that you use "sharp cutoff pentodes". Some TV IF pentodes
were "remote cutoff". Variable gain depending on bias. Great way to do
AVC, but not good for audio work.



Hi Robert,

Why is that anyway?


These tubes have variable gm (or mu if triode), depending
on the DC bias on the control grid. Which means that
the output will not be linear. Not an issue if you are
using such a tube in an IF amplifier (signal level in
the millivolts, and most distortion products fall outside
the IF amp's passband). Bad for audio, which is a wide band
signal and higher levels. Excessive 2nd harmonic for sure.
If you have an audio amp using a 6AU6 try subbing a 6BA6.
It's sure to sound bad. A 6AU6 is a sharp cutoff pentode,
the 6BA6 is a remote cutoff pentode.
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