"Ian Thompson-Bell" wrote in message
...
Doug Bannard wrote:
"Ian Thompson-Bell" wrote in message
...
I have being playing around with plate characteristics graphs, looking
at how basic parameters (gm,rp and mu) vary with operating point. The
most frustrating thing about this is that the published curves all
extend to rather large plate currents and voltages. For my preamp I am
working at plate currents of less than 5mA and the curves here are
rather cramped. Is there any source of curves that are expanded for the
lower plate current region?

Cheers

Ian

Hi Ian:

If you give me the range of plate currents and voltages, I can plot you a
set of curves on my tracer and email you a digital camera photo of same.
For example, if you tell me that the maximum y-axis current you want is
5mA and the x-axis voltage (Vak) is to be 300 volts, I can plot you a set
of 11 curves, including Vgk=0V. I can set the grid volts per step to
anything you'd like within reason.

Just let me know the values you want and I'll give it a try. Please also
let me know:

1) Do you want the screen grid connected through 100 ohms (or other
value) to the plate, or just a direct connection?
2) I can connect the suppressor grid anywhere you want. Either to the
plate or to cathode are the obvious choices. Where would you like it or
do you want curves for both connections?

All the best : Doug Bannard, P.Eng. )

Thanks Doug, that is a really kind offer. I am mainly interested in plate
currents up to 5mA and plate volts up to 250V. I am considering two
alternative triode connections of the 6AU6.

1. G3 and G2 tied to plate (no series resistors)
2. G3 and plate tied to ground with G2 used as a plate.

Curves for both configurations would be nice.

Many Thanks

Ian

Hi Ian:

I have run the curves and have sent scans of them in JPEG format to you
separately. To ensure that I am sending you meaningful scans, I have tested
two 6AU6s on my New London 901 Transconductance Analyzer, an instrument
which can test almost all receiving tubes under actual operating conditions,
with each element voltage regulated and adjustable.

One of the 6AU6s meets all of the requirements of a new tube as per the
standard pentode test conditions in the General Electric Tube Manual
(Essential Characteristics). These test conditions for pentode connection
are as follows:

For Vak = 250 volts, Vg2k = 150 volts, Cathode resistor of 68 ohms and G3
connected to cathode:

Ip (Ia) = 10.6 mA, Ig2 = 4.3 mA and gm = 5200 uS

The second 6AU6 has reached its end of life and under the same applied
voltages shows:

Ip(Ia) = 5mA, Ig2 = 1mA and gm = 2000 uS

I have sent you scans of each tube for grid steps of -0.5 volts /step
and -1.0 volts per step, for the standard triode connection (G2 and
G3 strapped to plate) and for the triode connection where G2 is used
as the anode with G3 and plate strapped to cathode. This gives you
8 scans in total.

I hope that these are of some help. Please feel free to share them with
anyone else if you wish.

All the best : Doug Bannard