[[email protected]]

I'm having trouble understanding how to implement this in a test. The items
(Eb + Ec2 = 240)appear on a set of plate voltage curves for plate current
vs. control grid . Does this mean that the plate and the screen voltage are
the same value per curve, the plate voltage and the screen voltage are added
together per each curve, or the screen voltage is held constant at 240 volts
while the plate voltages are changed for each curve? I'm trying to set this
up in a test and I'm not sure what to do this parameter. Thanks for any
help.
D.E.

[Patrick Turner]

wrote:

I'm having trouble understanding how to implement this in a test. The items
(Eb + Ec2 = 240)appear on a set of plate voltage curves for plate current
vs. control grid . Does this mean that the plate and the screen voltage are
the same value per curve, the plate voltage and the screen voltage are added
together per each curve, or the screen voltage is held constant at 240 volts
while the plate voltages are changed for each curve? I'm trying to set this
up in a test and I'm not sure what to do this parameter. Thanks for any
help.
D.E.

Eb and Ec2 are somewhat misleading.

But Eb came from the old idea of a battery supply, and don't ask me
where Ec2
came from when it means screen voltage. Should be Ea and Eg2, where
E means electric voltage potential and a means anode and g means grid,
and 2 means the second grid
or screen. Tubes can have many grids.

Voltages Ea and Eg2 are always assumed to be from anode to cathode or
screen to cathode,
regardless of cathode or grid ( g1) biasing methods.

Probably the data you have in front of you does mean Ea and Eg2 are the
same voltage.

One can hold the tubes anode AND screen voltage constant, and alter
only the grid 1 voltage, and record the current change, thus be able to
plot
the curve for transconductance, ie, current change per volt of grid
change.

Or you can plot the normal set of "plate curves"
to get Ea, horizontal, versus Ia, vertical, for varying fixed values of
grid 1 voltage
while also keeping Eg2 at a fixed voltage.

This shows the pentode anode curves for dynamic anode resistance, Ra,
for varying g1 voltages.

Then you get another different set of Ea/Ia curves for the anode
if the screen is connected to it for triode connection,
and you vary the anode voltage and record current
for fixed values of grid voltage.

The Eb or Ec2 ( ie Ea&Eg2 ) are not summed in data sheets afaik.

To test a tube yourself, you need to have a low impedance variable
ac supply which can be biased from a low impedance dc supply between
100Vdc and 1,000V
depending on what you are testing. The V swing from the AC should be +/-
the dc supply voltage.
So a secondary of a mains tranny could be used, with variable taps.
And one end of the secondary is taken to a low impedance dc supply.

Use 10 ohms in series with the anode to record dc and ac current.
Have a low impedance negative variable grid voltage.

Beware to never force the tube into anode or screen dissipation higher
than maximums
allowable or higher than average. So rehearse the testing before doing
one,
then measure quickly and reliably.

Maybe you should read more about all this in RDH4.

[[email protected]]

Thankks so much Patrick for the reply. After I viewed your reply I found
another set of data sheets for the tube (6EJ7). On the curves the data was
the same except that Va=Vg2=240 volts. Seeing this along with your post
pretty well setteled it for me.
Thanks again,
Don

[Ian Iveson]

Don wrote:

Thankks so much Patrick for the reply. After I viewed
your reply I found
another set of data sheets for the tube (6EJ7). On the
curves the data was
the same except that Va=Vg2=240 volts. Seeing this along
with your post
pretty well setteled it for me.

I was wondering how you could get a "set of plate voltage
curves" if the anode voltage is fixed at 240V. Then I
wondered how "for plate current v control grid." fitted in
to the picture.

So I looked at a data sheet. Just so everyone can see what
you mean, here it is, for a "close or identical" EF184

http://tdsl.duncanamps.com/pdf/ef184.pdf

Page 3 shows an example of the curves you mean. What should
we call such a set of curves? "Grid characteristics" springs
to mind but I may well be wrong. Not to be confused with
"Anode characteristics" which would, for me, show anode
current v anode voltage, with a set of curves, each for a
different value of Vg1. For triode connection they look
quite similar.

Anyway, "set of plate voltage curves" isn't a good name,
because in your example each curve shows anode current v
control grid voltage.

Note that your label "Va=Vg2=240 volts" (in my link 230) is
a label for one curve only. For the next curve, the label
"200" means "Va=Vg2=200 volts".

If it were a label for the whole graph, it would be written
somewhere else, or in a box as with "Vg3=0V"

Ian

[[email protected]]

Thanks Pat, this really helped. I'm not sure what RDH4 is. Can you explain
this a littlt bit?.

Thanks again,
Don

[[email protected]]

Thanks Ian. What you explained is exactly correct. The plate and screen
voltages change with every curve. I started testing these tubes with this
configuration (plate and screen connected together), changing the grid
voltage (-2 to -3 vdc) and writing down the plate voltage and plate current
at these points. My supply voltage is set to 350 vdc, Rl is 15k, and heater
is 6.3 vdc. According to my load line I should be seeing a current swing of
about 8.7 ma to 11.9 ma. My plate current readings tend to be high. I'm
getting 10 ma to 18 ma swing. Some of the tubes are testing right on.
Would you discribe the tubes with the higher current as being leaky or bad?

Thanks again,
Don
P.S. I found RDH4

[[email protected]]

Ok, Ifound RDH4
Thanks so much,
Don

[David R Brooks]

Patrick Turner wrote:

wrote:
I'm having trouble understanding how to implement this in a test. The items
(Eb + Ec2 = 240)appear on a set of plate voltage curves for plate current
vs. control grid . Does this mean that the plate and the screen voltage are
the same value per curve, the plate voltage and the screen voltage are added
together per each curve, or the screen voltage is held constant at 240 volts
while the plate voltages are changed for each curve? I'm trying to set this
up in a test and I'm not sure what to do this parameter. Thanks for any
help.
D.E.

Eb and Ec2 are somewhat misleading.

But Eb came from the old idea of a battery supply, and don't ask me
where Ec2
came from when it means screen voltage. Should be Ea and Eg2, where
E means electric voltage potential and a means anode and g means grid,
and 2 means the second grid
or screen. Tubes can have many grids.

[snip]
I think the terminology relates to the (very) old US usage, of A
(heater), B (HT) and C (bias) batteries, back in the 1920's or so.
Given that, Eb is the HT (anode), and Ec2 is the second (g2 or screen)
grid supply.

[Patrick Turner]

wrote:

Thanks Pat, this really helped. I'm not sure what RDH4 is. Can you explain
this a littlt bit?.

Thanks again,
Don

RDH4 is the Radiotron Designer's Handbook, 4th Ed, 1955 by Fritz
Langford-Smith ( and a team of other good men )

Its online some where and can be downloaded.

I prefer a paper copy because its easier to read at the kitchen table or
in bed.

There are a number of other hard backed books used by electronics
engineering students
in the 1950s, but many are being hoarded by speculative bookhoarders
so only a tiny amount of second hand old electronics books are seen in
books stores now
which get collections from deceased estate auctions, and flog them off
on ebay asap
or they go broke.

As my old granpa said,

"If yer don't look, yer won't know."

Patrick Turner.

[Patrick Turner]

David R Brooks wrote:

Patrick Turner wrote:

wrote:
I'm having trouble understanding how to implement this in a test. The items
(Eb + Ec2 = 240)appear on a set of plate voltage curves for plate current
vs. control grid . Does this mean that the plate and the screen voltage are
the same value per curve, the plate voltage and the screen voltage are added
together per each curve, or the screen voltage is held constant at 240 volts
while the plate voltages are changed for each curve? I'm trying to set this
up in a test and I'm not sure what to do this parameter. Thanks for any
help.
D.E.

Eb and Ec2 are somewhat misleading.

But Eb came from the old idea of a battery supply, and don't ask me
where Ec2
came from when it means screen voltage. Should be Ea and Eg2, where
E means electric voltage potential and a means anode and g means grid,
and 2 means the second grid
or screen. Tubes can have many grids.

[snip]
I think the terminology relates to the (very) old US usage, of A
(heater), B (HT) and C (bias) batteries, back in the 1920's or so.
Given that, Eb is the HT (anode), and Ec2 is the second (g2 or screen)
grid supply.

Probably right.

I like Ea, Eg2, Eg1, because it references all Electric potentials, ie,
Vdc
in reference to the cathode Ek taken as 0V.


Va, Vg2, Vg1 Vk are ac signal voltages as the electrodes, usually
referenced to the 0V amp rail unless otherwise spelled out.

B+ usually always means the Vdc at the OPT CT or at any other place
downstream in an RCRCRC
type filter chain to the input stage and the points where a load is
connected to a Vdc
with low Zac, and Vdc is referenced to 0V.

B- usually means the negative grid bias supply but could be a negative
rail
like the B+.

The context always should be clearly spelled out in discussions because
all too often
guys don't, and lots of BS and confusion follows.

Patrick Turner.