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Ian Iveson
 
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Default Calibrating tube tester - one question

200, 200, -4.6, 50 according to page 4 of

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

Page 7 of the same report shows curves for Vs = 200, so you can
check.

There are tonnes of sites with EL84 data, check via
http://www.duncanamps.com/

In general, you need to find the anode characteristic curves for
whatever screen voltage you are using. Choose the Va you will use,
and draw a vertical line on the curves at that voltage. It will
intersect with several curves. Find one intersection that gives a
convenient current: that gives you the required grid voltage. You
may need to interpolate between two intersections.

There are other presentations of the same data: grid and screen
characteristics, that can also be used...you just need one that
shows the relationship between Va, Vs, Vg and Ia. That's 4 variables
though so no single graph can express it all. That's why each set of
characteristics is a family of graphs, each with a family of curves.
Perhaps screen characteristics for Va=200V would be better for you.
Dunno if they are in that report, I don't have broadband.

cheers, Ian

"Richard J" wrote in message
...
Hi guys -

have got myself a tube tester that can do all sorts of tricks,

itīs a German
RPG70. It needs recalibration on the 50mA scale of the instrument.

Long
story, but getting there fast. Have documentation, but no

calibration
instructions.
Short question:

How much anode current will/does a new EL84 draw at the following

parameters
(stipulated by the RPG70 test card for EL84)?

Ua=200V, Ug2=60V, Ug=0V

An estimated guess would be somewhere in the region 17-20mA, but

knowing is
a lot better than guessing.

From the tube data sheet, I can guess that it would draw abt 48mA

at Ua=250,
UG2=250, Ug=0V. But: the tube data sheets all begin at 250V....and

not
200V - and my tube tester hasnīt got a 250V option. My math

doesnīt cover
this....

I have the following tester options:
Ua=25, 50,100,150,200V
Ug2=20,60,100,150,200V
Ug= negative 0-18V


Help, pse?

/Richard (used to simple emission testers, this is a different

ballgame)




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Richard J
 
Posts: n/a
Default

Ian,

thanks for the input. I found a chart that ties anode and G2 to the same
voltage, all the way down to 20V or so, and shows plate current with respect
to g1 voltage. From this chart, I can use the 50/50/0V, 100/100/0V points
without having to use the negative g1 voltage (which I donīt trust yet) in
order to get the 50mA and 100mA scales lined up reasonably well. WHen done,
I might just try the 200/200/-4,6 trick you sent me :-)

Cheers /Richard, tube tester wannabe


"Ian Iveson" wrote in message
...
200, 200, -4.6, 50 according to page 4 of

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

Page 7 of the same report shows curves for Vs = 200, so you can
check.

There are tonnes of sites with EL84 data, check via
http://www.duncanamps.com/

In general, you need to find the anode characteristic curves for
whatever screen voltage you are using. Choose the Va you will use,
and draw a vertical line on the curves at that voltage. It will
intersect with several curves. Find one intersection that gives a
convenient current: that gives you the required grid voltage. You
may need to interpolate between two intersections.

There are other presentations of the same data: grid and screen
characteristics, that can also be used...you just need one that
shows the relationship between Va, Vs, Vg and Ia. That's 4 variables
though so no single graph can express it all. That's why each set of
characteristics is a family of graphs, each with a family of curves.
Perhaps screen characteristics for Va=200V would be better for you.
Dunno if they are in that report, I don't have broadband.

cheers, Ian

"Richard J" wrote in message
...
Hi guys -

have got myself a tube tester that can do all sorts of tricks,

itīs a German
RPG70. It needs recalibration on the 50mA scale of the instrument.

Long
story, but getting there fast. Have documentation, but no

calibration
instructions.
Short question:

How much anode current will/does a new EL84 draw at the following

parameters
(stipulated by the RPG70 test card for EL84)?

Ua=200V, Ug2=60V, Ug=0V

An estimated guess would be somewhere in the region 17-20mA, but

knowing is
a lot better than guessing.

From the tube data sheet, I can guess that it would draw abt 48mA

at Ua=250,
UG2=250, Ug=0V. But: the tube data sheets all begin at 250V....and

not
200V - and my tube tester hasnīt got a 250V option. My math

doesnīt cover
this....

I have the following tester options:
Ua=25, 50,100,150,200V
Ug2=20,60,100,150,200V
Ug= negative 0-18V


Help, pse?

/Richard (used to simple emission testers, this is a different

ballgame)






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Richard J
 
Posts: n/a
Default

The simplest way to fix this was actually to just load the circuit with a
2K/10W resistor and 100V=50mA fullscale reading.
Turned out that one trimmer pot needed swapping.
After fixing this, all measurements suddenly made sense. Thanks!/

Richard


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