Trying to bring Keithly 600A Electrometer back to life

D

Don Taylor

Guest
I'd greatly appreciate any old memories that would help get an old
meter working again.

I picked up an old Keithly 600A electrometer up off Ebay, in good shape.
The batteries are long since dead, in fact, long since ceased
manufacture. But I got a bitmap scan of the manual off the Keithley
website.

B1 and B3 are RM42R 1.34 volt mercury cells, about D cell sized.

B2a B2b B6 and B7 are E146X 8.4 volt mercury cells, but someone has
already substituted recent vintage 9 volt cells in my instrument.

B4 and B5 are 413 30 volt dry cells, about the size of two 9 volt
cells stacked end to end.

Now the manual says that B1 drives the filaments of a pair of
balanced 5886 electrometer tubes.

I think I'm seeing that B3 drives the filaments of a pair of 6418's.

Now I'm thinking I can just chain 9 volt cells and a couple of AA
cells to substitute for each of the old 30 volt cells. From the
schematic they are driving the plate to +30 and the cathode to -30.
I am assuming that as long as the voltage is stable and I get close
to 30 volts on each of these I should be ok.

Since someone already did the substitution of 9 volt for 8.4 volt
mercury cells, if they haven't already toasted it I'm supposing
they thought this through and that it will work just fine with 9 v
cells.

What I'm most concerned about is swapping in 1.5 volt D cells for
the 1.34 volt mercury cells driving those filaments. That seems
like it might be pushing filaments harder and hotter than I would
be comfortable with, especially with the early stages of battery
life being above the labelled voltages. But RM42R cells are
non-existant now, as far as I have been able to find.

I've groped for any traces on the web of someone having done battery
swaps in 600A's and haven't found anything.

If anyone out there has a few brain cells that still remember
something about the 600A or updating it with current batteries I'd
really appreciate it. If I get it working I'd toss you pictures
of it making field mill measurements when I get it going.

many thanks
dont
(email address is valid, if that matters)
 
Don Taylor wrote:

I'd greatly appreciate any old memories that would help get an old
meter working again.

I picked up an old Keithly 600A electrometer up off Ebay, in good shape.
The batteries are long since dead, in fact, long since ceased
manufacture. But I got a bitmap scan of the manual off the Keithley
website.

B1 and B3 are RM42R 1.34 volt mercury cells, about D cell sized.

B2a B2b B6 and B7 are E146X 8.4 volt mercury cells, but someone has
already substituted recent vintage 9 volt cells in my instrument.

B4 and B5 are 413 30 volt dry cells, about the size of two 9 volt
cells stacked end to end.

Now the manual says that B1 drives the filaments of a pair of
balanced 5886 electrometer tubes.

I think I'm seeing that B3 drives the filaments of a pair of 6418's.

Now I'm thinking I can just chain 9 volt cells and a couple of AA
cells to substitute for each of the old 30 volt cells. From the
schematic they are driving the plate to +30 and the cathode to -30.
I am assuming that as long as the voltage is stable and I get close
to 30 volts on each of these I should be ok.

Since someone already did the substitution of 9 volt for 8.4 volt
mercury cells, if they haven't already toasted it I'm supposing
they thought this through and that it will work just fine with 9 v
cells.

What I'm most concerned about is swapping in 1.5 volt D cells for
the 1.34 volt mercury cells driving those filaments. That seems
like it might be pushing filaments harder and hotter than I would
be comfortable with, especially with the early stages of battery
life being above the labelled voltages. But RM42R cells are
non-existant now, as far as I have been able to find.

I've groped for any traces on the web of someone having done battery
swaps in 600A's and haven't found anything.

If anyone out there has a few brain cells that still remember
something about the 600A or updating it with current batteries I'd
really appreciate it. If I get it working I'd toss you pictures
of it making field mill measurements when I get it going.

many thanks
dont
(email address is valid, if that matters)
I have a number of tube manuals, and those two are not listed.
Click to expand...
I am guessing that the filament rating is 1.4V, like the 1R5, 1U4...
all-american 5 lineup.
"1.4V" means a nominal and is OK for 1.55V fresh dry cells.
In the manuals, i see a number of tubes with filament rateing of
1.25V and most are rectifiers.
I do not see a 1.25V filament rating for an electrometer tube, since
they were designed primarily for use with batteries; much more logical
to have a 1.4V rating for a standard dry cell.
Perhaps the mercury cells were used for longer useful life of the
instrument, and the lower voltage did not adversely affect the emmission
of the cathodes.
 
Don Taylor wrote:

I'd greatly appreciate any old memories that would help get an old
meter working again.

I picked up an old Keithly 600A electrometer up off Ebay, in good shape.
The batteries are long since dead, in fact, long since ceased
manufacture. But I got a bitmap scan of the manual off the Keithley
website.

B1 and B3 are RM42R 1.34 volt mercury cells, about D cell sized.

B2a B2b B6 and B7 are E146X 8.4 volt mercury cells, but someone has
already substituted recent vintage 9 volt cells in my instrument.

B4 and B5 are 413 30 volt dry cells, about the size of two 9 volt
cells stacked end to end.
Click to expand...

snip tale of battery hell

1.5v is only a 7% boost over 1.4v, and should be no problem for any
thermionic emitter.1.55v ditto. I used to boost CRTs 30% and never had
any problems.

If you were really determined to eek out every last second from dry
cells, you could always put a R on the batts to giev the 1.4v, but it
would achieve very little IRL.

But why not make a mains PSU to drive it all, instead of using stacks
of batteries?


NT
 
meow2222@care2.com wrote...
Don Taylor wrote:

I'd greatly appreciate any old memories that would help get an old
meter working again.

I picked up an old Keithly 600A electrometer up off Ebay, in good
shape. The batteries are long since dead, in fact, long since
ceased manufacture. But I got a bitmap scan of the manual off the
Keithley website.

snip tale of battery hell [ snip more battery hell ]

But why not make a mains PSU to drive it all, instead of using
stacks of batteries?
Click to expand...
Whatever he does, I recommend replacing the tube amplifier with a
nice NSC cmos low-bias-current opamp, like the LMC662 or LMC6001.
Free samples, http://www.national.com/pf/LM/LMC662.html
http://www.national.com/pf/LM/LMC6001.html



--
Thanks,
- Win
 
Robert Baer wrote:
Perhaps the mercury cells were used for longer useful life of the
instrument, and the lower voltage did not adversely affect the emmission
of the cathodes.
Click to expand...
Mercury cells were used because they had a very low internal resistance,
and because their cell voltage dropped practically not at all until they
were fully depleted. They thus were used anywhere an inexpensive,
accurate voltage reference was needed. This included power supplies
where changes in supply voltage would influence circuit operation.

Filament voltage would have influenced circuit operation (filaments,
are, after all inherently parameter corrupters :), but I don't remember
Hg cells used in any of the VTVM's I had to calibrate and repair in the
'60's and '70's, when they were still standard items.

John Perry
 
I work on that series. As stated above the mecury battery holds the
voltage longer at 1.4v
You need those steady voltages for these meters. There are circuits for
the 1.4v as they were used in cameras. Try google search such as
mercury battery subsitute or other variables. If you do serches on
mercury bateries you will find them in other countries but not US.
Doug
 
meow2222@care2.com wrote:

Don Taylor wrote:


I'd greatly appreciate any old memories that would help get an old
meter working again.

I picked up an old Keithly 600A electrometer up off Ebay, in good shape.
The batteries are long since dead, in fact, long since ceased
manufacture. But I got a bitmap scan of the manual off the Keithley
website.

B1 and B3 are RM42R 1.34 volt mercury cells, about D cell sized.

B2a B2b B6 and B7 are E146X 8.4 volt mercury cells, but someone has
already substituted recent vintage 9 volt cells in my instrument.

B4 and B5 are 413 30 volt dry cells, about the size of two 9 volt
cells stacked end to end.



snip tale of battery hell

1.5v is only a 7% boost over 1.4v, and should be no problem for any
thermionic emitter.1.55v ditto. I used to boost CRTs 30% and never had
any problems.

If you were really determined to eek out every last second from dry
cells, you could always put a R on the batts to giev the 1.4v, but it
would achieve very little IRL.

But why not make a mains PSU to drive it all, instead of using stacks
of batteries?


NT

One can introduce (erlatively speaking) a *LOT* of objectionable hum.
Click to expand...
 
Doug wrote...
I work on that series. As stated above the mecury battery holds the
voltage longer at 1.4v
You need those steady voltages for these meters. There are circuits
for the 1.4v as they were used in cameras. Try google search such as
mercury battery subsitute or other variables. If you do serches on
mercury bateries you will find them in other countries but not US.
Click to expand...
? Were you addressing my suggestion that Don replace the tube
amplifier with an NSC cmos opamp, like the LMC662 or LMC6001?
Were you pointing out that low-voltage parts (NSC's cmos opamps
run from as little as 4V) are well-suited to powering from a few
battery cells? The LMC6001 draws 450uA at 6V, and their slower
LMC6061 draws only 20uA (it's specs are slightly degraded). If
that's too much, Don can consider the micropower LMC6442, which
runs from lower voltages and takes even less current, only 2uA
at 2.2V, and is very well suited for 3 to 6V batteries.

Free samples are available for all these fempto-amp opamps,
http://www.national.com/pf/LM/LMC662.html
http://www.national.com/pf/LM/LMC6001.html
http://www.national.com/pf/LM/LMC6061.html
http://www.national.com/pf/LM/LMC6442.html Recommended.


--
Thanks,
- Win
 
Robert Baer wrote...
One can introduce (erlatively speaking) a *LOT* of
objectionable hum.
Click to expand...
Or not. My sub-pA HP instruments don't have hum problems,
and all my fempto-amp Keithley electrometers, including the
remote-head 642, run from the ac power line. It's a matter
of knowing how to make the transformer and power supply.


--
Thanks,
- Win
 
I was refering to keep the unit as is. The circuit uses a higher
voltage battery source and just regulated it.Keithly made battery
operated units and ac operated type. The AC operated still used the
1.4v mercury battery I believe for the ohms scale.
I'll have to search for notes at work.
dough
 
On Wed, 28 Dec 2005 21:21:14 -0600, Don Taylor wrote:

I'd greatly appreciate any old memories that would help get an old
meter working again.

I picked up an old Keithly 600A electrometer up off Ebay, in good shape.
The batteries are long since dead, in fact, long since ceased
manufacture. But I got a bitmap scan of the manual off the Keithley
website.

B1 and B3 are RM42R 1.34 volt mercury cells, about D cell sized.

B2a B2b B6 and B7 are E146X 8.4 volt mercury cells, but someone has
already substituted recent vintage 9 volt cells in my instrument.

B4 and B5 are 413 30 volt dry cells, about the size of two 9 volt
cells stacked end to end.

(Snip)

many thanks
dont
(email address is valid, if that matters)
Click to expand...
I don't have any suggestions on the 8.4 and 30 V batteries.

However, most rechargeable batteries have a nominal voltage
of about 1.2V. A pair of D cell rechargeable batteries should be
very close to the correct voltage.

In addition, the filaments probably draw a lot of current. Using
rechargeable batteries will keep your long term costs down.

The 8.4 and 30 V batteries probably provide bias voltages. The
current drain on them will be much less.

Aidan Grey
 
Winfield Hill wrote:

Robert Baer wrote...

One can introduce (erlatively speaking) a *LOT* of
objectionable hum.


Or not. My sub-pA HP instruments don't have hum problems,
and all my fempto-amp Keithley electrometers, including the
remote-head 642, run from the ac power line. It's a matter
of knowing how to make the transformer and power supply.


Yes; but the poster was going to use some undefinable PS to replace
Click to expand...
the batteries...
 
Robert Baer <robertbaer@earthlink.net> writes:
Winfield Hill wrote:
Robert Baer wrote...
One can introduce (erlatively speaking) a *LOT* of
objectionable hum.

Or not. My sub-pA HP instruments don't have hum problems,
and all my fempto-amp Keithley electrometers, including the
remote-head 642, run from the ac power line. It's a matter
of knowing how to make the transformer and power supply.

Yes; but the poster was going to use some undefinable PS to replace
the batteries...
Click to expand...
Actually I originally posted this. I was just hoping to find some
acceptable batteries, not trying to make this an exact replica of
what came from the factory 40+ years ago, but trying to keep most
of the original intent in place, get a cute old instrument running
again and still mostly meet the original specs without gutting it.

It was never my intent to debate the qualities of one model versus
another or whether it was possible to design lab quality ac supplies.
And it certainly wasn't saying that half a century of progress in
solid state devices couldn't produce as good or better an instrument.


Someone recommended looking at the web for pages describing substitues
for mercury cells in cameras that would have stable voltages. All
the results I found in that direction seemed to be replacing far
smaller batteries. The two 1.34 mercury cells in the 600A are about
D cell sized, these are heating the filaments of four (small) vaccuum
tubes for 500 hours. The ones I found on the web looked to be
button sized.

Some previous user of the 600A already substituted 9 volt cells for
the original 8 volt mercury cells and I presume, based on the
discussion, that these are also not going to have the stability
needed for repeatable measurements.

But I guess for the moment I'll try ordinary D and 9 volt cells to
generate all the voltages and see how bad it is.

Now if someone had a pointer to a description of building an
electrometer with current components I might try that, just to show
as a comparison.

I was groping for something really cute to have the 600A measure.
Now I think I've found it, the output of a little electric field mill.
If I can't find a plausibly priced old one I may have to build one.
 
Robert Baer wrote:
Winfield Hill wrote:
Robert Baer wrote...

One can introduce (erlatively speaking) a *LOT* of
objectionable hum.
Click to expand...
seems obvious enough that it would need to be designed to suit the app.


Or not. My sub-pA HP instruments don't have hum problems,
and all my fempto-amp Keithley electrometers, including the
remote-head 642, run from the ac power line. It's a matter
of knowing how to make the transformer and power supply.


Yes; but the poster was going to use some undefinable PS to replace
the batteries...
Click to expand...
Youre the first to mention an 'undefined' psu being used. I think its
fair to deduce that if someone is capable of restoring old meters, they
can define the requirements of the psu they need.


NT
 
Don Taylor wrote:

Robert Baer <robertbaer@earthlink.net> writes:

Winfield Hill wrote:

Robert Baer wrote...

One can introduce (erlatively speaking) a *LOT* of
objectionable hum.

Or not. My sub-pA HP instruments don't have hum problems,
and all my fempto-amp Keithley electrometers, including the
remote-head 642, run from the ac power line. It's a matter
of knowing how to make the transformer and power supply.

Yes; but the poster was going to use some undefinable PS to replace
the batteries...


Actually I originally posted this. I was just hoping to find some
acceptable batteries, not trying to make this an exact replica of
what came from the factory 40+ years ago, but trying to keep most
of the original intent in place, get a cute old instrument running
again and still mostly meet the original specs without gutting it.

It was never my intent to debate the qualities of one model versus
another or whether it was possible to design lab quality ac supplies.
And it certainly wasn't saying that half a century of progress in
solid state devices couldn't produce as good or better an instrument.


Someone recommended looking at the web for pages describing substitues
for mercury cells in cameras that would have stable voltages. All
the results I found in that direction seemed to be replacing far
smaller batteries. The two 1.34 mercury cells in the 600A are about
D cell sized, these are heating the filaments of four (small) vaccuum
tubes for 500 hours. The ones I found on the web looked to be
button sized.

Some previous user of the 600A already substituted 9 volt cells for
the original 8 volt mercury cells and I presume, based on the
discussion, that these are also not going to have the stability
needed for repeatable measurements.

But I guess for the moment I'll try ordinary D and 9 volt cells to
generate all the voltages and see how bad it is.

Now if someone had a pointer to a description of building an
electrometer with current components I might try that, just to show
as a comparison.

I was groping for something really cute to have the 600A measure.
Now I think I've found it, the output of a little electric field mill.
If I can't find a plausibly priced old one I may have to build one.
There are lithium 9V batteries with the same form factor as the
Click to expand...
"standard" 9V battery.
This would give an almost constant voltage during most of its life.
 
Don Taylor wrote:

Robert Baer <robertbaer@earthlink.net> writes:
Winfield Hill wrote:
Robert Baer wrote...
One can introduce (erlatively speaking) a *LOT* of
objectionable hum.

Or not. My sub-pA HP instruments don't have hum problems,
and all my fempto-amp Keithley electrometers, including the
remote-head 642, run from the ac power line. It's a matter
of knowing how to make the transformer and power supply.

Yes; but the poster was going to use some undefinable PS to replace
the batteries...

Actually I originally posted this. I was just hoping to find some
acceptable batteries, not trying to make this an exact replica of
what came from the factory 40+ years ago, but trying to keep most
of the original intent in place, get a cute old instrument running
again and still mostly meet the original specs without gutting it.

It was never my intent to debate the qualities of one model versus
another or whether it was possible to design lab quality ac supplies.
And it certainly wasn't saying that half a century of progress in
solid state devices couldn't produce as good or better an instrument.


Someone recommended looking at the web for pages describing substitues
for mercury cells in cameras that would have stable voltages. All
the results I found in that direction seemed to be replacing far
smaller batteries. The two 1.34 mercury cells in the 600A are about
D cell sized, these are heating the filaments of four (small) vaccuum
tubes for 500 hours. The ones I found on the web looked to be
button sized.

Some previous user of the 600A already substituted 9 volt cells for
the original 8 volt mercury cells and I presume, based on the
discussion, that these are also not going to have the stability
needed for repeatable measurements.

But I guess for the moment I'll try ordinary D and 9 volt cells to
generate all the voltages and see how bad it is.

Now if someone had a pointer to a description of building an
electrometer with current components I might try that, just to show
as a comparison.

I was groping for something really cute to have the 600A measure.
Now I think I've found it, the output of a little electric field mill.
If I can't find a plausibly priced old one I may have to build one.
Click to expand...
I find the whole idea kinda cool. also in my experience you can use any
recent "9V" battery in place of any 8.4V mercury battery in almost any
electronics. other batteries may pose different problems or advantages.
--
JosephKK
 
Don Taylor <dont@agora.rdrop.com> wrote in news:Rvqdnctdjf-HLSreRVn-
rQ@scnresearch.com:

Robert Baer <robertbaer@earthlink.net> writes:
Winfield Hill wrote:
Robert Baer wrote...
One can introduce (erlatively speaking) a *LOT* of
objectionable hum.

Or not. My sub-pA HP instruments don't have hum problems,
and all my fempto-amp Keithley electrometers, including the
remote-head 642, run from the ac power line. It's a matter
of knowing how to make the transformer and power supply.

Yes; but the poster was going to use some undefinable PS to replace
the batteries...

Actually I originally posted this. I was just hoping to find some
acceptable batteries, not trying to make this an exact replica of
what came from the factory 40+ years ago, but trying to keep most
of the original intent in place, get a cute old instrument running
again and still mostly meet the original specs without gutting it.

It was never my intent to debate the qualities of one model versus
another or whether it was possible to design lab quality ac supplies.
And it certainly wasn't saying that half a century of progress in
solid state devices couldn't produce as good or better an instrument.


Someone recommended looking at the web for pages describing substitues
for mercury cells in cameras that would have stable voltages. All
the results I found in that direction seemed to be replacing far
smaller batteries. The two 1.34 mercury cells in the 600A are about
D cell sized, these are heating the filaments of four (small) vaccuum
tubes for 500 hours. The ones I found on the web looked to be
button sized.

Some previous user of the 600A already substituted 9 volt cells for
the original 8 volt mercury cells and I presume, based on the
discussion, that these are also not going to have the stability
needed for repeatable measurements.

But I guess for the moment I'll try ordinary D and 9 volt cells to
generate all the voltages and see how bad it is.

Now if someone had a pointer to a description of building an
electrometer with current components I might try that, just to show
as a comparison.

I was groping for something really cute to have the 600A measure.
Now I think I've found it, the output of a little electric field mill.
If I can't find a plausibly priced old one I may have to build one.
Click to expand...
Maybe you could use a CR123 lithium cell (3V)and make a small regulator for
it,so it all fits in the space of the original mercury cell. For the 30 V
supplies,maybe 3 9V alkalines in series,that's probably a plate supply
anyways.Their physical size would be larger,though.

--
Jim Yanik
jyanik
at
kua.net
 
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