Detectron Geiger Counter

[Chris F.]

I recently bought an old Detectron model DG-7 geiger counter. This is from
the early 50's and has three 1U5 tubes inside. Power requirements are 90
volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt bias
supply.
I went over the unit, replacing a selenium rectifier and testing the
tubes. The unit powers up, but generates a steady stream of pulses on it's
own, even with the probe detached. The frequency of the oscillation varies
with the range selector knob. The probe is working - when brought near a
source (a bunch of vaseline marbles) it will produce extra clicks in
addition to the stray ones generated by the unit.
I've checked all the other components - resistors, capacitors, etc. The
only thing I couldn't check is a very small tube, which looks like a
cold-cathode rectifier of some kind. I've also tried varying the B+ and bias
voltages. And I can't find a schematic, which makes matters worse.
I'm not sure what to do next. Any ideas?

 

[Sjouke Burry]

Chris F. wrote:

I recently bought an old Detectron model DG-7 geiger counter. This is from
the early 50's and has three 1U5 tubes inside. Power requirements are 90
volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt bias
supply.
I went over the unit, replacing a selenium rectifier and testing the
tubes. The unit powers up, but generates a steady stream of pulses on it's
own, even with the probe detached. The frequency of the oscillation varies
with the range selector knob. The probe is working - when brought near a
source (a bunch of vaseline marbles) it will produce extra clicks in
addition to the stray ones generated by the unit.
I've checked all the other components - resistors, capacitors, etc. The
only thing I couldn't check is a very small tube, which looks like a
cold-cathode rectifier of some kind. I've also tried varying the B+ and bias
voltages. And I can't find a schematic, which makes matters worse.
I'm not sure what to do next. Any ideas?


When the b+ becomes to high, the gas-discharge tubes start

oscillating, producing a steady stream of pulses.

So start with lowering b+ to zero, and then increase, until
either back at 90 volts, or the pulses re-appear.
At that point lower the voltage a bit, and re-check with your
radiation source.
Also there should be a capacitor across the tubes somewhere,
If so, check their quality(leakage and value).

 

[Jeff Liebermann]

On Thu, 22 Apr 2010 10:41:19 -0700, "Chris F." <zappyman@hotmail.com>
wrote:

I recently bought an old Detectron model DG-7 geiger counter.

Schematic of the DG-9 model:
<http://www.curtcass.com/detectron/dg9-sch.jpg>
Probably quite similar to the DG-7.

I went over the unit, replacing a selenium rectifier

Replace it with what? Is silicon, the B+ is probably too high.

At that age, 99.999999% of the electrolytic cazapitors have high ESR.
However, looking at the schematic, there are none. Weird.

and testing the tubes.

How? With a tube tester? I sometimes work on ancient Motorola radios
with pencil tubes. I have to make my own adapter to work in the tube
tester.

The unit powers up, but generates a steady stream of pulses on it's
own, even with the probe detached.

Ok, something is oscillating. I have some guesses based on the
schematic, but the right way is to get a scope, with a high voltage
probe (i.e. 100x) and sniff around for which section is oscillating.
My best guess is that since the beast doesn't have any power supply
filter capacitors on any of the batteries, and you've probably
assembled a mess of power supplies, batteries, and junk to simulate
the batteries, you have a fairly high impedance on the power supply
lines. Rather than fixing it with a proper battery, find a big fat
capacitor (with a suitable high voltage rating), and put it across the
power supply leads as close to the circuit (not as close to the
battery) as possible. The magic buzzword is "motorboating".

The frequency of the oscillation varies
with the range selector knob. The probe is working - when brought near a
source (a bunch of vaseline marbles) it will produce extra clicks in
addition to the stray ones generated by the unit.

Good, it's working.
<http://www.youtube.com/watch?v=U6x5mSp0PeA>
0.2mr/hr, about the same as background radiation. (I have the same
counter and the one in the video seems a bit insensitive).

I've checked all the other components - resistors, capacitors, etc. The
only thing I couldn't check is a very small tube, which looks like a
cold-cathode rectifier of some kind.

Nope. Probably a neon lamp used as a regulator. Photo?

I've also tried varying the B+ and bias
voltages. And I can't find a schematic, which makes matters worse.
I'm not sure what to do next. Any ideas?

Google for "Detectron Schematic".
<http://www.curtcass.com/detectron>
<http://www.curtcass.com/detectron/index2.html>

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS

 

[N_Cook]

Chris F. <zappyman@hotmail.com> wrote in message
news:4bd08a44$0$12419$9a566e8b@news.aliant.net...

I recently bought an old Detectron model DG-7 geiger counter. This is
from
the early 50's and has three 1U5 tubes inside. Power requirements are 90
volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt
bias
supply.
I went over the unit, replacing a selenium rectifier and testing the
tubes. The unit powers up, but generates a steady stream of pulses on it's
own, even with the probe detached. The frequency of the oscillation varies
with the range selector knob. The probe is working - when brought near a
source (a bunch of vaseline marbles) it will produce extra clicks in
addition to the stray ones generated by the unit.
I've checked all the other components - resistors, capacitors, etc. The
only thing I couldn't check is a very small tube, which looks like a
cold-cathode rectifier of some kind. I've also tried varying the B+ and
bias
voltages. And I can't find a schematic, which makes matters worse.
I'm not sure what to do next. Any ideas?

90V seems low for a GM, is there a step up circuit to 300V or so ?

 

[Chris F.]

Yes it uses some kind of step-up circuit, and the output to the GM tube is
about 300-400 volts.

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:hqrj97$20q$4@news.eternal-september.org...

Chris F. <zappyman@hotmail.com> wrote in message
news:4bd08a44$0$12419$9a566e8b@news.aliant.net...
I recently bought an old Detectron model DG-7 geiger counter. This is
from
the early 50's and has three 1U5 tubes inside. Power requirements are 90
volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt
bias
supply.
I went over the unit, replacing a selenium rectifier and testing the
tubes. The unit powers up, but generates a steady stream of pulses on
it's
own, even with the probe detached. The frequency of the oscillation
varies
with the range selector knob. The probe is working - when brought near a
source (a bunch of vaseline marbles) it will produce extra clicks in
addition to the stray ones generated by the unit.
I've checked all the other components - resistors, capacitors, etc. The
only thing I couldn't check is a very small tube, which looks like a
cold-cathode rectifier of some kind. I've also tried varying the B+ and
bias
voltages. And I can't find a schematic, which makes matters worse.
I'm not sure what to do next. Any ideas?




90V seems low for a GM, is there a step up circuit to 300V or so ?

 

[N_Cook]

Chris F. <zappyman@hotmail.com> wrote in message
news:4bd1b19c$0$12419$9a566e8b@news.aliant.net...

Yes it uses some kind of step-up circuit, and the output to the GM tube is
about 300-400 volts.

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:hqrj97$20q$4@news.eternal-september.org...
Chris F. <zappyman@hotmail.com> wrote in message
news:4bd08a44$0$12419$9a566e8b@news.aliant.net...
I recently bought an old Detectron model DG-7 geiger counter. This is
from
the early 50's and has three 1U5 tubes inside. Power requirements are
90
volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt
bias
supply.
I went over the unit, replacing a selenium rectifier and testing the
tubes. The unit powers up, but generates a steady stream of pulses on
it's
own, even with the probe detached. The frequency of the oscillation
varies
with the range selector knob. The probe is working - when brought near
a
source (a bunch of vaseline marbles) it will produce extra clicks in
addition to the stray ones generated by the unit.
I've checked all the other components - resistors, capacitors, etc.
The
only thing I couldn't check is a very small tube, which looks like a
cold-cathode rectifier of some kind. I've also tried varying the B+ and
bias
voltages. And I can't find a schematic, which makes matters worse.
I'm not sure what to do next. Any ideas?




90V seems low for a GM, is there a step up circuit to 300V or so ?

I use an ex military GM tube with ditched 1960s electronics (some strange
battery required although transistor) and my own inverter to sweep the
workshop every now and then . I forget what voltage drives it but I remember
that if it was set too high it would self discharge internally causing
regular clicks .
Now there is no thorium loaded gas mantles around these days , nor radium
dials , what is commonly around to give an above background check that they
are working ?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://diverse.4mg.com/index.htm

 

[GregS]

In article <hqsclg$d0v$1@news.eternal-september.org>, "N_Cook" <diverse@tcp.co.uk> wrote:

Chris F. <zappyman@hotmail.com> wrote in message
news:4bd1b19c$0$12419$9a566e8b@news.aliant.net...
Yes it uses some kind of step-up circuit, and the output to the GM tube is
about 300-400 volts.

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:hqrj97$20q$4@news.eternal-september.org...
Chris F. <zappyman@hotmail.com> wrote in message
news:4bd08a44$0$12419$9a566e8b@news.aliant.net...
I recently bought an old Detectron model DG-7 geiger counter. This is
from
the early 50's and has three 1U5 tubes inside. Power requirements are
90
volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt
bias
supply.
I went over the unit, replacing a selenium rectifier and testing the
tubes. The unit powers up, but generates a steady stream of pulses on
it's
own, even with the probe detached. The frequency of the oscillation
varies
with the range selector knob. The probe is working - when brought near
a
source (a bunch of vaseline marbles) it will produce extra clicks in
addition to the stray ones generated by the unit.
I've checked all the other components - resistors, capacitors, etc.
The
only thing I couldn't check is a very small tube, which looks like a
cold-cathode rectifier of some kind. I've also tried varying the B+ and
bias
voltages. And I can't find a schematic, which makes matters worse.
I'm not sure what to do next. Any ideas?




90V seems low for a GM, is there a step up circuit to 300V or so ?





I use an ex military GM tube with ditched 1960s electronics (some strange
battery required although transistor) and my own inverter to sweep the
workshop every now and then . I forget what voltage drives it but I remember
that if it was set too high it would self discharge internally causing
regular clicks .
Now there is no thorium loaded gas mantles around these days , nor radium
dials , what is commonly around to give an above background check that they
are working ?

If one has elevated radon levels, there is a rise near your furnace air filter,
if its electrostatic material. Still, you have to integrate the meter to see
average increases. I still have an old bedside clock around, as well
as my Pentax lens, 50mm vintage early 70's. You can buy Uranium stuff.
On one meter I use there is a calibration spot on the side. I don't know how many smoke detectors
have it, but it seems hard to measure through the case.

greg

 

[N_Cook]

GregS <zekfrivo@zekfrivolous.com> wrote in message
news:hqsd6m$mqd$1@usenet01.srv.cis.pitt.edu...

In article <hqsclg$d0v$1@news.eternal-september.org>, "N_Cook"
diverse@tcp.co.uk> wrote:
Chris F. <zappyman@hotmail.com> wrote in message
news:4bd1b19c$0$12419$9a566e8b@news.aliant.net...
Yes it uses some kind of step-up circuit, and the output to the GM tube
is
about 300-400 volts.

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:hqrj97$20q$4@news.eternal-september.org...
Chris F. <zappyman@hotmail.com> wrote in message
news:4bd08a44$0$12419$9a566e8b@news.aliant.net...
I recently bought an old Detectron model DG-7 geiger counter. This
is
from
the early 50's and has three 1U5 tubes inside. Power requirements
are
90
volts for the B+, two "D" cells for the tube filaments, and a 4.5
volt
bias
supply.
I went over the unit, replacing a selenium rectifier and testing
the
tubes. The unit powers up, but generates a steady stream of pulses
on
it's
own, even with the probe detached. The frequency of the oscillation
varies
with the range selector knob. The probe is working - when brought
near
a
source (a bunch of vaseline marbles) it will produce extra clicks in
addition to the stray ones generated by the unit.
I've checked all the other components - resistors, capacitors,
etc.
The
only thing I couldn't check is a very small tube, which looks like a
cold-cathode rectifier of some kind. I've also tried varying the B+
and
bias
voltages. And I can't find a schematic, which makes matters worse.
I'm not sure what to do next. Any ideas?




90V seems low for a GM, is there a step up circuit to 300V or so ?





I use an ex military GM tube with ditched 1960s electronics (some strange
battery required although transistor) and my own inverter to sweep the
workshop every now and then . I forget what voltage drives it but I
remember
that if it was set too high it would self discharge internally causing
regular clicks .
Now there is no thorium loaded gas mantles around these days , nor radium
dials , what is commonly around to give an above background check that
they
are working ?


If one has elevated radon levels, there is a rise near your furnace air
filter,
if its electrostatic material. Still, you have to integrate the meter to
see
average increases. I still have an old bedside clock around, as well
as my Pentax lens, 50mm vintage early 70's. You can buy Uranium stuff.
On one meter I use there is a calibration spot on the side. I don't know
how many smoke detectors
have it, but it seems hard to measure through the case.

greg

ordinary domestic smoke detectors use alpha emitters so not much use for GM
checking should anyone be unwise to break into the shielding (shielding
probably more to keep people out, than the alpha in, as almost anything
blocks it)

 

[Chris F.]

When the b+ becomes to high, the gas-discharge tubes start
oscillating, producing a steady stream of pulses.

So start with lowering b+ to zero, and then increase, until
either back at 90 volts, or the pulses re-appear.
At that point lower the voltage a bit, and re-check with your
radiation source.
Also there should be a capacitor across the tubes somewhere,
If so, check their quality(leakage and value).

Already tried that, and I replaced all the ceramic capacitors in the
circuit. By gas-discharge tube, are you referring to the neon lamp inside?
There's another tube, with just two leads, that I can't identify or test.
See this photo:
http://s282.photobucket.com/albums/kk275/packrat79/?action=view&current=detectron.jpg

 

[Chris F.]

Schematic of the DG-9 model:
http://www.curtcass.com/detectron/dg9-sch.jpg
Probably quite similar to the DG-7.

I came across that already, but it's quite different and therefore not much
help.

Replace it with what? Is silicon, the B+ is probably too high.

I tried putting a decade resistor in series with the diode, but even at

100k-ohms it still didn't make a difference. It still oscillates even with
the diode disconnected.

and testing the tubes.

How? With a tube tester? I sometimes work on ancient Motorola radios
with pencil tubes. I have to make my own adapter to work in the tube
tester.

Yes, I checked these with a tube tester, and even trying subbing them with
new-old-stock tubes.

Nope. Probably a neon lamp used as a regulator. Photo?

Here's a photo of the circuit:

http://s282.photobucket.com/albums/kk275/packrat79/?action=view&current=detectron.jpg

 

[Sjouke Burry]

Chris F. wrote:

When the b+ becomes to high, the gas-discharge tubes start
oscillating, producing a steady stream of pulses.

So start with lowering b+ to zero, and then increase, until
either back at 90 volts, or the pulses re-appear.
At that point lower the voltage a bit, and re-check with your
radiation source.
Also there should be a capacitor across the tubes somewhere,
If so, check their quality(leakage and value).

Already tried that, and I replaced all the ceramic capacitors in the
circuit. By gas-discharge tube, are you referring to the neon lamp inside?
There's another tube, with just two leads, that I can't identify or test.
See this photo:
http://s282.photobucket.com/albums/kk275/packrat79/?action=view&current=detectron.jpg


No, I was referring to a detector tube filled with neon, where

the voltage on the tube is just below the sustained ignition level,
and where the charged particle causes a conducting ion trail, which
discharges the parallel capacitor a little bit, causing the click
signal you can pick off. The feed resistor slowly restores the voltage
accross the tube/cap. The amplitude of the click shows the energy level
of the detected particle. Long ago I built a cosmic ray detector/display
using these tubes.
Name is geiger muller tube I think.

 

[Chris F.]

No, I was referring to a detector tube filled with neon, where
the voltage on the tube is just below the sustained ignition level,
and where the charged particle causes a conducting ion trail, which
discharges the parallel capacitor a little bit, causing the click signal
you can pick off. The feed resistor slowly restores the voltage
accross the tube/cap. The amplitude of the click shows the energy level
of the detected particle. Long ago I built a cosmic ray detector/display
using these tubes.
Name is geiger muller tube I think.

OK I understand. But that's still not the problem, because the unit produces
its own clicks whether the probe is connected or not........

 

[Jeff Liebermann]

On Fri, 23 Apr 2010 10:38:23 -0700, "Chris F." <zappyman@hotmail.com>
wrote:

Schematic of the DG-9 model:
http://www.curtcass.com/detectron/dg9-sch.jpg
Probably quite similar to the DG-7.

I came across that already, but it's quite different and therefore not much
help.

Oh, I was hoping they were similar. Sorry(tm).

Replace it with what? Is silicon, the B+ is probably too high.

I tried putting a decade resistor in series with the diode, but even at
100k-ohms it still didn't make a difference. It still oscillates even with
the diode disconnected.

I don't know exactly what series resistor is going to work. 100K is
certainly too large. When I was doing the same thing on much higher
power ancient Motorola radios, about 10 ohms 25 watts was about right.
I'll probably get yelled at for this suggestion, but use an ohmmeter
to mearsure the selenium recifiers forward resistance and use a
resistor with a slightly lower value. I dug around with Google and
found recommendations varying from 30 to 90 ohms for low power
devices.

<http://wiki.answers.com/Q/Can_you_replace_a_selenium_rectifier_with_a_silicon_rectifier>

Yes, I checked these with a tube tester, and even trying subbing them with
new-old-stock tubes.

The tubes are probably fine since it does go click on your vasalene
marbles.

Here's a photo of the circuit:
http://s282.photobucket.com/albums/kk275/packrat79/?action=view&current=detectron.jpg

Yech. Note the big paper electrolytic cazapitor. I can't tell if
it's a power supply filter cap or across the meter to smooth the
output. If across the power supply, replace it as judging by the age
and type, it's almost certainly dead. If you have an ESR tester, use
it. (If you don't have one, buy or build one).

I'll stand on my comments that your clip lead and external power
supply kludge is probably causing problems. Find some suitable
electrolytics and place them across where the battery would normally
connect. The idea is to reduce the impedance that the counter sees in
the direction of the power supplies. That should reduce the
motorboating (oscillation).


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS

 

[N_Cook]

Jeff Liebermann <jeffl@cruzio.com> wrote in message
news:kcf4t5hlkdkjj4h04vns4qf7t8d3dhcsob@4ax.com...

On Fri, 23 Apr 2010 10:38:23 -0700, "Chris F." <zappyman@hotmail.com
wrote:

Schematic of the DG-9 model:
http://www.curtcass.com/detectron/dg9-sch.jpg
Probably quite similar to the DG-7.

I'll stand on my comments that your clip lead and external power
supply kludge is probably causing problems. Find some suitable
electrolytics and place them across where the battery would normally
connect. The idea is to reduce the impedance that the counter sees in
the direction of the power supplies. That should reduce the
motorboating (oscillation).


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS

Does USA "kludge" = UK "bodge" ?

 

[PeterD]

On Sat, 24 Apr 2010 09:02:32 +0100, "N_Cook" <diverse@tcp.co.uk>
wrote:

Jeff Liebermann <jeffl@cruzio.com> wrote in message
news:kcf4t5hlkdkjj4h04vns4qf7t8d3dhcsob@4ax.com...
On Fri, 23 Apr 2010 10:38:23 -0700, "Chris F." <zappyman@hotmail.com
wrote:

Schematic of the DG-9 model:
http://www.curtcass.com/detectron/dg9-sch.jpg
Probably quite similar to the DG-7.

I'll stand on my comments that your clip lead and external power
supply kludge is probably causing problems. Find some suitable
electrolytics and place them across where the battery would normally
connect. The idea is to reduce the impedance that the counter sees in
the direction of the power supplies. That should reduce the
motorboating (oscillation).


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS


Does USA "kludge" = UK "bodge" ?

Yes...

 

[Chris F.]

I'll stand on my comments that your clip lead and external power
supply kludge is probably causing problems. Find some suitable
electrolytics and place them across where the battery would normally
connect. The idea is to reduce the impedance that the counter sees in
the direction of the power supplies. That should reduce the
motorboating (oscillation).

I tried putting a 100uF cap in that area, the result was that it greatly
increased the frequency of the stray clicks....
I wonder if a row of 10 9-volt batteries would work?

 

[Jeff Liebermann]

On Sat, 24 Apr 2010 07:51:13 -0700, "Chris F." <zappyman@hotmail.com>
wrote:

I'll stand on my comments that your clip lead and external power
supply kludge is probably causing problems. Find some suitable
electrolytics and place them across where the battery would normally
connect. The idea is to reduce the impedance that the counter sees in
the direction of the power supplies. That should reduce the
motorboating (oscillation).

I tried putting a 100uF cap in that area, the result was that it greatly
increased the frequency of the stray clicks....

Did you figure out where the yellow electrolytic in the photo was
connected? Power supply filter or meter integrator?

Find an oscilloscope that can tolerate some high voltage (i.e. 100x
probe). Look at the power supply line. Got pulses? If so, get rid
of them with a filter cap.

Old carbon composition resistors tend to change value with age (and
moisture). With the power off, you might walk though the pile and see
if there are any that are radically off value. I don't think this is
causing the problem, but it might be contributory.

I wonder if a row of 10 9-volt batteries would work?

Probably, but rather expensive. It should work with your external
power supplies, but due to the apparent lack of power supply
filtering, it might be oscillating.

If all else fails, trace out the schematic. It doesn't look all that
messy and you can probably use the DG-9 schematic as a guide. The
author of the web site where we found the DG-9 schematic is the
founders son. Send him email asking if he has a DG-7 schematic or if
he knowns anyone that can help.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Sat, 24 Apr 2010 09:02:32 +0100, "N_Cook" <diverse@tcp.co.uk>
wrote:

Does USA "kludge" = UK "bodge" ?

I think so. Also sometimes spelled kluge.
<http://en.wikipedia.org/wiki/Kludge>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Chris F.]

Did you figure out where the yellow electrolytic in the photo was
connected? Power supply filter or meter integrator?

It's connected across the meter.

Find an oscilloscope that can tolerate some high voltage (i.e. 100x
probe). Look at the power supply line. Got pulses? If so, get rid
of them with a filter cap.

Already tried that.... or are you talking about the AC line feeding my
transformer/rectifier/cap power supply?

Old carbon composition resistors tend to change value with age (and
moisture). With the power off, you might walk though the pile and see
if there are any that are radically off value. I don't think this is
causing the problem, but it might be contributory.

Checked them all, and all are well within their specified tolerances.

I wonder if a row of 10 9-volt batteries would work?

Probably, but rather expensive. It should work with your external
power supplies, but due to the apparent lack of power supply
filtering, it might be oscillating.

If all else fails, trace out the schematic. It doesn't look all that
messy and you can probably use the DG-9 schematic as a guide. The
author of the web site where we found the DG-9 schematic is the
founders son. Send him email asking if he has a DG-7 schematic or if
he knowns anyone that can help.

I might do that. Can't think of anything else it might be, as it's really a

rather basic circuit. BTW that small tube with the 2 leads I mentioned is a
5841 (voltage regulator), and I don't have a sub for it.

 

[tm]

"Chris F." <zappyman@hotmail.com> wrote in message
news:4bd32e4e$0$12423$9a566e8b@news.aliant.net...

If all else fails, trace out the schematic. It doesn't look all that
messy and you can probably use the DG-9 schematic as a guide. The
author of the web site where we found the DG-9 schematic is the
founders son. Send him email asking if he has a DG-7 schematic or if
he knowns anyone that can help.

I might do that. Can't think of anything else it might be, as it's really
a rather basic circuit. BTW that small tube with the 2 leads I mentioned
is a 5841 (voltage regulator), and I don't have a sub for it.

Check this out:

http://www.dvq.com/geiger/heath_rc1.pdf

Googleing says it is a 900 volt regulator. maybe a stack of 150 volt zeners
would work.

I did see some replacements available.