P
Phil Allison
Guest
Hi to all,
Picked up one of these 10MHz, single beam CROs from my local DSE store last
Tuesday - there were none on display and the staff seemed unaware of its
existence. The unit comes in a carry box, well packed with IEC mains lead,
10:1 probe and small handbook written by DSE staff.
Using a bench sine/ square generator and frequency counter when back at
home, I found my unit met published accuracy specs - time base speeds
being particularly accurate.
The *green* trace on the 75m dia tube face is particularly sharp and
geometry is very good all over the (external) graticule.
The vertical and horizontal positioning pots allow the pattern to be moved
right off the screen without visible limiting - so the deflection
amplifiers have adequate headroom.
The internal (Y) synch appears to function well as does the external and
LINE synch inputs. There is an X-Y mode that works fine too. There is no
"trace rotate " control, but two screws on the rear can be loosened to
allow the tube and hence trace to be lined up with the graticule OK.
Now for the insides:
-----------------------
With the vinyl coated steel sleeve slid off, there is a nice surprise.
This little CRO is *very* well made - reminiscent of the way Aussie firm
BWD built their famous CROs.
There are no SMD, all parts are "garden variety" - ie TO92 pack
transistors, TO220 regulators, a couple of fets and 3 bog standard ICs.
There is one large PCB for the PSU, deflection and synch circuits while a
smaller one at the front covers the vertical attenuator, input pre-amp and
time base circuitry.
Both sides of these (single sided, through hole) PCBs are fully accessible
for servicing !
A very neat, 20 VA, R-core transformer powers the CRO with a ferrite HF
inverter supplying 1200 volt DC to the tube. All internal voltages remain
regulated down to 200 volts AC input.
The 75mm tube is covered in a black, very snug fitting, full length
MAGNETIC SHIELD !! This is practically unheard of in a low cost CRO and
means the unit can be used, without annoying trace jitter, quite close to AC
power transformers used by other items on the bench or the equipment under
test.
The AC current draw was only 84mA rms ( 20 VA ) - so operation from a
small 12volt / 240 volt inverter supply is possible.
One anomaly I found - the CRO comes fitted with a 0.75 amp AC fuse. The
DSE handbook and the back label on the CRO both say this is the intended
value - which is nonsense since it offers no protection for the 20 VA
transformer. Best replace it with a 160 mA, slo-blo type.
Although not indicated anywhere, I expect the CRO was manufactured in China
or just possibly Korea. One would have to remove the CRO tube to see where
that was made.
My conclusion:
At a mere $ 128 inc GST and probe, this has got to be the biggest bargain in
*new* test gear you can buy in Australia.
........ Phil
Picked up one of these 10MHz, single beam CROs from my local DSE store last
Tuesday - there were none on display and the staff seemed unaware of its
existence. The unit comes in a carry box, well packed with IEC mains lead,
10:1 probe and small handbook written by DSE staff.
Using a bench sine/ square generator and frequency counter when back at
home, I found my unit met published accuracy specs - time base speeds
being particularly accurate.
The *green* trace on the 75m dia tube face is particularly sharp and
geometry is very good all over the (external) graticule.
The vertical and horizontal positioning pots allow the pattern to be moved
right off the screen without visible limiting - so the deflection
amplifiers have adequate headroom.
The internal (Y) synch appears to function well as does the external and
LINE synch inputs. There is an X-Y mode that works fine too. There is no
"trace rotate " control, but two screws on the rear can be loosened to
allow the tube and hence trace to be lined up with the graticule OK.
Now for the insides:
-----------------------
With the vinyl coated steel sleeve slid off, there is a nice surprise.
This little CRO is *very* well made - reminiscent of the way Aussie firm
BWD built their famous CROs.
There are no SMD, all parts are "garden variety" - ie TO92 pack
transistors, TO220 regulators, a couple of fets and 3 bog standard ICs.
There is one large PCB for the PSU, deflection and synch circuits while a
smaller one at the front covers the vertical attenuator, input pre-amp and
time base circuitry.
Both sides of these (single sided, through hole) PCBs are fully accessible
for servicing !
A very neat, 20 VA, R-core transformer powers the CRO with a ferrite HF
inverter supplying 1200 volt DC to the tube. All internal voltages remain
regulated down to 200 volts AC input.
The 75mm tube is covered in a black, very snug fitting, full length
MAGNETIC SHIELD !! This is practically unheard of in a low cost CRO and
means the unit can be used, without annoying trace jitter, quite close to AC
power transformers used by other items on the bench or the equipment under
test.
The AC current draw was only 84mA rms ( 20 VA ) - so operation from a
small 12volt / 240 volt inverter supply is possible.
One anomaly I found - the CRO comes fitted with a 0.75 amp AC fuse. The
DSE handbook and the back label on the CRO both say this is the intended
value - which is nonsense since it offers no protection for the 20 VA
transformer. Best replace it with a 160 mA, slo-blo type.
Although not indicated anywhere, I expect the CRO was manufactured in China
or just possibly Korea. One would have to remove the CRO tube to see where
that was made.
My conclusion:
At a mere $ 128 inc GST and probe, this has got to be the biggest bargain in
*new* test gear you can buy in Australia.
........ Phil
