Isco rocks! I just got some documentation from the company, and I'm sharing for the rest of y'all who have one too.
http://www.eisenhower.org/eric/isco/494.pdf
Operations
Theory
Schematics
Layout
Troubleshooting
Tips on replacement parts, w/ Newark numbers!
Enjoy!
http://www.eisenhower.org/eric/isco/494.pdf
Operations
Theory
Schematics
Layout
Troubleshooting
Tips on replacement parts, w/ Newark numbers!
Enjoy!
Yes, kudos to Isco. They guy said it was "refreshing" to find someone who knew what vacuum tubes are, and was happy to help.
They are fairly cheap here. I know a guy with a pile of them. Probably get it for ~$50, but it will cost $85 to ship it across the pond. Then you have to convert it to 220/240, but that is documented in the .pdf
They are fairly cheap here. I know a guy with a pile of them. Probably get it for ~$50, but it will cost $85 to ship it across the pond. Then you have to convert it to 220/240, but that is documented in the .pdf
I have a Bio-Rad and a Dan-Kar electrophoresis supply, both recently acquired. I was thinking of latching on to one of the Isco 494s, but I couldn't get enough information in a short time to make an informed choice. I instead got a Bio-Rad 500/200 and a Dan-Kar DR203. The Bio-Rad unit is 500V/200A, as its model number suggests, and the Dan-Kar can go up to 2kV/200mA. The Bio-Rad supply has some intelligent things going on, as it has semis on heat sinks and a cooling fan. I suspect the Dan-Kar is a rough and ready Variac controlled power supply with nominal filtering. I'll know more when I pop their respective hoods. Both are good enough to allow me to hack around with tubes more easily, though they lack the sophisticated features offered on the Isco supply. A tip of the hat to the gentleman on this list who first suggested using electrophoresis supplies for vacuum tube circuit development....
The 493 is up to 1kV. 400ma @ 600V, 200ma @ 1kv. Should also be a fine bench ps.
Here is the schematic. Isco is digging around for the manual.
http://www.eisenhower.org/eric/isco/493sch.pdf
BTW, did anyone else see the Fluke 407 go for $350 on Ebay? Scary.
Here is the schematic. Isco is digging around for the manual.
http://www.eisenhower.org/eric/isco/493sch.pdf
BTW, did anyone else see the Fluke 407 go for $350 on Ebay? Scary.
Well, I got 29 pages of 493 manuals, as separate tif files. Here's is all the Isco docs I got:
http://www.eisenhower.org/eric/isco/
I should correct my prior post in that the 493 will 400ma at 500v, not 600v.
Hope this is helpful to somebody.
http://www.eisenhower.org/eric/isco/
I should correct my prior post in that the 493 will 400ma at 500v, not 600v.
Hope this is helpful to somebody.
ISCO 494 modification for 1200V@150mA max (not 90)
Hello, I am trying to modify the ISCO 494 that has an output of 2000V @ 90mA if all controls are set to max. My target is to get 1200 Volts @ 150 mA (this is the same power). You understand the use of it, it can feed 2 SE channels with GM70, 845, 211 etc. Or 1 Push Pull channel with them.
So by checking the circuit I see that 2kV's come out by the following circuit: The 250 Vac secondary is multiplied twice, by 2 separate triplers. Those triplers that give 1 KV and -1 KV referenced to their common are added so the final output is 2 KV. If 2 electrolytics are removed (good as spares!) and a couple of jumpers bypass their respective diodes, this thing becomes a dual doubler/adder that finally gives approx 1300 Volts. I will come back to write the exact parts to be removed, using their numbering as seen on the pcb.
So far so good, the ISCO became a power supply that can't go over 1.3 KV. Have in mind that if something fails in the regulation circuitry (as mentioned in the manual) the output can become 2KV full power, no matter if during tests someone is using it at say 1 KV.
So this easy mod at the worst case will make the unit not to exceed 1.3 KV.
What needs to be done next is to make all feedback circuitry keep working as before, and get the double mA's.
It must become adjustable from 0-1200 V, with current limiting from some mA's up to 150mA (or slightly more, why not?) . This is the part that I am working now, still no positive results, as for the moment the controls fail to work. I welcome any suggestions.
Hello, I am trying to modify the ISCO 494 that has an output of 2000V @ 90mA if all controls are set to max. My target is to get 1200 Volts @ 150 mA (this is the same power). You understand the use of it, it can feed 2 SE channels with GM70, 845, 211 etc. Or 1 Push Pull channel with them.
So by checking the circuit I see that 2kV's come out by the following circuit: The 250 Vac secondary is multiplied twice, by 2 separate triplers. Those triplers that give 1 KV and -1 KV referenced to their common are added so the final output is 2 KV. If 2 electrolytics are removed (good as spares!) and a couple of jumpers bypass their respective diodes, this thing becomes a dual doubler/adder that finally gives approx 1300 Volts. I will come back to write the exact parts to be removed, using their numbering as seen on the pcb.
So far so good, the ISCO became a power supply that can't go over 1.3 KV. Have in mind that if something fails in the regulation circuitry (as mentioned in the manual) the output can become 2KV full power, no matter if during tests someone is using it at say 1 KV.
So this easy mod at the worst case will make the unit not to exceed 1.3 KV.
What needs to be done next is to make all feedback circuitry keep working as before, and get the double mA's.
It must become adjustable from 0-1200 V, with current limiting from some mA's up to 150mA (or slightly more, why not?) . This is the part that I am working now, still no positive results, as for the moment the controls fail to work. I welcome any suggestions.
ISCO 494 MODIFICATION DONE, max 1200v @ 300mA !!!
It took me some time to do this mod due to other projects but now it is done and working! The 494 that had a max voltage of 2kv @ 90 mA now has been modified and gives 0-1200V @ 300mA. If something fails, uncontrolled voltage will not exceed 1300V under no load. It can also work at limited current settings as the 600V current control knob is still functioning.
Another mod in progress is to silence the humming transformer, almost done.
Anyone interested in the mod procedure can ask me for detailed instructions.
It took me some time to do this mod due to other projects but now it is done and working! The 494 that had a max voltage of 2kv @ 90 mA now has been modified and gives 0-1200V @ 300mA. If something fails, uncontrolled voltage will not exceed 1300V under no load. It can also work at limited current settings as the 600V current control knob is still functioning.
Another mod in progress is to silence the humming transformer, almost done.
Anyone interested in the mod procedure can ask me for detailed instructions.
I have one of these supplies and would be interested in the details as I am now building a pair of GM70 based SE amps and the higher current capability would allow me to run a pair at their target B+ while I work on the PSU design..
Hello Kevin,
I am preparing the mod's text, as for the moment is handwritten.
Homemade potting of the transformer is done, I will reconnect it probably tomorrow to hear the result of silencing.
I intend to use this ps for powering a Music Angel 845 SE that has been modified to become a GM70 SE, so it has to be quiet mechanically.
My next project is a GM70 Push Pull class A stereo amp. So it must be able to deliver a total of 4x70mA at 1200Volts. For the moment it does, on my dummy load. This is something you need to construct, as it will help during the adjustments. Just connect the biggest resistors you have (50-200W) to make approximately 3900 Ohms, and secure them on a metal plate to avoid setting a fire on the bench. Teflon cables will help. It appears that this ps can deliver far more power than 2000V x 90mA, so the dummy dissipates 1200V x 295 mA whithout any overheated components inside. So I will soon be back with the detailed instructions.
I am preparing the mod's text, as for the moment is handwritten.
Homemade potting of the transformer is done, I will reconnect it probably tomorrow to hear the result of silencing.
I intend to use this ps for powering a Music Angel 845 SE that has been modified to become a GM70 SE, so it has to be quiet mechanically.
My next project is a GM70 Push Pull class A stereo amp. So it must be able to deliver a total of 4x70mA at 1200Volts. For the moment it does, on my dummy load. This is something you need to construct, as it will help during the adjustments. Just connect the biggest resistors you have (50-200W) to make approximately 3900 Ohms, and secure them on a metal plate to avoid setting a fire on the bench. Teflon cables will help. It appears that this ps can deliver far more power than 2000V x 90mA, so the dummy dissipates 1200V x 295 mA whithout any overheated components inside. So I will soon be back with the detailed instructions.
ISCO 494 ELECTROPHORESIS modification procedure by adam2a3 (SV1CDU)
Original spec of 0-2000V @ 90mA will become 0-1250V @ 290mA max.
1.Remove C25, C26, C28, C23 (a pair of terminal lugs carrying 47K resistors will be removed too)
2. On the pcb, solder a piece of wire between terminals of C28.
Same between terminals of C23
3. Cut/remove diodes CR30, CR31, CR39, CR31 and SHORT CR37 and CR35
4. Cut the following cables at a distance of 1 inch from the pcb
CUT: 29 blue, 33 yel, 28 red, 36 grey, 37 purple
5. Connect 36 grey to 37 purple (the 1 inch parts, coming out from pcb)
6. Connect 29 blue to 33 yellow (the 1 inch parts, coming out from pcb)
7. Insulate all exposed cable ends using heatshrink tubing (8 places in total)
8. Short R66=66 Ohm 11W by soldering a small wire underneath. You may remove this resistor or just leave it in place..
9. Similarly for R59
10.Replace R150=469K by a 820K 0.5W
11. Unsolder one side of R154=66K , Connect a 12 K 1/4W to the lifted lead and it’s other end to the pcb. Now R154 will become (66+12) K
12. Remove R62 and R63 (both 47K 11W).
13. RECHECK EVERYTHING
14.Connect a DVM having a max 1000Vdc scale to the HV black/white terminals
14.Adjust watts and current knobs to 100%, voltage to zero. Power on.
15. Turn up the voltage knob to 800V as read on the ISCO panel meter.
16. If the dvm shows a different voltage, adjust R100 until dvm reads 800V.
17. Power off, remove dvm, connect the dummy load at the hv terminals, (mine is 3980 Ohms @ 200W), set Voltage knob close to zero, turn the center knob to 600V 300mA, and power on again.
18. Set Voltage knob to 100%. Adjust R149 for 1250V at the panel meter, and V light just coming on.
19. Set Current knob to 100%. Adjust R153 until a current of almost 300mA is observed on the right panel meter and mA light just comes on.
20. Multiply V and mA and after turning selector to Watts, check reading on left panel meter. Adjust if needed R164 until correct power is shown.
By the above mod, the positive and negative triplers become doublers so max voltage is reduced. At the same time more mA’s become available. All current values shown on the limiter knob in 2 scales (600 and 2000V) now are still valid except that voltage is always 0-1250V. So by setting it at 600V 300mA we get 0-1250V 290mA. Before this mode you may measure voltages accros big electrolytics while unit is set to 2KV. Those caps that have low voltages usually are the leaky ones, so can be removed. 4 caps will be removed and become spares after the mode, allowing for swaps.
Good Luck!
Original spec of 0-2000V @ 90mA will become 0-1250V @ 290mA max.
1.Remove C25, C26, C28, C23 (a pair of terminal lugs carrying 47K resistors will be removed too)
2. On the pcb, solder a piece of wire between terminals of C28.
Same between terminals of C23
3. Cut/remove diodes CR30, CR31, CR39, CR31 and SHORT CR37 and CR35
4. Cut the following cables at a distance of 1 inch from the pcb
CUT: 29 blue, 33 yel, 28 red, 36 grey, 37 purple
5. Connect 36 grey to 37 purple (the 1 inch parts, coming out from pcb)
6. Connect 29 blue to 33 yellow (the 1 inch parts, coming out from pcb)
7. Insulate all exposed cable ends using heatshrink tubing (8 places in total)
8. Short R66=66 Ohm 11W by soldering a small wire underneath. You may remove this resistor or just leave it in place..
9. Similarly for R59
10.Replace R150=469K by a 820K 0.5W
11. Unsolder one side of R154=66K , Connect a 12 K 1/4W to the lifted lead and it’s other end to the pcb. Now R154 will become (66+12) K
12. Remove R62 and R63 (both 47K 11W).
13. RECHECK EVERYTHING
14.Connect a DVM having a max 1000Vdc scale to the HV black/white terminals
14.Adjust watts and current knobs to 100%, voltage to zero. Power on.
15. Turn up the voltage knob to 800V as read on the ISCO panel meter.
16. If the dvm shows a different voltage, adjust R100 until dvm reads 800V.
17. Power off, remove dvm, connect the dummy load at the hv terminals, (mine is 3980 Ohms @ 200W), set Voltage knob close to zero, turn the center knob to 600V 300mA, and power on again.
18. Set Voltage knob to 100%. Adjust R149 for 1250V at the panel meter, and V light just coming on.
19. Set Current knob to 100%. Adjust R153 until a current of almost 300mA is observed on the right panel meter and mA light just comes on.
20. Multiply V and mA and after turning selector to Watts, check reading on left panel meter. Adjust if needed R164 until correct power is shown.
By the above mod, the positive and negative triplers become doublers so max voltage is reduced. At the same time more mA’s become available. All current values shown on the limiter knob in 2 scales (600 and 2000V) now are still valid except that voltage is always 0-1250V. So by setting it at 600V 300mA we get 0-1250V 290mA. Before this mode you may measure voltages accros big electrolytics while unit is set to 2KV. Those caps that have low voltages usually are the leaky ones, so can be removed. 4 caps will be removed and become spares after the mode, allowing for swaps.
Good Luck!
ISCO 494 1250V 300mA MOD typo correction and TRANSFORMER POTTING
ISCO 494 MOD typo correction
Please correct step 19, the trim pot for current limit adjustment is R145 (not
R153 that adjust Watts limit).
TRANSFORMER POTTING
If you are going to use this supply in the listening room, you will notice that the transformer is very noisy. This is the procedure to make it dead quiet.
1. Cut all transformer cables going to pcb leaving 1cm at the pcb side to locate the soldering point easily later on.
2. Unscrew all transformer cables from mains terminal strip, after attaching stickers with numbers and taking notes of their positions.
3. Remove the U bracket that connects the front and rear panel and also supports the transformer. Remove the transformer. The white cylinders supporting it's front legs will stay on the pcb. Do not remove them.
4. Turn the unit upside down, rear panel facing you. Hold it like this in a big vice, that can press only the rear panel's first 2-3cm. Target: to drill holes at the rear panel. Do not use other orientation as debris can fall and remain on the pcb.
5. Take the aluminum square plate that was at the back of transformer and one silver or gold marker. Use it as a template. Mark 4 drilling points for the new position of the transformer, that will be 1 cm to the right and 0.5cm lower compared with the original positioning. This will lead the transformer 1 cm further away from the big electrolytics and 0.5cm higher from the board. You will see why soon.
6. Drill another 4 holes, right on the previous mounting screws, to destroy and remove them. Alternatively you may cut them flush. Will not be needed.
7. All holes will be 4mm, so 4 new screws approx 3cm long must be secured by a nut and washer at each transformer foot, head facing towards coils. Tighten them as the head will not be accessible later on, as the transf will be potted.
8.Using a piece 5 mm thick plywood, construct a cubic box where the transformer must fit. No upper cover needed. Make it touching the core. Use glue and staple each corner. Drill 4 holes for the transf screws. The next day put the transf inside, and secure all cables upwards and out of the box. Attach the metal plate OUTSIDE the wooden box and tighten it with nuts to hold transf in position.
9. For potting material use semi rigid tar, it comes in 5kgr cans and is used for roof isolations. This is VERY sticky, adheres to anything and creates a mess (black).
CAUTION:
If you are married the following steps must be followed when your wife is not at home!
10. Use an old pan to melt the tar. (best performed outdoors or the room will have a tar smell for several hours) Do not melt the full quantity needed, just repeat steps 10-11.
11. Very carefully (HOT!) pour the melted tar in the wooden box until it's surface just covers the core. No problem if the core is visible.
12. After some hours, you may reassemble the transfomer but before this, all leads must be lengthened. Start from the pcb side, that will not be easily accessible later.
13. The square metal plate goes on the outside of unit's case and transf is secured by nuts and lock washers from the outside.
14 The mains terminal strip must be relocated. I use only half of it.
15 Note that 2 transformer cable pairs are not needed to go to the board again and are jumpered directly (blue+orange) and white+brown in 220V configuration.
The U bracket will not be reassembled and the transf will just rest on the white plastic cylinders. So do not drop the unit!
16. This mod will make the transf VERY quiet. Good luck with tar melting!
ISCO 494 MOD typo correction
Please correct step 19, the trim pot for current limit adjustment is R145 (not
R153 that adjust Watts limit).
TRANSFORMER POTTING
If you are going to use this supply in the listening room, you will notice that the transformer is very noisy. This is the procedure to make it dead quiet.
1. Cut all transformer cables going to pcb leaving 1cm at the pcb side to locate the soldering point easily later on.
2. Unscrew all transformer cables from mains terminal strip, after attaching stickers with numbers and taking notes of their positions.
3. Remove the U bracket that connects the front and rear panel and also supports the transformer. Remove the transformer. The white cylinders supporting it's front legs will stay on the pcb. Do not remove them.
4. Turn the unit upside down, rear panel facing you. Hold it like this in a big vice, that can press only the rear panel's first 2-3cm. Target: to drill holes at the rear panel. Do not use other orientation as debris can fall and remain on the pcb.
5. Take the aluminum square plate that was at the back of transformer and one silver or gold marker. Use it as a template. Mark 4 drilling points for the new position of the transformer, that will be 1 cm to the right and 0.5cm lower compared with the original positioning. This will lead the transformer 1 cm further away from the big electrolytics and 0.5cm higher from the board. You will see why soon.
6. Drill another 4 holes, right on the previous mounting screws, to destroy and remove them. Alternatively you may cut them flush. Will not be needed.
7. All holes will be 4mm, so 4 new screws approx 3cm long must be secured by a nut and washer at each transformer foot, head facing towards coils. Tighten them as the head will not be accessible later on, as the transf will be potted.
8.Using a piece 5 mm thick plywood, construct a cubic box where the transformer must fit. No upper cover needed. Make it touching the core. Use glue and staple each corner. Drill 4 holes for the transf screws. The next day put the transf inside, and secure all cables upwards and out of the box. Attach the metal plate OUTSIDE the wooden box and tighten it with nuts to hold transf in position.
9. For potting material use semi rigid tar, it comes in 5kgr cans and is used for roof isolations. This is VERY sticky, adheres to anything and creates a mess (black).
CAUTION:
If you are married the following steps must be followed when your wife is not at home!
10. Use an old pan to melt the tar. (best performed outdoors or the room will have a tar smell for several hours) Do not melt the full quantity needed, just repeat steps 10-11.
11. Very carefully (HOT!) pour the melted tar in the wooden box until it's surface just covers the core. No problem if the core is visible.
12. After some hours, you may reassemble the transfomer but before this, all leads must be lengthened. Start from the pcb side, that will not be easily accessible later.
13. The square metal plate goes on the outside of unit's case and transf is secured by nuts and lock washers from the outside.
14 The mains terminal strip must be relocated. I use only half of it.
15 Note that 2 transformer cable pairs are not needed to go to the board again and are jumpered directly (blue+orange) and white+brown in 220V configuration.
The U bracket will not be reassembled and the transf will just rest on the white plastic cylinders. So do not drop the unit!
16. This mod will make the transf VERY quiet. Good luck with tar melting!
change main voltage on a isco 494
Hi there, by looking at tis thread on isco 494 i decided to buy one on ebay.
Now that my unit has arrived, i see that it only has one main socket at 117VAC.
I have downloaded the manual and fron what I understand it is possible to change main voltage if you have a version with 2 mains sockets.
According to your experience, is it possible to modify my unit for 230V without being forced to buy a separate trans 110-220V???
Hi there, by looking at tis thread on isco 494 i decided to buy one on ebay.
Now that my unit has arrived, i see that it only has one main socket at 117VAC.
I have downloaded the manual and fron what I understand it is possible to change main voltage if you have a version with 2 mains sockets.
According to your experience, is it possible to modify my unit for 230V without being forced to buy a separate trans 110-220V???
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