N9axl
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« on: August 28, 2015, 11:30:58 AM » |
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I started working on this Ranger. It actually is cleaner than I thought it would be, no obvious burned parts -- clearly a kit build due to the nuts and bolts on the tube sockets. No obvious missing parts - although the VFO seems disconnected which is interesting. I plan to do that last.
Now, this calls for some 700V electrolytics which are no longer made. I can put some in series and get the right values, but I wonder -- would it be worthwhile to put in really high voltage caps -- say 1000 or 2000V -- just so I never have to ever replace these again.
I figure that having a 1600V cap where it asks for 400V means this thing will just loaf and there would be less issues with voltage spikes or as the caps age. i would rather not have a cap fry down the way and take a transformer which would be much harder to replace.
It's probably complete over engineering, but will it negatively affect performance?
Any issues with this strategy?
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N8ETQ
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Mort
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« Reply #1 on: August 28, 2015, 11:38:11 AM » |
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Hi,
I opened one of those once and it was just 2 caps in series with no balancing "R"'s, just use a pair of 450 V jobs in series with a couple of 270k R's to split the load.
Once the electric companies raise the line voltage to 130V then you could consider higher voltage. You may want to check your Fil. voltage. It's going up too!
GL
/Dan
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KA2DZT
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« Reply #2 on: August 28, 2015, 11:38:56 AM » |
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Using single caps (1000V) is always better than using two caps in series. Do they make 1000 volt electrolytics?
Fred
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w1vtp
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« Reply #3 on: August 28, 2015, 01:18:46 PM » |
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I vote for using two caps in series with eq... resistors in case one has a tad more leakage than the other. I don't see the value in doing overkill in the WVDC dept.
I have included the before and after with my Viking 1. The new caps are MUCH smaller.
Al
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N9axl
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« Reply #4 on: August 28, 2015, 01:28:56 PM » |
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How do you do the eq. resistors? Are they in series with the cap? On the negative end or in parallel? What values? and wattage?
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w1vtp
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« Reply #5 on: August 28, 2015, 01:35:28 PM » |
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How do you do the eq. resistors? Are they in series with the cap? On the negative end or in parallel? What values? and wattage?
Right across each individual cap... Doesn't need to draw a lot of power but the resistor should be non-carbon comp... types and sufficiently rated to handle the power. The idea is to draw enough power with the EQ resistors to make any difference in cap... leakage a non-issue. 220 Kohm. use OHM's law to figure what wattage will be dissipated across each resistor and double the wattage for the EQ resistor. Al
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w4bfs
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« Reply #6 on: August 28, 2015, 02:02:40 PM » |
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How do you do the eq. resistors? Are they in series with the cap? On the negative end or in parallel? What values? and wattage?
Right across each individual cap... Doesn't need to draw a lot of power but the resistor should be non-carbon comp... types and sufficiently rated to handle the power. The idea is to draw enough power with the EQ resistors to make any difference in cap... leakage a non-issue. 220 Kohm. use OHM's law to figure what wattage will be dissipated across each resistor and double the wattage for the EQ resistor. Al Al's got it right because modern electrolytics tend to have low leakage currents .... when you make up your assembly set up your multimeter to measure dc voltage ... make sure you have enough range in the meter to measure these high voltages, ground the negative lead to the chassis with a clip lead and measure the voltage drop across the capacitor with its negative end grounded .... say for example you read 350Vdc.... note that and CAREFULLY move the negative probe to the negative end of the second capacitor and measure the voltage drop of it ....say for example you read 340 Vdc .... this says that the caps are sharing the voltage drop almost equally and if you used 450Vdc capacitors that everything would copasetic if you see a wide difference in Vdrops then something is wrong and needs attention
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Beefus
O would some power the gift give us to see ourselves as others see us. It would from many blunders free us. Robert Burns
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N9axl
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« Reply #7 on: August 28, 2015, 03:39:45 PM » |
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OK. I will figure out the resistance needed. Since I can't buy 750V electrolytics I plan to put two 20mf 450 v in series which will give me 10mf at 900 v. Not as good as a single unit but those don't seem to be available. In general the values for the Ranger don't seem to be available but I am substituting as close as possible e.g. .005mf 400V I am using a .0056 3000 volt orange drop SBE, .02 1600 volt is replaced by .022 6000 volt. 10uf dual cap 50v replaced with 10mf dual cap 450V
Overengineering but I'd rather do that than have to do some more repair work down the line. $25 in parts now better than $100 for a transformer later. I agree it's probably more than needed but why not...
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KA2DZT
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« Reply #9 on: August 28, 2015, 11:58:36 PM » |
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OK. I will figure out the resistance needed. Since I can't buy 750V electrolytics I plan to put two 20mf 450 v in series which will give me 10mf at 900 v. Not as good as a single unit but those don't seem to be available. In general the values for the Ranger don't seem to be available but I am substituting as close as possible e.g. .005mf 400V I am using a .0056 3000 volt orange drop SBE, .02 1600 volt is replaced by .022 6000 volt. 10uf dual cap 50v replaced with 10mf dual cap 450V
Overengineering but I'd rather do that than have to do some more repair work down the line. $25 in parts now better than $100 for a transformer later. I agree it's probably more than needed but why not...
You need more than 10mfd. Use two 40mfd or larger, two 80mfd in series would be better. The caps are much smaller than the originals, so you should have room for them. The equalizing resistors should be as low a value as possible. 100k would be a good value to use. Too high of a value and you begin to defeat the equalizing affect. Fred
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w4bfs
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« Reply #10 on: August 29, 2015, 02:28:33 PM » |
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with solid stating the supplies and adding capacitance you will add much strain to the already marginal function switch .... add step start to remedy
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Beefus
O would some power the gift give us to see ourselves as others see us. It would from many blunders free us. Robert Burns
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W0GSQ
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« Reply #11 on: September 02, 2015, 11:25:41 AM » |
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How do you do the eq. resistors? Are they in series with the cap? On the negative end or in parallel? What values? and wattage?
Right across each individual cap... Doesn't need to draw a lot of power but the resistor should be non-carbon comp... types and sufficiently rated to handle the power. The idea is to draw enough power with the EQ resistors to make any difference in cap... leakage a non-issue. Good advice! I replaced the "high voltage" cap in my Johnson Adventurer a couple of years ago using EQ resistors for cheap insurance. When I took the old cap out I used a X-Acto knife to cut one of the end crimps off of the cardboard tube and pulled out the guts, nothing in there but two caps in series with no resistors, low tech solution in a fancy cardboard tube but it did work just fine for at least 50 years. 220 Kohm. use OHM's law to figure what wattage will be dissipated across each resistor and double the wattage for the EQ resistor. Al
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K9DXL
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« Reply #12 on: September 02, 2015, 01:11:18 PM » |
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A couple of good points already mentioned. With your solid state power supply, consider adding a current inrush limiter to make life easier for those older components. Also consider powering the rig from a Variac or bucking transformer to lower your house AC line voltage a bit. My outlets test at about 122 VAC, which I reduce to between 112 - 115, and my vintage rigs do just fine on that.
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Breathing solder fumes since 1959. That explains a lot.
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W0GSQ
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« Reply #13 on: September 03, 2015, 10:31:31 AM » |
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Good advice! I replaced the "high voltage" cap in my Johnson Adventurer a couple of years ago using EQ resistors for cheap insurance. When I took the old cap out I used a X-Acto knife to cut one of the end crimps off of the cardboard tube and pulled out the guts, nothing in there but two caps in series with no resistors, low tech solution in a fancy cardboard tube but it did work just fine for at least 50 years.
My post got mixed into Al's quote, sorry!
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