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  #16  
Old 08-22-2014, 08:50 AM
dieseljeep dieseljeep is offline
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Originally Posted by Winky Dink View Post
I read a number of articles and forum posts on resistance line cords.
I had already replaced the two 1200 ohm/3W resistors 1200 ohm/7W ceramics. So I only have to deal with the 566 ohm line cord resistance.



Options that have been recommended include (1) Reproduce a resistance line cord (2) Replace the 35V rectifier with a 117V rectifier (3) Replace line cord resistance with in-chassis resistance (3) Replace line cord resistance with capacitance.

Option 1 is ill-advised (for me) for a number of reasons, and I'll have to pass on option 2 because I want to preserve the original tube line-up.

Option 3 is viable because the heat can be dissipated by cutting a hole in the wooden chassis base to vent the heat into the battery compartment space. I can cobble together 3 or 4 resistors to get 560 ohms at 24 or 25 Watts.



Option 4 is the clear favorite. Informed sources recommend experimenting with estimated capacitance to achieve the desired voltage drop, but I can't do the math to even make an estimate.

Can someone give me an estimate of the capacitance needed to drop 120VAC to 35VAC?

Finally, other than a few motor-start caps, I've been unable to find nonpolar AC capacitors in Mouser, DigiKey, Allied, or the usual vintage suppliers. I'm sure they're there, but I'm probably not using the right search terms.
I've approached that problem a different way.
Install a standard line cord and use a one amp silicon diode and about a 150 ohm 5 watt resistor. Leave the tube in there, for appearance.
BTW, if you look at the newer Warwick models, they switched to a 117Z4, in the later runs.
I've also used 117Z6's, as well, but the socket has the be rewired.
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  #17  
Old 08-22-2014, 09:00 AM
dieseljeep dieseljeep is offline
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Originally Posted by dieseljeep View Post
I've approached that problem a different way.
Install a standard line cord and use a one amp silicon diode and about a 150 ohm 5 watt resistor. Leave the tube in there, for appearance.
BTW, if you look at the newer Warwick models, they switched to a 117Z4, in the later runs.
I've also used 117Z6's, as well, but the socket has the be rewired.
I messed up on my last entry!
The 150 ohm and the diode was meant to be connected from the plate and the cathode of the rectifier tube, to furnish B+. Leave the heater disconnected.
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  #18  
Old 08-22-2014, 09:06 AM
dieseljeep dieseljeep is offline
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Originally Posted by Electronic M View Post
To determine the wattage take the heater current and multiply it by (120V - the sum of the heater voltages of the tubes in series with your resistor)...Or, if I'm interpreting the info you posted correctly, 0.15A*(120-35V)=12.75W....Go with a 13W or higher replacement.

There are also ways to replace the cord with a diode or a capacitor to drop the voltage, which have the advantage of not releasing nearly as much heat. You will have to google those as I'm not experienced enough with those methods to specifically advise you off the top of my head.
Hey Tom!
Look up WA2ISE's website.
His formula for cap droppers is real easy to use and I've had great sucess with my applications.
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  #19  
Old 08-22-2014, 10:13 AM
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Winky Dink Winky Dink is offline
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I read a couple of descriptions of using a diode, but the authors came back with corrections so often that I figured I would be venturing too far into the "I Don't Really Know What I'm Doing" territory. I will look for WA2ISE's formula.
Thanks.
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  #20  
Old 08-22-2014, 10:23 AM
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Winky Dink Winky Dink is offline
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...but my antivirus blocks me from wa2ise.com.

"Website blocked!
The site contains infected code: Script.Packed.IFrame.K@gen
Virus: Script.Packed.IFrame.K@gen"

I expect that this is a false positive, but I'll have to stay off the site for now.
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Old 08-22-2014, 11:08 AM
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Quote:
Originally Posted by Winky Dink View Post
...but my antivirus blocks me from wa2ise.com.

"Website blocked!
The site contains infected code: Script.Packed.IFrame.K@gen
Virus: Script.Packed.IFrame.K@gen"

I expect that this is a false positive, but I'll have to stay off the site for now.
Ehhh, it's not impossible that's not a false-positive, better safe than sorry.


I fiddled around with things to get a preferred number value here, so if your line voltage is lower than 125.5 the current will be less than 150mA.

3.3µF works fine, 3.47µF is "exact" at 120v/60hz for 35v 150mA...




I'll leave the exercise of doing the reverse calculations up to you to figure out exactly what the current would be with a 3.3µF E6 series cap at your particular flavor of local mains.
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  #22  
Old 08-22-2014, 11:35 AM
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Winky Dink Winky Dink is offline
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Gotcha! Thanks for the lazy man's answer.
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  #23  
Old 08-22-2014, 11:56 AM
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teevee teevee is offline
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I rather like the idea of replacing the rect with a silicon diode, and doing away with the tube rect alltogether. Add series resistance to get the B+ (and fil) voltage you want..
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  #24  
Old 08-22-2014, 12:43 PM
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NoPegs NoPegs is offline
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Quote:
Originally Posted by Winky Dink View Post
Finally, other than a few motor-start caps, I've been unable to find nonpolar AC capacitors in Mouser, DigiKey, Allied, or the usual vintage suppliers. I'm sure they're there, but I'm probably not using the right search terms.
There's so much irony here... http://www.ebay.com/itm/NTE-MLR335K2...item540204913c


You can get them cheaper if you don't mind the slow-boat from Shenzhen, but I'll gladly pay the asking price for something that ships stateside at a reasonable price.

There's a learning curve to parametric searches, here's a brief crib-sheet:


The trick with Mouser's search for caps is as follows:

Head to the capacitor category, choose your flavor (electrolytic/film/ceramic/mica/lambskin/etc...) then tick the stocked box at the top, hit apply filters.

Now you pick your value, or possibly your ideal value plus one on each side. Again, hit apply filters. (Sometimes you'll pick 0.5x your value because 1x isn't a sane number, just parallel them up.)

Now we choose our voltage. I usually go with selecting the DC voltage, as many suitable caps don't actually have up-front AC rating values on them. In your case we'll start at 250VDC, then hit the > to pick anything 250 or higher. Again, apply filters. (Are you sensing a pattern here?)

Now we'll say we only want radial caps, that are good for 105C minimum, applying filters. (This is one of the few times where you can enter more than one requirement between hitting apply filters.)

Finally, since this *is* a current limiting cap, we're going to go for 5% tolerance!

Gives us 5 results, across the normal spectrum of "I'd trust it in my own home." to "Only the best will do here, Cornell Dubilier please!" pricing...

http://www.mouser.com/Passive-Compon...r&Ns=Pricing|0

In the Matsushita affordability range you even get to choose between 10mm and 15mm lead spacing! How bourgeoisie! I'd go for the 15mm unit myself.


Resistor hunting is a similar path, but you pick through-hole first, then your tolerance, then wattage, then value. I usually pre-select only Vishay branded items, resorting to random sources only if I can't find what I need from Vishay.

I still say the free shipping unit linked at the top is your best investment unless you've got a dozen or so things on your perpetual Mouser saved shopping cart ready to purchase. The Mouser order will arrive in the shortest time though, that I can assure you.
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  #25  
Old 08-22-2014, 04:22 PM
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wa2ise wa2ise is offline
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I checked my website with several URL scanners, none found anything. Doesn't mean that yours was a false positive, but I couldn't find anything. About a year and a half ago there was an infection, but I believe I was able to remove it. Did that a year and a half ago.

The result above for the cap is consistent with what my excel spreadsheet says, 3.5uF. Use one for 120VAC service.
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  #26  
Old 08-22-2014, 11:00 PM
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Winky Dink Winky Dink is offline
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Couldn't find what I needed from Mouser because I was stuck on "nonpolar electrolytic" as referenced in the Nostalgiaair link:

"The capacitor must be a special type. It's a non-polarized electrolytic. It's non-polarized to handle the AC current, and electrolytic because of the relatively high capacitance value required."

But that article was written over 20 years ago!

Regarding w2ise.com, I think my G-data software is quirky. I get blocked occasionally from innocuous sites.
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  #27  
Old 08-23-2014, 08:37 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by Winky Dink View Post
Couldn't find what I needed from Mouser because I was stuck on "nonpolar electrolytic" as referenced in the Nostalgiaair link:

"The capacitor must be a special type. It's a non-polarized electrolytic. It's non-polarized to handle the AC current, and electrolytic because of the relatively high capacitance value required."

But that article was written over 20 years ago!

Regarding w2ise.com, I think my G-data software is quirky. I get blocked occasionally from innocuous sites.
The last cap-dropper I made up was from a scrap ceiling fan.
When I see one on trash day and I have time, I remove the switch and cap assembly and leave the rest there. They have two AC caps of different values.
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  #28  
Old 08-24-2014, 02:38 PM
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The cap should be a film or such, electrolytics may overheat, and tend to not be an accurate value. And get one designed for service across the powerline, usually they say "250VAC". Fan caps are good for this, think I saw them at Home Depot.
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  #29  
Old 08-24-2014, 06:37 PM
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Winky Dink Winky Dink is offline
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I'll take a look in the home stores. In the meantime, I hooked up the set with ceramics, powered it up with the variac. The 7-watt ceramics I used to replace the original 3-watt resistors inside the chassis got much hotter than I would have expected. I think that so much heat in a small chassis really cooked all the components that I had to replace.
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  #30  
Old 08-24-2014, 07:14 PM
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Look at Parts Express, Electronic Goldmine, and the other semi-surplus sites. I have often found them there, cheap cheap.
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