The PHILCO Phorum
Resistor replacement - Printable Version

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Resistor replacement - RF7590 - 02-10-2015

Hello all,
 
  have read the phorum for quite a while but have never posted anything before.
Decided I need a little advice. I have restored and or worked on a fair amount of equipment over the years but am new to working on antique radios.

I am currently working on a 46-421. I have cleaned up the chassis, replaced all the caps and the power cord.
Now on to the resistors. I found three that are out of spec. 
A 130, 470k, and 3.3M, this is where my questions come.

These all look to be carbon comp. resistors, should I replace with carbon comp. or go with something like flame-proof modern style resistors?

If flame-proof, should I use 1/2w or go up to 1w?

Any suggestions for a good place to buy new resistors that will work good on tube radios?
I'm having a hard time finding a 3.3M resistor. I don't want to solder resistors together to get the right value.


Thanks

RF

RE: Resistor replacement - morzh - 02-10-2015

1. Go with whatever the cheapes one you find, a metal film 5% is just fine.
2. No need for flame proof. If you get flames, you got worse problems, and adequately power rated resistor is all you need.
3. Calculate the wattage by U-square over R rule, you should know the dropout across the resistor. I use 1W for everything above 50K indiscriminately and for lower values I calculate the wattage.
4. It is rarely you need a resistor of 3.3M value to be very accurate. 10-20% is likely OK. However in Mouser there is plenty of 3.3M axials and one from Vishay 1/2W (which is plenty) is 13 cents stock.

RE: Resistor replacement - codefox1 - 02-10-2015

Agree, trend among may restorers is to replace old carbon resistors as well as just about all capacitors when going through a set. Many suppliers have assortments of differrent value resistors which brings down unit price to pennies,
and modern 1 or 2 watters are small as old 1/2 watt units, so never a space issue. I'd stick with 1/2 watt replacements wherever they are used as "fusisters" for damage control. As for high value (over 1 meg,) these can creep up a lot and become unreliable, so I always replace 'em.

RE: Resistor replacement - klondike98 - 02-10-2015

Welcome to the Phorum!  You'll find some suppliers on the Resources Pages.

RE: Resistor replacement - RF7590 - 02-14-2015

Thanks to all who replied. Parts have been ordered, and restoration continues.

RF

RE: Resistor replacement - OldRestorer - 02-14-2015

gosh,

I am afraid of resistor replacement. I have purchased a full assortment but have yet to replace one. I just cant get over the fear hurdle. I guess it is he lack of knowledge about exactly what you are asking. Should be easy once I learn but cap replacement seems so much easier...

Kirk

RE: Resistor replacement - morzh - 02-14-2015

Why are you afraid? Same two-pin passive part, and same reliability when comes to soldering. Power calc, you can always ask here, or for regular dogbone go with 1W across the board and larger - ask here.
Measuring in circuit in tube sch is quite possible with rare exceptions, typically a reistor, in 95% cases will go to a tube electode which when power is off is as good as disconnected so the measurement is usually correct without biting it off/unsoldering.

RE: Resistor replacement - sam - 02-14-2015

mike
come on your talking about kirk Icon_crazy Icon_e_wink
sam

RE: Resistor replacement - morzh - 02-14-2015

I heard falling off roofs sometimes produces a syndrome known as "resistophobia".
At the same time it induces an inexplicable infatuation with capacitors, as well as with rodent-damaged pieces of technology.

RE: Resistor replacement - markmokris - 03-10-2015

(02-14-2015, 06:09 PM)morzh Wrote:  I heard falling off roofs sometimes produces a syndrome known as "resistophobia".
At the same time it induces an inexplicable infatuation with capacitors, as well as with rodent-damaged pieces of technology.

I can see the fear that comes from modern 1/2 watt resistors being so tiny.  Seems like there just can't be enough resistance/wattage in that little thing you are soldering in.

Icon_biggrin

Mark

RE: Resistor replacement - PAradiogeek - 03-10-2015

I started off buying resistors with different power ratings. Now, I'm working through my stock of lower wattage resistors. Going forward, everything will be 2W. It is easier to buy and stock one type, and 2W covers about 99% of what is needed.