Resistors

[ThSpeakerDude88]

I'm restoring a 1936 RCA 5T superhet, need to know if I can replace the wire-wound resistors with regular ones, and if so what wattage I need.

Thanks!

~TSD88

[anatech]

Hi ThSpeakerDude88,
Yes you can replace those with regular ceramic or carbon. Many higher power resistors (5~10 W bathtub) are wire wound. If the power rating isn't stated in the schematic, calculate from the value (X ohms) and measured voltage drop. I like to go at least 4X the value.

-Chris

[ThSpeakerDude88]

ok thanks. One quick question: How do I re-wire the power cord?

Its wired into one lead of the transformer and then the other one goes to the switch , which in turn goes back into the transformer, thus activating the primary. I want to use a polarized plug. Should the switch be wired with the Large Spade on the plug or the small one?

[Original Burnedfingers]

Small is hot, larger is neutral, round is ground. When changing to a three wire/plug the round or ground is taken to a chassis connection. A three wire/plug will provide extra safety.

Yes, keep the switch on the hot leg.

[Original Burnedfingers]

I like to go at least 4X the value.

Chris,

That is a good point especially when dealing with tubes circuits.

I can remember fixing many a Altec Lansing product and finding the reason I was loosing a particular resistor was the fact the engineer figures the wattage rating incorrectly. I can remember the Altec 9442 power amplifier that used a 1/2 watt resistor where the current on that resistor was almost a 1/2 watt. Didn't last long enough to get thru warranty or would die shortly after. I never did get them to admit they made an error but I did receive a package of 1 watt resistors. Funny thing is shortly after I talked to them they made an engineering change. Its funny how they had never experienced a problem before I brought it to their attention.

[anatech]

Ahhh, we aren't having any problems .....

How many times has that happened? Marantz did it, Carver did it and the Japanese will never admit to anything. (Teac / Tascam have threated me in the past) Is it so hard to say thanks to a tech?

Actually, the engineers at the old Carver company did thank techs that found problems - and came clean. Adcom were open to discussion as well.

Interestingly, most companies have made errors in this way. Trust your common sense and your insterments people.

-Chris

[ThSpeakerDude88]

I checked the old parts listing that came in the original owners manual, and to my surprise found all the resistors are 1/4 watt! with the exception of cource of two 1/2 watt ones and one 1 watt one. It says carbon type, so I'm assuming that if I measure the voltage and make sure the 1/4 watt is fine, I can use resistors from the 500 peice grab bag I got at the Shack?

[anatech]

Hi,
Yes, from the voltage you can figure out the current and thus, the power. If an original part looks like it's been warm, up the wattage. Be aware that carbon film types do not handle surges well, for those use metal oxide, molded carbon comp or wire wound.

-Chris

[ThSpeakerDude88]

ok thanks. The resistors, aside from being a bit dirty with age, they look like their in good shape and have not gotten warm.

[anatech]

Well. don't just sit there! Change them!

-Just kidding, take your time, Chris