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
Thanks!
~TSD88
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
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
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?
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?
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.
Yes, keep the switch on the hot leg.
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.
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.
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
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
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?
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
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
ok thanks. The resistors, aside from being a bit dirty with age, they look like their in good shape and have not gotten warm.
hahaha ok I will 🙄
I do however need to find some 1/2 watt and 1 watt ones at radio shack. Also need to know where I can order these capacitors for cheap
.25 uf 200v
.1 uf 200v
.005 uf 500v
.010 uf 500v
47 uf and 80 uf 450 volt filter caps (I'm assuming its ok to have larger value filter caps)
I do however need to find some 1/2 watt and 1 watt ones at radio shack. Also need to know where I can order these capacitors for cheap
.25 uf 200v
.1 uf 200v
.005 uf 500v
.010 uf 500v
47 uf and 80 uf 450 volt filter caps (I'm assuming its ok to have larger value filter caps)
Hi ThSpeakerDude88,
Not too much larger on the filter caps. Observe the max. capacitance value for your rectifier. Normally, this will not exceed 50uF, and that's for a 5U4GB. The original values should work for you.
Antique Radio has most of these parts, larger jobbers will have them as well. To be honest, I don't use Radio Shack for much.
-Chris
Not too much larger on the filter caps. Observe the max. capacitance value for your rectifier. Normally, this will not exceed 50uF, and that's for a 5U4GB. The original values should work for you.
Antique Radio has most of these parts, larger jobbers will have them as well. To be honest, I don't use Radio Shack for much.
-Chris
yes, just about the only thing I can get there for this project is wires and resistors, and maybe a pot or two.
The original schematic called for 10 uf and 18 uf filter caps, the replaced ones are labled 20 and 50.
The rectifier is a full wave RCA-80
Someone has put diodes on the two power leads to it, then from those to a big multi-lead ceramic resistor, then the resistor is attached to the field coil and one end of a filter cap.
What in the world do you think this is for?
The original schematic called for 10 uf and 18 uf filter caps, the replaced ones are labled 20 and 50.
The rectifier is a full wave RCA-80
Someone has put diodes on the two power leads to it, then from those to a big multi-lead ceramic resistor, then the resistor is attached to the field coil and one end of a filter cap.
What in the world do you think this is for?
I remember seeing a multi leaded resistor in my radio, attached to the rectifier tube. I think that my RCA used an 01V rectifier, although I might have it confused with another radio, it was last year when I fixed it. I did a google search on the model number, and found the schematic. It was on an antique radio web site.
To answer you I would need to look at the schematic and a picture of what they did. Anything else is a guess.
Depending on the wiring, the diodes may bypass the rectifier (#80) and the resistor would be to drop some excess voltage. Could be a "good idea" also. I'd like to study it more first.
The caps should be the original size within reason. 50uF isn't too lage for the 80 I don't think, but you would not want to go higher.
-Chris
Depending on the wiring, the diodes may bypass the rectifier (#80) and the resistor would be to drop some excess voltage. Could be a "good idea" also. I'd like to study it more first.
The caps should be the original size within reason. 50uF isn't too lage for the 80 I don't think, but you would not want to go higher.
-Chris
ok thanks. I have a 47uf mallory that I'm going to replace it with, it came out of a working tabletop radio and its a newer cap ( late 60's early 70's)
I will see if I can write out a schematic of what they did and post it on here along with the original!
🙂
I will see if I can write out a schematic of what they did and post it on here along with the original!
🙂
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