A large power resistor on my RCA 630TS is shot. This is R185a/b, a two-section jobby spec'd at 1360 ohms/17 watt and 230 ohms/10 watt.

On page 500 of the Mouser catalog, I see an Ohmite adjustable vitreous enamel resistor in various values. I haven't used this kind before.

Am I right in guessing that you can adjust the resistor down from its maximum value? For example, if I got the 1.5K/25 watt, could I adjust it down to 1360 ohms? That would be much simpler than strapping together a bunch of fixed resistors to get these odd values.

Yes, that is how they work. The Mouser catalog is pretty good...check the dimensions/drawings they display, that will tell you if the new part will fit where your old one is. I bought my horiz.lin. resistor from them not long ago and it worked great. In my case I wanted to use the adjustable but the power rating I needed was only available in a size that was too long to fit where the old one was.

There is a 1300 ohm 18w sandbox in my ctc15 clone that is impossible to get, so I have looked into this problem pretty extensively. mine was just too high in value, so in the end I shunted it. Nevertheless, here is what I learned.

The adjustable ones are just exactly how you describe, and there are clips available to mount them. Presumably they could also be post-mounted on the chassis to a screw, just like an old '50's ceramic wirewound. My old resistor was axial, and I didnt want to chassis-mount. Ditto for the aluminum cased ones that require heatsinking. What you are suggesting sounds good as long as the third terminal is there on the Mouser adjustable resistor. Is it?

There are some axial ceramic wirewound resistors in the mouser catalog, and they are much, much smaller than you would expect for the wattage. This is what I would have used if I actually replaced the resistor. It is easy to parallel stuff out of existing 10w values to get 1250ohm (ctc-12) 1300ohm (some clones) and 1400ohm (ctc15, ctc16). These are all 18w resistors.

I don't remember if they come above 10w, If not you might have to use three on one half of the resistor. If this is an old bolt mounted ceramic, I can imagine using the old resistor as a terminal strip, and coming up with a clean, non-invasive repair. The five-watt versions are very very tiny, as I recall they are about like a 1w metal film, bit slightly longer.

Best of luck,

John

A large power resistor on my RCA 630TS is shot. This is R185a/b, a two-section jobby spec'd at 1360 ohms/17 watt and 230 ohms/10 watt.

I see an Ohmite adjustable vitreous enamel resistor in various values.

Am I right in guessing that you can adjust the resistor down from its maximum value? For example, if I got the 1.5K/25 watt, could I adjust it down to 1360 ohms?

Add an extra 100 ohm power resistor to the unused end and you'd have the 230 ohm part as well. The adjustable tab becomes the tap, like on the old resistor.

Add an extra 100 ohm power resistor to the unused end and you'd have the 230 ohm part as well. The adjustable tab becomes the tap, like on the old resistor.

Say, there's a clever idea. Might save space, too.

Thanks, all.

Oh. Thats what I thought you were suggesting in the first place. I didnt notice it was 100 ohms off. D'oh!

John

Phil,

How was that resistor shot? The short in my 630TS caused me to test this resistor. It tested fine as both resistors are within tolerance. Was yours drifted too low or too high?

Thanks.

Jonathan

Phil, How was that resistor shot?

The 1360 section was open -- ceramic burned up and falling off. The other (230) section was within about 30%, but I couldn't fit a sub in the bleeder compartment without removing the big fat original and subbing both of them.

Just for the record, R185A and R185B don't share a connection, so I wasn't able to employ the trick earlier suggested by wa2ise, tacking a 100-ohm resistor on and using the slider as the center tap.

Anyhoo, I got the 1.5K adjustable resistor in the mail. The smaller adjustable is backordered until May or June (grr), but I found enough 10W resistors in the drawer to make up the other half.

Good news: we have a fine picture (well, on most channels). Bad news: crappy/absent sound everywhere, so I need to hit the books and figure out how to align the sound strip.

Later!