The International Cessna^® 170 Association

You're welcome Eric. Let us know if that thing gets hot. Also, does it turn off all the way? I can't remember.
Max

It turns all the way down til you can't see the light anymore. I have a seperate on/off switch for the panel lights -- one of the piano keys-- so the dimmer feature is all I care about.
From what I've read on these forums, you can provide a true "off" position (as opposed to "dimmed down to nothing") by dabbing some nail polish or something similar at one end of the windings. When the brush rests on that, the switch is really "off". Otherwise, I guess it's still doing whatever it does with the current, and still generating heat.

Eric

FWIW, the dimmer/rheostat I replaced was a "Clarostat". The p/n itself is obscured, but it's rated at 50 ohm,25 watt nominal, and (I think) 0.77amps max. It's approximately the same size as the Ohmite replacement, but is fully enclosed-- no exposed windings. Has two #8-32 screw lugs on the back, & mounts thru a 3/8" hole, using the same knob as the Ohmite. Pretty nicely made unit.
I found Clarostat on the internet, but couldn't come up with anything very close to what I've got, at least without a part number.

Eric

I ran across AD 93-24-15 today. Stumbling onto this AD really struck me as to how difficult it is to do a thorough AD search on 60 year old aircraft. I was curious why the C-170 series was not included in this AD as it applies to the early model 150/172/180/185 which probably use a similar if not the same rheostat. It turns out that this applies to the dimmer rheostats that are mounted on the ceiling. There is a danger of them lighting the headliner on fire. Talk about a hot-headed pilot! Interestingly, my 170 project came with this "upgraded" dimmer rheostat/instrument panel light assembly which is the subject of this AD. It's possible that there are others out there with this potentially hazardous "upgrade" that should be removed or modified. Cessna SEB 92-33R2 details what needs to be done to comply with the AD. The kicker is that the called for replacement rheostat is $1988 from Aircraft Spruce! A cheaper, yet still expensive, alternative is to use a MaxDim rheostat which apparently complies with the AD. Cheaper still is to go back to the original configuration on your 170. If the moderators want SEB 92-33R2 in the Mx Library I can post it there.

The electronic dimmers can overheat and cause fires. They are not the simple resistance-wire rheostats originally found in 170's.

I removed the panel light dimmer from my '48 C170, so if anyone would like to give it a new home, feel free to make a reasonable offer. It worked when removed and I have no reason to believe it's not original equipment. That said, I'll gladly send pix and part numbers to anyone who asks so you can verify for yourself.