M20J panel dimmer switch project - worn dimmers need to be replaced

[BrianW]

Hi,

I'd like to share my journey...

I have a 1979 M20J. I am an owner pilot and engineer. I want to keep my M20J as original as possible. So, here's my next "squeaky wheel" in my plane - the worn-out dimmer switches. My dimmers are now around 47 years old. That's a great service-life for a moving component! But alas, the old dimmers are no longer smoothly dimming. The dimmer adjustment has "dead spots" and need "finessing" to operate. 

I know there are some here that love paying lots of money for "its aviation, you need to add one or two zeros to the price". But I'd rather find the exact replacement part for $9 if they are available. And that brings me to my project...

Looking at the Mooney Service Manual and wiring diagrams for my serial number, the dimmers are standard common parts. Or least they were back in 1979!

The dimmer consists of a rheostat (potentiometer) and resistor. The rheostat was produced by Allen Bradley which stopped production over 20 years ago. The rheostat (potentiometer) cannot even be located in used parts or secondary resellers (i.e. eBay, etc.). The resistor is likewise unavailable anywhere.

At least the company producing the resistor is still in business - Ohmite Manufacturing. I was able to find Ohmite's cross reference from legacy part numbers to their new part numbers.

Using engineering data for the original resistor and potentiometer, I was able to confirm the new resistor part number is the identical component.

The specifications for the potentiometer made it challenging to locate an identical commercially available replacement part. With lots of searching I was able to eventually locate a manufacturer in the US that produces aerospace parts and has a commercially available equivalent potentiometer. It is operationally identical; the only real difference is the control shaft is a 1/8 of an inch longer than the original Allen Bradley potentiometer switch (meaning the dimmer control knob would just stick out 1/8" further from the panel).

I put a call into the local FSDO to get their feedback. I spoke with their inspector and was told several methods to make sure that the replacement is compliant.

I asked, as the owner and pilot if I could replace the dimmer as "Preventive Maintenance" since these are common parts and do not involve complex assembly. I felt that if the PMA dimmer switches at Aircraft Spruce state that the Owner/Pilot can install their PMA dimmer switch with only a logbook entry, then replacement of dimmers are not considered complex and do not require FAA certified installers or special inspections.

The FSDO inspector felt the question of "owner/pilot replacement as preventive maintenance" was a good question. He didn't know the answer to that off the top of his head. We discussed possible compliant routes to getting the dimmer replaced. He mentioned that if it was installed by an A&P with a 337 then it would be compliant.  I definitely agreed that the 337 route is a solution that I'm considering.

Another solution that I considered was getting it PMA approved. That's a lot more work but I was thinking of potentially doing this as a small business, assuming that other Mooney owners have worn out dimmers with no other option other than expensive PMA solid state dimmers.

The inspector also said that if the manufacturer allowed these as substitute part numbers, then it would be considered part of the type certificate and be considered approved replacement parts.

With Mooney struggling to remain open and with so many Mooney Corporate changes, I don't know if Mooney is actively operating at this point in time. However, I put a call into Mooney technical support and left a message for a call back. I don't know if that will yield any results.

I'm sure that I can get this done in accordance with regs. I am just looking for the least cost (and fun) solution.

I'll post an update if I move ahead with this.

[PT20J]

It's a standard part. Replacing it with an equivalent form, fit and function standard part shouldn't be an issue. If you are concerned about signing the logbook, just discuss it with your friendly A&P and get them to supervise you and sign it off.

[EricJ]

+1 that it's a standard part.   It's also, imho, a minor modification and does not require a 337 even if the part is slightly different but functionally equivalent.   It doesn't even really need to have the same taper (i.e., dimming profile) as the original, just the same resistance range, if you don't mind the difference in dimming profile.    Likewise any resistor of the same resistance and wattage and form factor should be fine, as that's also a standard part.

The pot should have at least the same power (Wattage) dissipation capability as the previous.

The FSDO is often not a reliable source.   You'll get the opinion of whoever you're talking to at the time, and the next time you call you may get a different opinion from somebody else.   Unless the FSDO person you're talking to will be directly involved in your project and either personally inspecting or signing something off, your IA has the opinion that matters.

[N201MKTurbo]

Rely on the hangar fairies. They come in, in the middle of the night and magically fix things. They make them just like brand new. 
 

Do you think an IA or an FAA inspector is going to walk by your airplane, notice your dimmer works perfectly and has a brand new potentiometer, and knowing that it should be old and crappy, demands that you prove that that is the original pot? 
 

Just make sure your hangar fairies know what they are doing. If they do crap work, the IA might notice.

[MikeOH]

@BrianW

For further support, are you familiar with the Coleal LOI: 

Coleal-Bombardier Learjet_2009_Legal_Interpretation.pdf

[BrianW]

On 2/7/2026 at 11:11 AM, MikeOH said:

@BrianW

For further support, are you familiar with the Coleal LOI: 

Coleal-Bombardier Learjet_2009_Legal_Interpretation.pdf 649 kB · 7 downloads

Thank you for the additional information.

I read through the FAA interpretation letter and on the surface, it states that in 14 C.F.R. part 43, appendix A, paragraph ( c ). the 32 subparagraphs that define the preventive maintenance tasks are not considered "controlling" or limiting of all the potential preventive maintenance tasks, the 32 subparagraphs are considered as examples of preventive maintenance tasks.

The FAA letter further states, "Advisory Circular 43-l2A, Preventive Maintenance (which was referenced in Mr. Hernandez's letter), is overly restrictive. That sentence, found in Paragraph 3(b)(l), states: "If a task or maintenance function does not appear in the list, it is not preventive maintenance." As with the other paragraphs of Appendix A (i.e., on major repairs and major alterations), the lists are better viewed as examples of the tasks in each category-they cannot be considered all inclusive. There are, no doubt, many "simple or minor preservation operations [tasks]" and many "replacement[ s] of small standard parts not involving complex assembly operations" performed daily, especially on small general aviation aircraft, that the agency would consider to be preventive maintenance, though they are not included in the 32 listed items".

That is an excellent section of the letter.

I am now looking at an intriguing "rabbit hole" and deciding whether to jump down the rabbit hole. The letter states, "It is our understanding that Flight Standards' Aircraft Maintenance Division is planning to clarify this issue in a future revision to the AC".  Was there a clarifying AC that was subsequently released?

[MikeOH]

3 minutes ago, BrianW said:

I am now looking at an intriguing "rabbit hole" and deciding whether to jump down the rabbit hole. The letter states, "It is our understanding that Flight Standards' Aircraft Maintenance Division is planning to clarify this issue in a future revision to the AC".  Was there a clarifying AC that was subsequently released?

CAVEAT: I am NOT a lawyer and the following is NOT legal advice!   Understand that ACs are advisory, not legally binding, while LOIs issued by the Chief Counsel are.  E.g. the Coleal LOI.

Here is ChatGPT's summary, FWIW:

"FAA Advisory Circulars (ACs) do not carry the same legal weight as a Letter of Interpretation (LOI) issued by the FAA Chief Counsel's office. Here's the key difference:

• Advisory Circulars (ACs): These are issued to provide guidance, recommendations, and clarifications on specific regulations or technical procedures. They are generally non-binding, meaning they don't carry the force of law. While they are influential and often followed as best practices, they do not have the legal status of regulations or interpretations.
• Letters of Interpretation (LOIs): These are binding legal opinions provided by the FAA's Chief Counsel or other legal authorities. LOIs are issued in response to specific legal questions or issues and provide an official interpretation of FAA regulations. They hold legal weight because they represent the FAA's official stance on how certain rules should be applied in specific circumstances.

So, while ACs are useful for guidance, LOIs are authoritative and legally binding, often used in legal contexts or enforcement actions."

[BrianW]

Thanks Mike. That's more great information.

[EricJ]

On 2/8/2026 at 2:22 PM, BrianW said:

I am now looking at an intriguing "rabbit hole" and deciding whether to jump down the rabbit hole. The letter states, "It is our understanding that Flight Standards' Aircraft Maintenance Division is planning to clarify this issue in a future revision to the AC".  Was there a clarifying AC that was subsequently released?

There has been no follow-up or additional clarification of which I'm aware.    The Coleal letter is still referenced frequently when discussing Preventive Maintenance, so if there has been a clarification or update it is essentially never referenced or cited.

[BrianW]

For the benefit of others, I've attached the original Mooney electrical schematics for the M20J (for my serial number range).

I've marked up the drawing to trace out the panel light circuits and to identify what is being dimmed.

One discovery that I made from the drawing is that the compass light is connected to the on-off switch portion of the dimmer. That means that when the dimmer clicks on, the compass light gets full 14v power but cannot be dimmed.

The other goofy thing was the center console lamp. The console lamp is on the glareshield dimmer circuit. That's weird because unless you fly with the glareshield on, your center console lamp will be off.

I need to verify if the console light is the light for the flaps indicator. It that the same for other M20J owners?

I understand why the glareshield would be separately controlled from the rest of the panel lights (because I normally don't fly at night with the glareshield on). But I can't think of a reason why Mooney wanted the console light to be grouped with the glareshield and separate from the rest of the panel instrument lights.

I would think it makes more sense for the center console light be grouped with the rest of the panel lights and then the glareshield would be on its own dimmer control circuit.

Additionally, I would prefer that the power to the compass be dimmable, so that if you had a bright compass light, you could dim the brightness down to protect your night vision.

 M20J Schematics Dimmer Markup.pdf

Edited February 12 by BrianW

[Yetti]

If you know how to solder and have a Weller solder station then you are probably ahead of 90% of A/Ps.   This would fall into the can you make it as good or better than factory and the wings won't fall off if you screw it up category.   Just grind the extra 1/8" off the shaft.   One other upgrade would be get some knobs with set screws.   print some new placards for the knobs.   or pull the old placards out and glue to the new knobs.

Some people have reported the transistors dying and needing replacing which is also a common Digikey part.

On the transistor board above the wheel well you would find the transistor board with mini Buss fuses that are $$

Replacing the transistor board with some PWM modules would be better.

 

[Justin Schmidt]

The transistor circuits are also incorrect. they are high side with npn.

[BrianW]

14 hours ago, Justin Schmidt said:

The transistor circuits are also incorrect. they are high side with npn.

Can you explain what you mean by "they are high side with npn"?

The drawing showing the resistor 2N2016 looked like an error to me.  It seemed emitter "E" and the collector "C" were reversed. I scrutinized the schematic drawing tracing the positive and negative leads. I also reviewed NPN and PNP transistors and the designed current flow directions for these transistors (and correct me if I'm wrong):

In an NPN transistor, the current flows from the collector "C" to the emitter "E" when the voltage on the Base "B" goes from 0 to positive.

In an PNP transistor, the current flows from the emitter "E" to the collector "C" when the voltage on the Base "B" goes from positive to 0.

So, the current flow direction and the labelling of C and E of the RCA 2N2016 transistor appears correct.

But the Delco 2N3079 transistor (for later model serial numbers, s/n 24-0927 and on) seemed wrong. The Delco 2N3079 is an NPN transistor as well, but it has the C and E terminals reversed in the Mooney schematic, as if it was a PNP transistor. But in that case the B terminal would need to go from positive voltage to 0V in order for the lights to come on which is opposite from the way the dimmer potentiometer is wired (the panels lights do not come on when the dimmer is switched off).

So, the current flow direction and the labelling of C and E of the Delco 2N3079 transistor appears incorrect.

I will check my M20J today to see if my original transistors are RCA or Delco. Hopefully they are the RCA's.

[BrianW]

I looked under the copilot panel at the dimmer switches and did not see the transistors there. I only saw the wires from the dimmer potentiometers going to the black wire harness connector.

On the other side of the copilot panel, below the circuit breaker panel, I saw the 4 mini fuses but did not see any transistors around them.

Where are these transistors typically located? My plane is a 1979 M20J.

I just want to confirm whether I have RCA or Delco transistors.

Thanks.

[MikeOH]

3 hours ago, BrianW said:

Where are these transistors typically located? My plane is a 1979 M20J.

@BrianW

I have an 1970 F model and they are just under the glareshield on the pilot's side.  I know it's not a J, but since you are having trouble finding them...it is someplace else to look

[Justin Schmidt]

9 hours ago, BrianW said:

Can you explain what you mean by "they are high side with npn"?

The drawing showing the resistor 2N2016 looked like an error to me.  It seemed emitter "E" and the collector "C" were reversed. I scrutinized the schematic drawing tracing the positive and negative leads. I also reviewed NPN and PNP transistors and the designed current flow directions for these transistors (and correct me if I'm wrong):

In an NPN transistor, the current flows from the collector "C" to the emitter "E" when the voltage on the Base "B" goes from 0 to positive.

In an PNP transistor, the current flows from the emitter "E" to the collector "C" when the voltage on the Base "B" goes from positive to 0.

So, the current flow direction and the labelling of C and E of the RCA 2N2016 transistor appears correct.

But the Delco 2N3079 transistor (for later model serial numbers, s/n 24-0927 and on) seemed wrong. The Delco 2N3079 is an NPN transistor as well, but it has the C and E terminals reversed in the Mooney schematic, as if it was a PNP transistor. But in that case the B terminal would need to go from positive voltage to 0V in order for the lights to come on which is opposite from the way the dimmer potentiometer is wired (the panels lights do not come on when the dimmer is switched off).

So, the current flow direction and the labelling of C and E of the Delco 2N3079 transistor appears incorrect.

I will check my M20J today to see if my original transistors are RCA or Delco. Hopefully they are the RCA's.

So without going through all the college level theory of operation I will "attempt" to explain simply. 
So when we say "high side" or "low side" that is where the transistor is in relation to supply voltage and common (chassis ground in our case). Aircraft, "most" automobiles, boats generally use high side as our grounding system is the chassis and is actually safer. Our radios (ie light in KX170B or other instruments) are internally connected to chassis ground while the input expects voltage. There are some exceptions where I have seen both ends of the light brought out to the connector. 

I am going to say my disclaimer, I am going by the schematics I have SCI-800269L Rev F 10/1/82 and Maintenance Manual #106 1968-1984. Also Mooney has changed this circuit a few times, don't think they had an electrical engineer that understood transistors. For the Vintage I can understand that as they were still "new" in usage which is why, I would reckon pre '75 didn't have dimmer circuits.
A little note on Germanium transistors: part of the issues with these circuits are as Germanium ages it breaks down causing leakage on top of their higher leakage than silicon, essentially the transistor does not operate as designed. Use the silicon versions of all transistors.
I have never seen, in a textbook or otherwise, a NPN BJT situated like this (first design). High side and emitter to supply voltage (improper emitter follower aka common collector). Highly inefficient (voltage loss at Vemitter, Vce, rheostat; both transistor and rheo get hot), can’t saturate (Vb must be > Ve). Due to the voltage loss from the orientation there is very limited dimming range and not smooth, just flat out wrong. 

If using an NPN in a high side situation, usually a PNP is used, a proper emitter follower is constructed, collector to 12V, emitter to load. Still inefficient power dissipation but less voltage loss. The PNP is better in this instance as it dissipates more power while bright than while dim (we like it dim, well I do) while NPN is opposite.

The second circuit they used caught a problem with the first, No base pull down resistor in the first. If the base is left floating it may/will remain on. They still had an improper emitter follower. 

With the J’s (24-0071 and on and an SB for SOME prior C, E, F) they changed to a strange configuration of a Darlington pair. Using One Rheo, the strange part is the output of one transistor feeds a load and not just the base of the other transistor. I surmise to split current load to use the same NPN as prior.

Why they didn’t use a BJT to drive a MOSFET from the beginning, much less power dissipation, larger smoother range. like I said I guess they were not up to speed with proper transistor function, money maybe a few more parts.

Mine in an F was stuffed in the center by the firewall. Somebody completely F’ed up wiring and such. I have seen them in a box with the dimmers in the console. They usually have unabtanium little fuses.

I am in the midst of rectifying (HAHA I had to) the issues with a proper BJT/MOSFET design on mine. I think I need to get field approval.

On PWM if you go that route, Be very careful with these even the PMA MaxDim. While they are very efficient and how dimmers are now, especially for LEDs (they only option). They commonly introduce noise into the system as our systems/radios (ex170B) are not designed for it. I have seen lots of noisy systems particularly interference on 170B radios from PWM dimmers. 

So in summary for you, ensure the resistor is there base to ground, Mooney had these at the Rheostat. You can check the transistor out of circuit with DMM if you know how but I would just replace them with current silicon 2N3055 w/heatsinks. The 2N2016 should have had heatsinks anyway. ensure proper wiring in the connectors. 
 

[BrianW]

I have a 337 for my glareshield with LED light strip controlled by a PWM dimmer.

But my incandescent lights still use the original rheostat-resistor-transistor for dimming control. I'd be happy if the original dimmer worked as it did when new, but it's 47 years old and I'm sure they are almost worn out. My M20J seems to be in a grey area. My dimmer uses the 200-ohm resistor although the drawing indicates it should be the later 50-ohm design. That's why I want to confirm that my installed rheo-resistor is paired with the proper transistor, but it wouldn't surprise me if they mismatched the components.

I will look under the glareshield the next time I get to the hanger to search and confirm the transistor and its location.

I never heard about PWM dimmers creating radio noise, but my King radios seem noisy, and maybe the PWM is contributing to the noise. I will keep that in mind the next time I fly. But less radio noise would also be a good reason to maintain the original dimmer setup.

I found out that Mooney produced a Mooney Transistor Mod Kit 919003-907 to change the transistor from the RCA 2N2016 to the Delco 2N3079 involving rewiring the rheostat and changing the resistor and replacing the RCA with the Delco transistor.

The best that my research could find is this partially obscured instruction sheet and a picture of the parts included in the kit (see attached). Unfortunately, I can see it is a 3-page instruction, but I only have this image of page 1.

Is there a resource where we could find the complete 3-page instruction sheets for the Mod Kit 919003-907?

I am hoping that if I have the RCA 2N2016 transistors that I can test them to ensure they are still working as intended. Otherwise, I may need to source new-old-stock for the 2N2016. And if the 2N2016 is out then I'd have to look at upgrading.

Did Mooney ever specify a silicone-based replacement transistor?

 

 

[Justin Schmidt]

10 hours ago, BrianW said:

I have a 337 for my glareshield with LED light strip controlled by a PWM dimmer.

But my incandescent lights still use the original rheostat-resistor-transistor for dimming control. I'd be happy if the original dimmer worked as it did when new, but it's 47 years old and I'm sure they are almost worn out. My M20J seems to be in a grey area. My dimmer uses the 200-ohm resistor although the drawing indicates it should be the later 50-ohm design. That's why I want to confirm that my installed rheo-resistor is paired with the proper transistor, but it wouldn't surprise me if they mismatched the components.

I will look under the glareshield the next time I get to the hanger to search and confirm the transistor and its location.

I never heard about PWM dimmers creating radio noise, but my King radios seem noisy, and maybe the PWM is contributing to the noise. I will keep that in mind the next time I fly. But less radio noise would also be a good reason to maintain the original dimmer setup.

I found out that Mooney produced a Mooney Transistor Mod Kit 919003-907 to change the transistor from the RCA 2N2016 to the Delco 2N3079 involving rewiring the rheostat and changing the resistor and replacing the RCA with the Delco transistor.

The best that my research could find is this partially obscured instruction sheet and a picture of the parts included in the kit (see attached). Unfortunately, I can see it is a 3-page instruction, but I only have this image of page 1.

Is there a resource where we could find the complete 3-page instruction sheets for the Mod Kit 919003-907?

I am hoping that if I have the RCA 2N2016 transistors that I can test them to ensure they are still working as intended. Otherwise, I may need to source new-old-stock for the 2N2016. And if the 2N2016 is out then I'd have to look at upgrading.

Did Mooney ever specify a silicone-based replacement transistor?

 

 

So that corrects the incorrect circuit. The delco is the silicon "near" equivalent.  Changes to a proper formed emitter follower with proper pull downs. The delco isn't manufactured anymore and the 3055 is a near equivalent.the resistor is easy to find at parts store like mouser or digikey, it is important to change that for the resistance,  proper pull down instead of original pull up, and the power dissipation. 

For the noise, first will need to isolate if it is pwm. Can disconnect it and see if anything improves. There are ways to limit it or eliminate with filters etc but question on what faa needs for that to remain non hanger fairy legal. Check the alternator filter too, those can fail and not filter out noise. A simple cap filter so as avionics added over years, more complex filters are needed but never added. Additionally,  if not grounded directly to chassis pwm,  switching power supplies from avionics, etc introduce noise, a high whine.

For my F I use every ounce of will power to not rip out all the wiring and do it proper

[MikeOH]

@BrianW

Both the 2N2016 and 2N3079 are silicon transistors.  The 2N2016 is an early, likely planar design (as opposed to an epitaxial design) and I suspect the designers took advantage of using the transistor in inverted mode; IOW, circuit A is NOT in error.  Using a planar transistor in inverted mode achieves a VERY low Vce(sat) which would reduce power dissipation when fully on.  Further, inverted mode increases the reverse breakdown voltage (i.e. Vec(max) > Vce(max) which would improve resistance to voltage spikes (which are destructive).

The 2N3055 was a very widely used part but I don't think it was available in a TO-36 case; TO-3 was typical. Mounting would need to be redesigned.  Further, I'd compare 2N3079 specifications carefully to the 2N3055 to confirm substitution suitability.

[BrianW]

Today I got back to the hangar. I removed to glareshield and started looking for the pair of transistors.

I was searching with a flashlight and inspection mirror.

They weren't behind the circuit breaker panel, not around the dimmer pots, couldn't see it within the console radio stack area, and not behind the pilot's panel.

I inspected around the teeny tiny copilot fuses (see photo) but I couldn't see transistors on the other side of those tiny fuses.

I suspect the transistors mat be the cause of dimming issues given my plane is almost 47 years old and we'll past the anticipated service life for the 2N2016, which is 10 to 30 years depending of service conditions.

I would've liked to know/verify if my plane had the 2N3079, as stated on the drawing for my serial number, or if it was the older RCA 2N2016 which pairs with the 200 ohm resistor on my actual dimmer switch.

I wish I KNEW where the pair of transistors were located to verify their part numbers.

I don't want to turn this into a bigger job by cutting Zip ties to physically follow the wires from my dimmer switch to the transistors.

[Justin Schmidt]

57 minutes ago, MikeOH said:

@BrianW

Both the 2N2016 and 2N3079 are silicon transistors.  The 2N2016 is an early, likely planar design (as opposed to an epitaxial design) and I suspect the designers took advantage of using the transistor in inverted mode; IOW, circuit A is NOT in error.  Using a planar transistor in inverted mode achieves a VERY low Vce(sat) which would reduce power dissipation when fully on.  Further, inverted mode increases the reverse breakdown voltage (i.e. Vec(max) > Vce(max) which would improve resistance to voltage spikes (which are destructive).

The 2N3055 was a very widely used part but I don't think it was available in a TO-36 case; TO-3 was typical. Mounting would need to be redesigned.  Further, I'd compare 2N3079 specifications carefully to the 2N3055 to confirm substitution suitability.

I can guarantee that the 2N2016 I pulled out of mine was indeed germanium. Back in the early days RCA and others manufactured them with Germanium , when silicon started becoming the thing then the same numbers were recycled for the silicon planar designs. epitaxial came later. Germanium is still used in some applications. silicon didn't pick up until mid 60s and planar design was about then. So it is almost guaranteed that mooney would have done a large buy of them being germanium. In many places large buys for a decade or more are done.

regardless of whether Mooney used the germanium or silicon or if parts got mixed, using inverted is still not proper for linear mode. analog dimmers do not operate in saturated mode and  there are issues trying to operate in the active/linear mode inverted such as beta collapse as it isn't linear, very poor transconductance (relationship between base voltage and collector current highly non-linear). So that means very little range which isn't linear at all (dimming is jerky and much of the Rheo isn't used still large power dissipation). So yes circuit A was not proper which is why they changed it a few times and eventually actually did do a proper emitter follower. As I said before, I do not know what designs came after in the later Mooneys. However, by that time they could have done an NPN driving a MOSFET which is a much better design and what all non pwm dimmers use.
But yes inverted modes are used a lot when in saturated mode(used as an actual switch)  

[Justin Schmidt]

9 minutes ago, BrianW said:

Today I got back to the hangar. I removed to glareshield and started looking for the pair of transistors.

I was searching with a flashlight and inspection mirror.

They weren't behind the circuit breaker panel, not around the dimmer pots, couldn't see it within the console radio stack area, and not behind the pilot's panel.

I inspected around the teeny tiny copilot fuses (see photo) but I couldn't see transistors on the other side of those tiny fuses.

I suspect the transistors mat be the cause of dimming issues given my plane is almost 47 years old and we'll past the anticipated service life for the 2N2016, which is 10 to 30 years depending of service conditions.

I would've liked to know/verify if my plane had the 2N3079, as stated on the drawing for my serial number, or if it was the older RCA 2N2016 which pairs with the 200 ohm resistor on my actual dimmer switch.

I wish I KNEW where the pair of transistors were located to verify their part numbers.

I don't want to turn this into a bigger job by cutting Zip ties to physically follow the wires from my dimmer switch to the transistors.

What is your serial number?
It would be difficult to think they wouldn't be either by the rheo or by those fuses, can you read wire numbers? At some point they actually created a box with the rheo and everything in it.
perhaps someone serviced it and either moved them or removed them. Does the rheo get insanely hot or bulbs burn out?

[MikeOH]

1 hour ago, Justin Schmidt said:

I can guarantee that the 2N2016 I pulled out of mine was indeed germanium. Back in the early days RCA and others manufactured them with Germanium , when silicon started becoming the thing then the same numbers were recycled

Below is the data sheet I found showing silicon; I'd be very interested to see one for a 2N2016 showing germanium.  I, personally, have NEVER seen a number reused for a different semiconductor base material (Ge to Si); process changes, sure...which have caused enough grief with substitution, but never replacing germanium with silicon.  I'm willing to learn; please provide a data sheet example.

2 hours ago, Justin Schmidt said:

using inverted is still not proper for linear mode

That's not always true. Lower noise and better efficiency was possible with some amplifier designs (linear mode) with inverted mode.  I agree, not the case anymore, and not applicable here as it's not an amp! And, while current gain is certainly lower, I don't think it matters too much for this application.  Mooney certainly improved the circuit over the years but I'm unwilling to believe the collector and emitter were swapped by mistake; I guess we'll have to agree to disagree on that