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 Post subject: Re: RME 69
PostPosted: Jan Tue 09, 2018 8:38 pm 
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Location: hillsborough, nc
It's a tunable RF amp that helps almost all receivers. The cheaper the receiver the more help!
WL


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 Post subject: Re: RME 69
PostPosted: Jan Tue 09, 2018 8:42 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1690
Location: Eagan, Minnesota, USA
Rodger,

Regarding the line bypass capacitors and placement, my power transformer has the wires coming out of the transformer from the side of it. They go underneath the chassis from there. So, am I ok that there are no capacitors hidden somewhere within the transformer? I want to install the newly painted bells, and would like to make sure I didn't miss something.

Also, I'll need to replace the power line cord. Probably go with a new 3 wire line cord from AES. RME did some kind of wrap with tape to the original line cord. Any thoughts on a decent way to install the new cord and possibly a fuse? Looks like there is enough room there but no mounting holes to set up a terminal strip. I'm going to avoid any drilling on this chassis. I'm wondering how other people have handled this.

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 Post subject: Re: RME 69
PostPosted: Jan Tue 09, 2018 8:55 pm 
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Chris,

Glad to help feed your addiction :)

Edebris has the various model preselector manuals available here: http://bama.edebris.com/manuals/rme/

These can really perk up an older and/or simpler receiver. I paired a DB-20 with my Hammarlund Comet Pro when I was using it for a vintage event a couple of years ago and on 20 meters it made a huge difference.

Although not old vintage, a vintage accessory no vintage receiver enthusiast should be without is an Autek QF-1A. It is at its best for CW however it is also very useful for AM and SSB in reducing broadband noise and/or tailoring the audio for better intelligibility. The notch filter is wonderful for removing AM hetrodyne interference to make that operation much more enjoyable. It also allows modern low impedance phones to work well with older receivers since the QF-1A has a high input impedance and won't load down the high impedance source presented by many vintage receivers. Couple that with a pair of comfortable headphones with a built in volume control (used to provide a little attenuation which will remove the hum often experienced when using modern high efficiency headphones with vintage receivers).

Like the preselector the increase in performance is greater with lesser receivers but I first used the Autek QF-1 with a fully filter equipped late production R-4C in my contest setup and it was very useful there. These are often found at hamfests and similar units were made by other companies but I like the Autek setup best and still prefer it to external DSP boxes in that it can provide a real improvement without imparting a horribly processed sound. Manual is here for those curious: http://hammadeparts.jivetones.com/Amate ... manual.pdf

The only vintage receivers the QF-1A won't work with are some of the early sets that put the headphones directly in series with DC coupling between the B+ and audio tube plate. It won't hurt the QF-1A because the input is protected by coupling caps but the input plug will short receiver B+ to ground so you will have to use an audio transformer with a set like that (which is a great idea anyway since wearing a vintage set of headphones with full B+ through them is not a great safety idea).

Frank, I will end my thread hijack here but I think threads like what you started bring a lot of people into vintage receivers and some will grow disillusioned with the performance and fade away if they don't realize how practical these receivers still are today with just a little help from some supporting accessories like preselectors and audio filters.

Rodger WQ9E


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 Post subject: Re: RME 69
PostPosted: Jan Tue 09, 2018 9:05 pm 
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Frank,

You are safe with the transformer not having the line bypass caps in it. For the most part I think the capacitors mounted under the cover was more of a RME-45 era thing but I repaired one RME-69 that had that style transformer and I suspect it came through factory service of a receiver with a bad power transformer.

For three wire power cord installation, and I do that to almost every piece of gear that crosses my bench, I find that usually the existing cord hole can be used. Depending upon its size and the diameter of the replacement cord you may be able to use a more modern two part "squeeze" type holder but if the hole is too small to accept one of these I use a grommet that is a tight fit to the new cord. If you have a situation where the proper grommet for the hole doesn't provide a tight enough fit for the cord (probably won't be the case with the 69) use the closest interference fit you can put in the hole and then install a tight fitting grommet around the cord from the receiver inside so that it prevents the cord from being pulled out of the cabinet.

For fuses I use an inline holder to avoid drilling any holes and with a properly sized fuse it isn't going to nuisance blow so if the fuse opens you need to go into the receiver anyway and not having an external fuse isn't really an issue. Follow modern electrical code so that the fuse and switch are both in the hot/load side (should be the black wire for U.S. cord sets) and I put the bypass cap on the protected side of the fuse. The neutral side should never be switched or fused and usually goes directly to one transformer terminal. Be sure and use modern line rated bypass caps.

I cut the load and neutral wires a little long so there is some slack in them but I keep the ground wire short so if someone does pull on the cord it will take the strain. This is one wire that I do make mechanically secure before soldering and make sure it goes to a solid mechanical and electrical ground point.

In cases where you need a terminal strip and you don't want to drill holes you may find you can mount it using an existing tube socket or transformer mounting point OR you can often solder the terminal strip ground lug to an existing soldered chassis ground point which will also provide the mechanical support for the strip.

Rodger WQ9E


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 Post subject: Re: RME 69
PostPosted: Jan Tue 09, 2018 9:24 pm 
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Location: Eagan, Minnesota, USA
Rodger,
Thanks for the ideas on the line cord/fuse installation. I might be able to solder a new terminal strip to that chassis, and it probably will be the best way to solve the mount issue. There are so many places on the chassis that RME soldered directly to for grounds that one more won't matter!

You're not hijacking this thread. Please keep the additional information coming. It's interesting, and I'm learning as I read. The goal for me is to learn and have fun. Thanks again!

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Frank
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 Post subject: Re: RME 69
PostPosted: Jan Tue 09, 2018 10:43 pm 
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Frank,

You are welcome!

One other possibility is you can often find an unused pin on a tube socket when you need a tie point. This isn't my first choice for a couple of reasons but it can be a good option when you need one or two new terminal points and the manufacturers also often made use of this. But you need to be careful of a couple of things:

1. Check the tube data book carefully to make sure that there isn't an internal tube connection to the blank terminal paying special attention when there were glass and metal versions of the tube because sometimes pins blank on one version will be present on the other. You also have to be careful when using substitute tubes when this is done to make sure that the otherwise acceptable sub doesn't utilize the unused pin that is blank on the original type. This isn't a huge deal and equipment manufacturers used blank pins as tie points frequently.

2. When dealing with AC line power be careful that when choosing a tube socket tie point that it doesn't bring the AC wiring where it will couple into a low level high impedance line running nearby (like the BFO feed to a detector or a low level audio line) or you will induce hum into the receiver.

It is also useful to remember in some of the later RME gear that they used a lot of loctal tubes and in my experience these sockets are the most prone to contact issues of any of the major tube styles. Fortunately most receivers using these tubes have several unused socket pins and they are easy to move to where they are needed.

I have run into very few problems with miniature tube socket contacts that couldn't be cleared by cleaning and I don't remember ever having to replace an octal socket contact except where someone had broken off the terminal trying to remove components but I have done a lot of loctal socket terminal transplants due to the inability to establish a reliable contact. The RME-99 receiver promoted the use of these tube types as having superior base insulation for better high frequency performance and they were used in a number of sets in addition to the auto receivers where a locking type base was actually needed. These types can stick in place because in normal use they are held securely and the tube locator/locking pin often adheres to the mating lock on the socket over time making them extremely difficult to remove and it is very possible to cut yourself by breaking one of these trying to remove it. If it doesn't come out easily use a tube puller or other safe device to protect your hands and if it is really stubborn use a wooden dowel or similar item with a light mallet to tap the tube loose from below by lightly tapping the locator pin. In extreme cases you will need to use penetrating oil on the locking tab to prevent tube breakage but this is very rare.

Rodger WQ9E


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 Post subject: Re: RME 69
PostPosted: Jan Fri 12, 2018 5:25 pm 
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Location: Eagan, Minnesota, USA
Time to work on the electrolytic capacitors. The original 3-section can is still installed. What I need to know is where do these leads from this capacitor connect to? I want to take it out of the circuit, but I cannot see where the wires come out from it to follow them to their connecting points. I need to know what these connecting points are to get that old part out of the circuit.

Next is placement of the three new capacitors. What I think I can do is connect each new one to each of the terminals that are on the transformer side of the chassis. From the front of the panel working downward, what I think the order of the capacitors are is: C34, C35, then C23. They are 8 mfd, 8mfd, and 12 mfd.

Any help on this would be appreciated!

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 Post subject: Re: RME 69
PostPosted: Jan Fri 12, 2018 7:40 pm 
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Frank,

Electrically one of the 8uf sections goes to the cathode of the rectifier/input side of choke 1 and the other 8uf section goes to the output side of choke 2. The 12uf section connects at the junction of chokes 1 and 2. Physically there are a lot of places where these capacitor leads can be connected to the circuit, especially in the case of the output capacitor and there is no guarantee that every RME-69 was wired exactly the same way since lead layout at DC is not critical. Although it sounds somewhat tedious the only sure way is to follow each of the three leads from the existing capacitor block to its termination point; based upon the termination point it will be easy to tell whether it is the 8 or 12 uf section. The input section in most sets will be hooked directly to a rectifier cathode lug along with the wire from the choke so it should be easy to identify. The center section of the CLCLC filter should also be easy to locate since you can trace it via the leads of chokes 1 and 2. The only one that might be somewhat difficult to find is the output capacitor lead but the RME-69 is still a pretty old and reasonably simple set so lead tracing isn't too bad.

However, rather than disconnect the leads at the circuit connection points you may want to disconnect the leads where they come out of the old capacitor because I expect given the layout of the 69 you will be able to mount the new capacitors as a group under the chassis section that sits under the transformer and choke 1 area placing the capacitors somewhere near choke 2. I suspect that the free leads from the old capacitor can be rerouted to the new capacitor location keeping the wiring style fairly close to original. Putting all three of these filter caps in this section also avoids possibly placing one and its ground near a sensitive portion of the circuit potentially causing hum issues.

Maybe someone has their RME-69 open and can provide more guidance but I don't have any good photos of the underside of either of my 69 receivers. And right now I am waiting for the wind to drop off so I can go try out my new Canon EOS 1DX Mark ii camera that arrived this morning so I will be taking a couple of days off from vintage gear to get used to operating the upgrade from my 12 year old EOS 1 digital and a lot has changed in 12 years.

Rodger WQ9E


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 Post subject: Re: RME 69
PostPosted: Jan Fri 12, 2018 8:00 pm 
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Location: Eagan, Minnesota, USA
This would be very simple to figure out if you could only see the leads coming out from the can of the original capacitor. You could then locate each of the three wires and then cut them out of the circuit. But the way this set is built, you cannot see any of the wires because of the way the coil section is built. It is right over the area where the wires would exit the can. Then there is also a flat piece of metal that I think covers the opening where the wires exit the can through the chassis. And this piece of metal can barely be seen. I can see one wire exit this flat metal cover, and it goes to one of the terminal strips on the transformer side of the chassis. If this is in fact a lead from the old capacitor can, then one of three is solved. But I can't see or reach any other part of that flat metal cover. I guess I'm going to have to try again over the weekend and hopefully I can get a break on this somewhere. I suspect that there are more than a few RME 69's out there with new electrolytic capacitors installed and the old ones still in the circuit. Never seen anything like this and I've done a few sets over the years!

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 Post subject: Re: RME 69
PostPosted: Jan Tue 16, 2018 7:22 pm 
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Location: Eagan, Minnesota, USA
I had a three day weekend, and with the weather as harsh as it's been, conditions were excellent regarding undisturbed bench time. I started Friday night after work, worked most of the day on Saturday and Sunday, and wrapped up the rebuilding process yesterday afternoon. All of the wax capacitors have been replaced. RME used .01 mfd and .1 mfd for the paper caps. I replaced a few of the mica capacitors, especially when the terminal they were connected to required a lot of disturbing to remove old parts. Just being proactive. They used a lot of 250 pf mica caps in this set. The resistors were unbelievably out of spec. I had many 50K that read over 75K. Many 100K read almost double. I replaced almost all of those 1/2 watt dog bone types with new ones ( either 1 or 2 watt).

The electrolytic capacitors required some physical wire tracing to find out where they connect to. One of the three section electrolytic connects to one of the three separate terminals that are used to install the new electrolytics. The other two leads connect in the general area of the 42 tube socket. One goes to that socket. I don't remember exactly where the third one connected. I performed continuity checks with the three terminals mentioned before to the connecting points on the chassis for the two remaining leads to verify what I had was correct. The fourth electrolytic easily is replaced by installing it to the bleeder resistor terminal and to ground. That takes care of the electrolytic capacitors.

I removed the volume control/mute shaft and the associated bracket and switch to gain access to the area for parts replacement. While I had it all apart, I removed the volume control and took the cover off of it and applied some DeOxit for cleaning. Now that control is smooth, and quiet in operation. Reassembly took a little time to adjust everything so that the shaft and control operate smoothly.

I marked the schematic as I went along, and verified that the schematic matched my radio. So I know the version to refer to should future repairs be necessary.

The tubes tested good on my TV/7, so they were installed. With the rebuilding done, I could now bring it up on the variac.
The set came to life with no issues. All of the controls are quiet, with the exception of the band switch with it's normal static between bands as you switch. I have not cleaned it with DeOxit yet, but will get that done soon. Every other control is quiet and works properly. The accuracy of the dial is almost perfect, even after all of the parts changed. And that could be due to removal and replacement of the dial indicators. The set is a very good performer. I could copy SSB using the BFO method, and it would remain on frequency. Short wave and broadcast band DX is a pleasure on this radio. The strong local stations do not overload it either. It is an excellent all around performer from what I can see so far. I have about 6 hours run time on it now, and will run it every night this week after work.

I like this radio very much. It's refreshing to have simple controls and a simple dial to work with. It's all business and seems to get the job done.

I have not performed an alignment yet, and that will wait for a while. I still have to replace the power cord on it too.
Next will be the pre-selector rebuild. Maybe in a few weeks.

I had a lot of fun working on this set over the past few days. I was not in a rush, had all day for as long as I wanted, and took breaks between steps. It all worked out very well.

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Frank
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 Post subject: Re: RME 69
PostPosted: Jan Tue 23, 2018 5:53 pm 
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Location: Eagan, Minnesota, USA
I've been playing this set just about every day, and noticed an occasional noise that reminded me of the way a Philco 690 sounds when the candohm is going bad. So I decided to check this out. What I found was a broken soldering joint at the switch to mute the radio. What I think happened is, when I took the switch bracket out to get at the parts below it, I had to bend that switch out of the way. There is a section of bus wire that is soldered to that switch and runs to the multi-section resistor next to it. It was that piece of bus wire that loosened enough during this movement, but looked like it was perfectly connected with no indication that it broke free. I decided to replace that bus wire with new, and do the entire run over. It's now perfectly quiet and no more 'where's that noise coming from' happening. What a great feeling to solve that problem!

I'm now going through the speaker that mates with the radio. I took it all apart, and cleaned everything up. The cabinet had a few places where the paint looked faded and some small marks. I have an automotive lacquer that matches perfectly. I laid down one coat over the entire speaker cabinet. The wrinkle finish from the factory is in good shape, so this top coat refreshed the look of it. I'm going to replace the wiring with black AC line cord. The wire on it now is brown line cord. It may be original due to the way the wire is knotted in the plug. Looks like a factory install. I don't know why they would use a brown cord when the cabinets are black. But it was the depression when it was made, and they probably got a deal on this wire. Or, maybe it was changed at some point. Who knows.

So soon this speaker cabinet project will be wrapped up. Then I'm going to go through the checks for voltage and resistance per what's in the manual. Then possibly touch up the alignment. Later on, I'll get to the pre-selector. But that will be awhile.

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Frank
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 Post subject: Re: RME 69
PostPosted: Jan Fri 26, 2018 5:16 pm 
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Location: Eagan, Minnesota, USA
I'm planning on replacing the line cord this weekend. I have a new three wire cord from AES to install. The set did not come with any line bypass capacitors. Should I install one from the black/switched lead to ground? Is there a benefit to doing this or could this create a problem?

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 Post subject: Re: RME 69
PostPosted: Jan Fri 26, 2018 5:35 pm 
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Most vintage electronic gear had line bypass caps and they do serve a useful purpose in reducing undesired signal ingress and egress from gear and can also help limit SOME of the transient spikes on the line. Best practice is to use these caps from both the load and neutral to ground since although neutral will be at ground reference at some point (either the main panel or at the power company transformer) it has very high inductance at RF and thus high reactive impedance so there will be noise on both the neutral and load sides of the line. I put the load side capacitor after the fuse and power switch so that it isn't constantly exposed to voltage even with the set off; this isn't as important with modern line rated caps that are designed to withstand typical line surges and fail safely without fire if their limits are exceeded but it is still best practice.

I wouldn't go any higher than .01 or you may starting running into GFI issues. And if the set isn't grounded properly (which it ALWAYS should be) you create an ever growing shock hazard with larger values of capacitors. Some of the military gear was known for abnormally large bypass values.

For bypass capacitors to be most effective the set must have a good RF ground and the grounded wire at the outlet has the same issue as the neutral in that it is long and has high impedance at RF so although it does its safety job for DC and line frequency AC it is often worthless as a RF ground. Even so bypassing both sides of the line to the common ground point in the chassis is somewhat useful but it isn't optimal unless the set is well grounded for DC/low frequency AC AND RF.

Rodger WQ9E


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 Post subject: Re: RME 69
PostPosted: Jan Fri 26, 2018 5:57 pm 
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Location: Eagan, Minnesota, USA
Rodger, thanks for the reply! I will add one cap on the black and one on the white AC line connection as you've described above. What I think I'm going to do is attach a terminal strip to one of the screws that attaches the choke to the side of the chassis. I'll connect the wires there. I'll make sure the ground terminal gets the green wire, and also run a bus wire to a good chassis connect point for a firm ground. The black wire cap will go after the switch to keep it from constantly being active with line voltage.

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 Post subject: Re: RME 69
PostPosted: Feb Tue 06, 2018 9:36 pm 
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Location: Eagan, Minnesota, USA
Installed the new 3-wire line cord this weekend, and added an AC line capacitor on each of the black and white line leads to ground. Also had the 6B7 tube develop intermittent noise. It probably was an original tube to the radio, as it was an etched base Sylvania, and would be appropriate for the years those sets were built. Replaced it with a NOS 6B7, and no more noise issues.

I think I'm down to the final task, and that would be performing an alignment. I'm not sure of a few things though. One thing I'm wondering about is whether the alignment should be performed with the chassis installed in the cabinet. There are access holes on the bottom of the cabinet. But it's always easier to perform an alignment with the set out of the cabinet and on the bench. Is this a concern or not?

The instructions for alignment are different from what I'm used to seeing. For one, it is not recommended to use an RF generator to perform the I.F. alignment. They advise using a station around 700KC, then tuning past it going upward about 15KC, then bring it back by using the band spread dial, supposedly for accuracy. You also have to set up the crystal filter a certain way that I'm trying to figure out. My set is number 1449, so it might be an early one. I don't think it has the later changes that RME added to the later sets. So I'm trying to get an understanding about this whole I.F. alignment procedure.

Then, it's somewhat confusing about how to perform the R.F. alignment for each band. The Electric Radio article I've referred to sums up the RF alignment by saying that you first set the signal generator for a frequency, and make an adjustment. Then the next step gets confusing. It says to then move to a higher frequency, also set the signal generator to that frequency, and then move the band spread knob from '180' (minimum capacity) backwards until the signal comes in. Then it doesn't say what, if anything you do at this point. Sounds like you just tune it in and do nothing else. That makes no sense to me.

So, any thoughts on the alignment procedure would be appreciated. Hopefully I can get to this either this weekend or next.

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 Post subject: Re: RME 69
PostPosted: Feb Mon 12, 2018 6:08 pm 
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Location: Eagan, Minnesota, USA
Went ahead with the alignment this weekend. I installed it in it's cabinet, then performed the alignment using the service notes for the RME-69, and also referred to the Electric Radio article as well.

I used a 700KC signal when I did the I.F. stages, and I followed the instructions to the letter as printed in the service manual. It is a different procedure from what I normally find, but it is what is called for to get the I.F. stages in line with the crystal selector. It wasn't as complicated as I thought it might be, and went well.

Next, I performed the RF alignment. Band one has two adjustments. One at the low end, and the other at the higher end. Nothing unusual there. Bands 2 thru 6 have one RF adjustment that is to be done at a specific frequency. Band 5 and 6 also have a peaking adjustment in addition to the RF adjustment.

I took my time, and it all went very well. The radio is now completed, and the next phase will be rebuilding the DB-20 pre selector.

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 Post subject: Re: RME 69 / DB-20
PostPosted: Feb Fri 23, 2018 8:32 pm 
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Location: Eagan, Minnesota, USA
I'm starting to work on the DB-20 pre-selector now. I now have the chassis out of the cabinet and have started cleanup tasks. The cabinet cleaned up like new. It will not need any touch up work. On the top of the front of the panel, it looks like there were stickers that said DB-20. They fell off, and there is some glue faintly visible if you look the right way. It won't come off, but is so subtle that it's not worth any concern. I do wonder if RME would have placed them there or they were added by the owner.

It looks like there is a production change on this unit where the switch to go from pre-selector to simply antenna has been moved to a place right above the left most control. The units I've seen on the web have three small controls and a tuning knob. So this unit has four small controls and tuning knob. They are antenna switch, on-off switch, sensitivity control, band switch, and tuning. The change looks to be factory judging from the parts used, wiring, and the way the work was performed.
I'm going to further search to see if this was a late production or why it is different.

Nothing has been done to this unit, so I'm starting from a good place. Hopefully will have time over this weekend to work on this.

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