L-111 AO43-1 power resistor wattage?

[bassden]

Thanks for any help. I cannot read these power resistors since they are burned. Not this picture I stole this one on the internet I can see the ohms in manual however I do not see any indication on the schematic of the wattage values. Been some years since I replaced any resistors. Anyone know the specific wattage of R340 & R343 look identical in size. R341 looks like a 2 watt but could someone verify? Thank you for any help.

[tpappano]

IMHO, the small green ones are 5 watt wirewound, the 8200 ohm is a 2 watt carbon comp, the big green one is a 10 watt wirewound.

[bassden]

Thank you tpappano. That was my guess but I wanted to verify before ordering the resistors.

[tpappano]

You are welcome! Oh, and if you need to replace the 2 W carbon resistor, I suggest using a modern 2 watt "metal oxide film" (MOX) type. This type is what I use in 1, 2 or 3 watt applications. They will not burst into flame should there ever be an overload 8)

[Drawbar Dave]

I wonder what on earth caused them to burn up.

[tpappano]

Like "Dr. Phil" you are asking the "tough questions" 8)

[bassden]

The speaker was disconnected when I got the organ.

[Alek Z]

Bad power cord would be my guess, one time I had a bad power cord on an M3 and I was going to replace it but I figured for the time being it'd be fine. Nope. The wires started to touch and POP, then in the time it took the power overload to break the circuit, the synchronous motor started smoking, as did the amp. Synchronous motor was fine as was the amp, but the problems started to develop in the coming weeks and when I opened up the amp a couple wire wound resistors were fried.

[bassden]

When I was given the organ, the speaker connector was disconnected and they told me it did not work. At that time my best guess was that the connector was the only problem. It appears I have more than these resistors bad. I installed the new ones and they still smoke. I do have some audio though now as the tubes warm up but, I have to cut power. Looks like I will need to do some more troubleshooting. Going to look and see if anyone else had this problem here on the site. Thanks to all. Anyone had these problems before please tell me what you had done. Thanks again!

[tpappano]

The first suspect would be the power supply filter caps. Did R343 overheat? If so, there is a filter cap in the preamp chassis that could be the problem, and/or the ones in the main amp, too. If you have a multimeter, with the power off, measure the resistance from pin 2 of the 5U4 to chassis ground. This may provide a clue if one or more filters are failing shorted.

[bassden]

tpappano R343 did heat and turn a little color but the resistance is still good. I shut it off as soon as I saw any smoke. I checked the caps in that circuit and with just a resistance meter all 4 charge up after I depleted them. I need to get a capacitance meter. When you say, "the preamp" do you mean either or both the percussion or vibrato preamps? So many refer to preamps on so many posts and I want to assume but assuming will not be a good thing. There is a preamp stage in the main amp prior to the output tubes. Just want to make sure.

[tpappano]

All I have to look at is a schematic from an image search and similarly a picture of the organ's back side. It looks like there is a separate "preamp" chassis in the upper part of the organ where supposedly a filter cap is located. This one is "downstream" of R343, so if that cap (or something else) in the preamp chassis was drawing too much current, R343 (along with the resistors in front of it) could get hot. Once your ohmmeter reading stabilized, how many ohms did it indicate? From a quick glance of the schematic, it looked like you should read maybe 20,000 ohms. Some here have mentioned that a 5U4 rectifier can fail with a plate to cathode short, which would definitely cause excessive current through the resistors and capacitors in the power filter section. If you have one, you might try swapping it out. Also, if the locating key in the base of the tube is broken/missing and the tube is inserted with the wrong pins in the wrong holes, the same thing could happen.

[bassden]

On the meters' 20K scale I read 2.01. That is 2K ohms. I swapped out the 5U4 as well. Took a little longer for R343 to start smoking but it did and turned a little more discolored however good resistance still there. I pulled the percussion preamp which is the left side preamp and noticed there was a 12AX7 in the place of a 12AU7 and fixed that. On the other right side preamp it designates on the preamp for a 7247 tube which is a 12DW7. There is no writing on that tube to tell what it is so I will buy another. All the tubes test good at the moment with a tube checker. Have any ideas?

[tpappano]

I think 2k is way too low for a reading from 5U4 pin 2 to ground. I see that there is yet *another* separate chassis, the vibrato amp, which also has filter caps on board. Both the vibrato amp and preamp appear to have power connectors that can be unplugged. Try unplugging these connectors then repeat the 5U4 resistance check and see if the fault clears. If the resistance jumps up, plug one connector at a time back in to see which one(s) is/are causing the problem. If the resistance does *not* jump higher, you may have bad caps on the main amp too. Fun stuff 8)

[bassden]

I will check as you have described. Thank you again for the help. I am getting more acclimated to this model because I understand where you are headed.