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I need a new speaker for a UP SD90 proto 2 engine #20-2368-1. Speaker is not clear sounding any longer. I will order a similar volume pot in case that is the issue but the speaker had particles on the magnet besides on the cone. I cleaned that off, still not sounding good.

The exact replacement is out of stock which is a 16 ohm, 5 watt, 45mm speaker. There are other 45mm speakers in stock and are as follows: 4 ohm, 3 watt and 16 ohm, .7 watt speakers. Can I use any of those types or wait till it is available through MTH? Or is there another supplier I might try for the exact replacement.

Thank you,


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The trick is to match the impedance load and wattage requirement. This can be achieved using a lower resistance speaker in series with an additional load -- i.e., the 4-ohm speaker with an additional 12-ohm resistor load. The additional load can be more speakers in series if you have room.

In my other smaller hobby (tweaking my truck), I decided to replace my lighting with LED's. They sell resistor kits to prevent the turn signal LEDs from flashing too quickly and I believe they're 6-ohm and two could work in series with the speaker to give you a sufficient load. I'll check my parts stash and see if I have some (I went with some bulbs that have built-in resistors and cooling fans instead of using the resistors).

Ted, I think someone gave you some wrong information. I looked at my SD90 that was originally proto 1 and converted it to proto 3. The speaker housing is for the standard 50mm speaker. MTH BF-0000033 which is available from MTH. It is not the original type but more of a pancake speaker, just won't be as loud. There  is a guy on the internet that sells speakers like the original type plus wiring harnesses. I forgot who it was, but maybe Gunrunner or GGG knows who  it is.


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The 16 ohm, 5 watt speaker in the engine came off MTH parts under the SD90 parts list. BF0000021. I put the part number you suggested, BF0000033 and came up as 16 ohm 3 watt 50mm for $18 and also listed another speaker, BF0000022 which is a 16 ohm 5 watt 50mm for $10 which would be the exact one I need.

I am no expert on electronics here, just want to order the correct one. I will be at York and maybe they might have some speakers with them.

Thank you.

Last edited by Ted Bertiger

Measure the diameter of the speaker in your engine to know.  The MTH parts picture show all the possible combos and sometime all the diesel part which do not necessarily apply.  I reported that when I did my review for MTH, but it is the way they are doing things.  It is not like a Lionel diagram that is the actual engine parts.  So you have to look at the part on your engine and match it to what is shown to ensure you order the correct part.  G


I removed the speaker and measured it and it is a 50mm speaker. I tried to clean whatever small pieces there were on it and moved the volume pot back and forth many times as that can clean the roller inside. Still get a crackling sound, the horn and bell are loud but you hear a crackling sound that goes along with the rev sounds.

Probably going to replace both pieces.


I have 3, like new.  I think two are MTH and one is Weaver.  The Weaver one has a smaller magnet.  You can take what you like.  I'll put them in my car now and bring them to York on Thursday.

I installed a speaker in my MTH GP38 and Weaver SD40 called a Tang Band.  I just used 2 sided tape to hold it in place, but man does it sound good.  I think it is 4 ohm however.  The MTH engine runs RailPro now so 4 ohm was suggested.



Tang Band Speaker  The 1925S fits in the MTH fuel tank - Start at 1:03.


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Last edited by Ron045

BF-0000021 is 45mm, not 50mm. MTH has been out of those for years, wonder where they found those at. Is that what they are calling it now, BF-0000022? There wasn't a BF-22 before.

I just searched parts and found the 50mm 16 ohm speaker,   I believe it used to be the BF-0000033, that's the only 16 ohm 50mm speaker listed on the common parts list from 2016.

I plugged in the BF0000022 part number and it is a 16 ohm 5 watt speaker for $10 on MTH parts site.

Ron, not sure if I should use a speaker with lower watt ratings. I will look at them at York and see from there.

Gunrunnerjohn, what did you say? Stop using it! Lol! I got your message my friend. You are one of the electronics experts here.  See you at York.


Sorry if I was not clear.  Those three speakers in the picture are 16 ohm, 50mm speakers   The new Tang Band is 4 ohm.


Here is a picture of 2 Starr speakers. Both with the same problem. These are the 45mm smaller speakers, but the larger ones have the same problem of the plating flaking off and glue seeping out.. The taller one is BF-0000021 at 5 watts and the replacement BF-0000031 at 2 watts. Both are brand new and un-useable. I guess I will order the BF-22 and see what they send.IMG_0859


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Chuck, Don't waste your money it is the 50mm.  They still have the BF-33 but it is an Ashi and different form.  I bet those starr's are old stock put back in service.

Starr's are the bad version and i have seen 4 ohm and 16 ohm starr's disintegrate.  If an engine has one that has not, I bet it was replaced at some point so it just has not started to disintegrate yet.  This goes all the way back to Strock as SM with the notices to stop using them.

Now the whole short the coil issue to blow audio amp, I have not seen.  I have replaced plenty of  heavily damaged speakers with board audio still fine.  The coil is isolated from the magnet.  I know this because I had a speaker where the magnet came off the frame. Can a speaker short... sure.  The shorted speakers I have seen looked perfect, but blowing whistle usually would shut the board down.  Usually it is the coil wire lead going to the solder pad though.  Runs too close to the frame and vibrates into the frame when generating sounds and ultimately damages coating and shorts.  G

not to hijack this thread,but I have a proto2 consolidation steam engine. the sound set is nice,but the factory speaker makes it sound like crap. the speaker is fine btw. is there a better sounding speaker I can swap for the factory one.

l have not opened the tender to see how much room there is for a different one. I suspect the speaker is under the board so maybe I am asking to much to find a better one.

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