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Thought I’d share these Senco sound tenders that I’ve acquired over the past year or so. These were an early attempt at a sound system from 1947, and worked by connecting a record player to a box that was hooked up to the track and playing the sound through a speaker on board the tender. I don’t have the box, unfortunately, so I don’t have any way of hooking it up to work.

I have three of these tenders, but only one has the electronics inside of it - here's a photo of the three, plus a frame and some other parts.

Here's the underside of the one with its electronics - the speaker is clearly visible through the slats on the bottom.

Here's a closeup of one of the three rail Auel Industries trucks these ride on. Three rail Auel trucks with the electrical pickups are fairly rare, but found on all of these. The flanges are the most obvious difference between the two and three rail versions, but the three rail versions also have simplified bolsters and spring planks, and only have 2 springs on either side versus 3.

These tenders are fairly nice, but they don't fit well with anything. They are far too wide to look good with postwar Lionel, which is probably what they were intended to go with, and they are not detailed enough to fit well with scale models of the time. They're also very short, so only fit with small locomotives.

Here's one of the dummy couplers that these come with - probably the ugliest I've ever seen, with the oddly tapered shanks and rough cast look to them. No idea who made these, maybe Senco.

I have three records for these - one is labeled "297" and two are labeled "299"

On the one labeled 297, the A side is labeled "PENNSYLVANIA RAILROAD --- CALL ON THE FLAG LEAVING CRESTLINE." The B side is "AT UNION STATION PENNSYLVANIA'S BROADWAY LIMITED"

On the ones labeled 299, the A side is "PENNSYLVANIA RAILROAD SHORT RUNS STATION TO STATION . . NO ANNOUNCEMENTS . . . TWO COMPLETE RUNS." The B side is "PENNSYLVANIA RAILROAD --- LONG RUN WITH A WHISTLE CONFIRMING A STOP AT THE NEXT STATION."

And here's the instructions on how to set them up, expecting you to modify your record player:

I'd be interested in getting the mixer box that goes with these - it would be really neat to get one of these working.

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Original Post

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Above:

"These tenders are fairly nice, but they don't fit well with anything. They are far too wide to look good with postwar Lionel, which is probably what they were intended to go with, and they are not detailed enough to fit well with scale models of the time. They're also very short, so only fit with small locomotives."

Oh, I don't know. This Senco tender works well behind my modified/re-lettered Williams Ten-Wheeler (a nominally scale 4-6-0). The AT&N RR was real and had similar 4-6-0's. The USRA tender that came with the Wms loco was too big. My Senco tender (eBay) came empty.

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The tender has an ERR DC Commander (no cruise required with this engine's good gearing) and a frame-mounted Electrocoupler and a little added detail; I added the tool boxes partly to hide the roller pickup I mounted for better continuity.

Original trucks; the tender body is insulated from the frame for TMCC antenna mounting. Front steps, tool boxes, basic handrails added. Nice-looking, small scale-sized tender, suitable for all sorts of projects. Truck flanges are Hi-Rail compatible.

Ironically, as it is a "sound tender", I did not add Railsounds.

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Last edited by D500

Guess I'll post my Senco tender as well.  It was donated to me by a forum member (thanks again @Dave Funk). I think it looks right at home behind my semi-custom 2-8-0 whatever loco that I rebuilt.

There's a whole part of the thread dedicated to the teardown and rebuild of the Senco tender here.

Here's the final product:

Those LP's are cool!  When Dave sent me the tender, he explained how it worked.  I gutted mine in favor of a PS1 board and sound, but I kept the guts in case I ever want to rebuild again as original.  Still have the original battery and oval speaker!

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Last edited by Jeff_the_Coaster_Guy

I happen to have a Senco sound tender set that is mint in the box and has all the paperwork and the elusive mixer box. I bought this from a friend in TTOS whom I did part time Ebay listing work for. He had acquired a collection of vintage 2 rail O scale. Most of it was from the 1940s and 50s. This collection had a bunch of Senco sound tenders, mostly 2 rail models but there were some 3 rail as well. There were 3-4 2 rail models that were mint in the box and a couple mint 3 rail models. There were also a bunch of 2 and 3 rail loose tenders as well. I’m guessing the collector must have bought a store’s remaining inventory back in the 40s.

This is the only time I’ve ever seen boxed examples of these. I have pdf scans of the paperwork for those who are interested.

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@Johnbeere posted:

These tenders are fairly nice, but they don't fit well with anything. They are far too wide to look good with postwar Lionel, which is probably what they were intended to go with, and they are not detailed enough to fit well with scale models of the time. They're also very short, so only fit with small locomotives.

Scale modelers of the time would be used to detailing such things themselves, and, frankly, the detail level of most scale equipment was not much higher than that of the 3-rail.

I happen to have a Senco sound tender set that is mint in the box and has all the paperwork and the elusive mixer box.

I have pdf scans of the paperwork for those who are interested.

Cool! I'd be interested in seeing the paperwork - all I have is the one instruction sheet that I showed in my original post. Have you ever tried setting it all up and seeing what it sounds like? I'd be interested to hear the sound quality out of it.

I didn't realize that they also made these in 2 rail, do you still have any photos of the underside of those?

Since my original post, I've gotten ahold of a mixer box, but it's a big mess. All the screws are stripped out, it's missing wiring, and it's filthy inside. Do you think you could post photos of the insides of your mixer box so I can see how it should be?

@palallin posted:

Scale modelers of the time would be used to detailing such things themselves.

Definitely. It just seems odd to me that Senco would choose a scale width for a three rail tender in 1947. There were very few scale-sized three rail engines produced back then, so there wasn't too much to pair it with.

@Johnbeere posted:

Cool! I'd be interested in seeing the paperwork - all I have is the one instruction sheet that I showed in my original post. Have you ever tried setting it all up and seeing what it sounds like? I'd be interested to hear the sound quality out of it.

I didn't realize that they also made these in 2 rail, do you still have any photos of the underside of those?

Since my original post, I've gotten ahold of a mixer box, but it's a big mess. All the screws are stripped out, it's missing wiring, and it's filthy inside. Do you think you could post photos of the insides of your mixer box so I can see how it should be?

Definitely. It just seems odd to me that Senco would choose a scale width for a three rail tender in 1947. There were very few scale-sized three rail engines produced back then, so there wasn't too much to pair it with.

I can send you scans of the pdf’s when I get home tomorrow or on monday. One of the sheets is a product guide. I did try setting mine up with my turntable. I get a hum from the tender speaker but the sound doesn’t transmit. I’m thinking the old condenser packs are bad in either the tender or the mixer box: they are over 70 years old afterall. Recreating the circuits with modern components would probably be necessary.

The record is 45 rpm and sounds pretty good. The recordings are very similar to railrod audio records that were commonly sold in the 60s and 70s. Stationary microphone that recorded a locomotive runby or a station arrival/departure.

I did open my mixer box up to look inside. All the components are wrapped up in some type of insulating fabric. It would be a pretty invasive operation to get it out to see the whole circuit. I’m not sure yet how deep I want to probe into it yet.

I don’t have photo’s of the 2 rail models since ot was over 10 years agothat these went up for sale. I recall they look the same as the 3 rail models but no center rail slider and insulated wheel sets.

Thank you to all who have posted information about the SENCO sound tender.  After I found and purchased the tender from eBay, I found this info in the forum.  Knowing nothing of the tender prior to finding the forum, my interest has really peaked   I plan to mate my recently purchased tender with a tenderless American Flyer prewar O GA 0-6-0 switcher. 

Tried searching but could not find a description of how the sound worked.  From what I could gather, the phonograph signal is mixed with 60 Hz (or DC) track voltage.  And from what I can see the tender had not much more than a speaker in terms of electrical components.  So given the technology of the period, I'm thinking the tender speaker is simply playing the 60 Hz track voltage along with the higher frequency audio from the phonograph.  And the speaker did not have sufficient low-frequency response to the 60 Hz "hum."

From the instruction sheet posted earlier, it appears tubes (vacuum) were required perhaps to amplify the weak phonograph signal to a voltage level comparable to the 60 Hz track voltage?

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@stan2004 posted:

Tried searching but could not find a description of how the sound worked.  From what I could gather, the phonograph signal is mixed with 60 Hz (or DC) track voltage.  And from what I can see the tender had not much more than a speaker in terms of electrical components.  So given the technology of the period, I'm thinking the tender speaker is simply playing the 60 Hz track voltage along with the higher frequency audio from the phonograph.  And the speaker did not have sufficient low-frequency response to the 60 Hz "hum."

American Flyer superimposed the horn or whistle sound waveform on the track voltage and passed it to a loudspeaker on the train through a crude high-pass filter that rejected the 60-hertz power-line frequency.

HORN SERVICE KIT for American Flyer STEAM DIESEL ENGINES S Gauge Trains Parts | eBay

I'm thinking this used the same and it looks like they mention this in this picture "Condensor Pack"

Further, they then had the user connect a different condensor across block sections of track to carry the audio signal.

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Does anyone have a recording of a working Senco tender?

If you have, say, 12V AC (60 Hz) on the track, then if directly driving a 16 Ohms speaker that's a whopping 9 Watts of power flowing into the speaker.

Throw in a 248 Hz high-pass filter which attenuates the 60 Hz signal power by 12 dB which is better than nothing but I'm still thinking the low-frequency response of the speaker itself was a significant design parameter.  So while today everyone covets extended low-frequency (i.e., bass response) of 2" speakers in this application I'd think you'd be after more of a "mid-range" type speaker which then again might have been all that was available with the technology of the day.  Very interesting.

On the flip side, did the engine have any mechanism to block the audio signal from materially affecting engine speed?  I'm assuming the "mixer" box is cranking up the phonograph signal to many Volts.  So I wonder if this "system" had the same phenomenon as modern whistle/horn circuits where the engine speeds up when the phonograph is playing a relatively low-frequency whistle/horn sound?!

Anyone have a picture of the "TWO or more" (vacuum?) tubes that I suppose would be in the mixer box?!

Last edited by stan2004

Since posting this thread I've been able to get ahold of a mixer box - this is what it looks like inside:

I'd love to get my tender working if possible, but I wouldn't know where to even begin. The mixer box probably needs to be gone through, it's in rough shape, and I don't have anything capable of playing the 78 records.

@stan2004 posted:

On the flip side, did the engine have any mechanism to block the audio signal from materially affecting engine speed?

These didn't actually come with an engine - you were supposed to pair it with one you already owned, most likely an early postwar Lionel loco.

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The mixer box doesn’t take vacuum tubes, its much too small. It basically has connections for the transformer, track, and the turntable output. It likely relies on amplification from a stereo system to boost the power.

The mixer box contains 2-3 basic circuit components which includes at least one capacitor. I opened the case on mine but could not get at the components without unsoldering everything because they are wrapped up in paper to insulate them. Since my set is mint, I really don’t want to disect it.

The two-tube requirement seems to apply to the phonograph feeding the mixer box, and not the mixer box itself.

This seems to make sense because the output stage of the phonograph's amplifier has to be able to put out substantial power for this thing to work.  Stan suggested 9 watts.  Back in that era 9 was a lot.

A wimpy one-tube amplifier, which was something more appropriate for a headset than a speaker, just wouldn't do.

Mike

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The two-tube requirement seems to apply to the phonograph feeding the mixer box, and not the mixer box itself.



...

Right.  That's fascinating how the instructions suggest you need a minimum of 2 tubes!  I remember when transistor radios came out they were spec'd by how many transistors were in it.  You paid extra to get a 5-transistor radio vs. a 4-transistor radio.

OK. So presumably when going to buy a phonograph amplifier in 1950 you would tell the salesman that you needed at least a 2-tube phonograph system.  And if you had a good job maybe you could afford a 3-tube phonograph!

@Johnbeere posted:


...

I'd love to get my tender working if possible, but I wouldn't know where to even begin. The mixer box probably needs to be gone through, it's in rough shape, and I don't have anything capable of playing the 78 records.

These didn't actually come with an engine - you were supposed to pair it with one you already owned, most likely an early postwar Lionel loco.

It might not be that difficult.  My guess is the transformer might be functional but the condensors are shot.  But those can be replaced with modern condensors (i.e., capacitors).  Can you access and read any printed info on the condensors (it looks like 2 of them) like you can in the tender-side photo that has a condensor labeled "40mfd 150v.w. 225v.p."?

This may be getting into the technical nitty-gritty but I'm think the transformer is simply doing impedance conversion to couple the audio with the track voltage.  That is, since this system also supported DC track voltage it's unlikely the track voltage went thru the transformer since a transformer cannot pass DC power.

As for not having a record player I wouldn't worry about that for now.  There has been a nothing less than a renaissance in vinyl records so it will be simple to find someone to convert the records into some digital format like MP3 or whatever.  You need to get the system working using whatever audio source you have such as your phone, PC, CD player, whatever.  And then if you really want to go old-school with genuine spinning-phonograph and tube amplifiers there's the musician crowd that swears by tube amplifiers vs. the modern transistor/digital technology.

The actual nuts-and-bolts of how it works and then how faithful you want the restoration to be gets somewhat nerdy in terms of the technology but if you're truly determined to do so I think there's promise.  That and a nod to St. Jude, the patron saint of lost causes!

Last edited by stan2004

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