I picked up a box of miscellaneous Lionel train and parts. I've been able to identify everything in the box but this one small part. Any idea what it is or what it might be from?? And yes, I do know the round shaped object is a dime!! 
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It's a crystal used for oscillator circuits, this one at 27.255 MHz.
Used for TMCC CAB-1 to Base/Powermaster radio circuits. (also used on very old CB radios 
Channel 23 in this case...I'll admit I looked that up, I don't have them memorized...)
-Dave
I think it is a crystal for an early Citizen's band or ham radio transmitter. The 27,255MHz is the frequency the crystal resonates at and hence the frequency the transmitter would transmit at if the crystal were inserted. One would have a bunch of the crystals and change them to change frequency.
Unrelated to toy trains.
@Dave45681 posted:It's a crystal used for oscillator circuits, this one at 27.255 MHz.
Used for TMCC CAB-1 to Base/Powermaster radio circuits. (also used on very old CB radios
-Dave
Interesting as there was a PowerMaster #71-2867-250 in the box! I just pulled the plug out of the side and there it was. I found 2 manuals in the box and only 1 PowerMaster. Maybe one of them met its demise and this was the only part left.
Thanks!!
I'm with Dave. On the old TMCC units the way to change the channel was by changing the crystals.
That way in a "trainshow" type setting where there were multiple TMCC layouts you could avoid intereference.
Lionel overcame this hiccup with Legacy providing 9 different channels, already preprogrammed into the system.
Dave is 100% correct. It is a crystal for TMCC operations at least in this case.
I defer to the other experts. I was unaware of the early TMCC use of crystals.
Bill
Looks like the crystal from the TMCC CAB1. It's actually in a socket in case you want to change frequencies, there was at least one alternate frequency crystal available. It's under the battery cover.
The base also had a crystal, but a fun fact is that it's frequency was 455khz lower than the actual operating frequency. There is a demodulator that decoded the 455khz FSK signal. The little "bump" on the side of the base is the little pull-out drawer for the base crystal.
Dale Manquen had conveniently taken pictures of the boards so I didn't have to take one apart. 
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@gunrunnerjohn posted:Looks like the crystal from the TMCC CAB1. It's actually in a socket in case you want to change frequencies, there was at least one alternate frequency crystal available. It's under the battery cover.
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The base also had a crystal, but a fun fact is that it's frequency was 455khz lower than the actual operating frequency. There is a demodulator that decoded the 455khz FSK signal. The little "bump" on the side of the base is the little pull-out drawer for the base crystal.
Dale Manquen had conveniently taken pictures of the boards so I didn't have to take one apart.
Good reminder. Also not a coincidence that CB radio crystals came in transmit/receive pairs separated by that same 455 kHz. Not that CB was FSK, of course, but still used the popular 455 kHz.
-Dave
In CB radios, the 455khz is the IF frequency.
Early VHF (pre-synthesizer) radio scanners also employed similar individual plug-in crystals for the different public service and railroad frequencies. The advent of digital scanners and 800 MZ trunked radio systems rendered such crystals virtually obsolete.
I'll say Art, I remember radio scanners with a whole row of crystals.
@Tinplate Art posted:Early VHF (pre-synthesizer) radio scanners also employed similar individual plug-in crystals for the different public service and railroad frequencies. The advent of digital scanners and 800 MZ trunked radio systems rendered such crystals virtually obsolete.
Crystals were pretty much obsolete long before trunking and digital modes became common, I'm pretty sure. I'm certain you are correct on the synthesizer aspect being what killed them.
I recall many of the scanners my father had in the mid to late 80's onward (Pro-30 being one of the earlier hand held units he had - 16 channels - woo hoo! followed by the pro-32, 34, 43, etc....) and they were all programmable via keypads, no crystals. Those scanners were many years earlier than the mass implementation of trunking and the digital formats that are in most scanners today.
(Though I do recall a few straggler hand held CB units Radio Shack used to sell in that era that still used crystals. One was a whole three channels of the 40 with an A/B/C switch on the front! High tech! Some of the pairs you could walk into RS and buy off the shelf probably into the early 90's, others you had to order special)
-Dave
At one time Lionel had 4 sets of different send/receive sets of crystals.
I only ever saw one alternate set, but I figured there must be others. There weren't any "channels" you could select, so you had to change the crystal if you had two layouts in close proximity.
When my wife and I took an extended Amtrak trip across the US in 1981 from Chicago to San Francisco and from there to Seattle and then back East to Milwaukee and Chicago, I had a four-channel crystal controlled Bearcat scanner. I had road frequency crystals for each railroad we travelled over. On one train, a conductor actually asked me if my unit could transmit and I assured him it could not. He later rewarded me with a set of train orders and an official timetable.
Wow...a blast from the past.
That is a crystal for channel 23 in the Citizens Band...the CB Band for short. 27.255 MHz is channel 23. Early CB radios used these crystals the set the transmit and receive frequency. TMCC also uses this frequency.
I say a “blast from the past” because in the heyday of CB radio (the 1970s) I owned a very busy CB shop. It was called “Boss Radio” and I handled the service side of the business. During that decade, I repaired over 5,000 CB radios.
Perhaps interestingly .. these 27mHz Crystals were used here in Australia for early AM Radio Control units for aircraft cars and boats
In the 70's and 80's pretty much any cheapo Japanese RC toy was on the 27 band
There was also a crystal in the early power master as the cab-1 talked directly to the power master. This was before the TMCC base was released and allowed the cab-1 to run trains in the conventional mode.
It was one of the ground crystals for RC stuff. Aircraft used another for separation. Back in the day you had to get together to make sure nobody was using the same frequency at the same time. Now they all talk to each other and this system is pretty much extinct.
