Changing frequency of a receiver

Is changing the reception frequency in a receiver as simple as changing the crystal?
My wife is expecting very soon and we have those baby monitor thingies, a transmitter and athe corresponding receiver. We want another receiver unit and i happen to have an old(ish) speaker from a cordless speaker system. Upon opening these units i have found the baby units to be switchable between a 16.64 MHz xtal and a 16.65 MHx xtal but the cordless speaker has a different xtal.
Would i just be able to change the crystal in the cordless speaker to a 16.64 or 16.65 xtal (or change the xtals in the baby rtransmitter, receiver and cordless speaker to the same frequency xtal?)
Ant help would be fantastic, cheers!

Tell us what the original frequency of the crystal in the "cordless speaker" is. I ask this because the frequency of the xtal is typically multiplied. Also in a reciever, the multiplied xtal frequency is usually added to or subtracted from the IF frequency which is typically 10.7Mhz in cheap FM recievers. So it would help to confirm the IF frequency also.
Sometimes the actual Tx frequency is printed on the case of the device also.

I have just found the transmitter to the "cordless speaker system" in a lengthy rummage and it has printed on its case, `49.83 to 49.98 MHz`. Inside the transmitter however is a 16.62 MHz xtal and inside the receiver is a 49.8 MHz xtal.
Inside the baby whatsit transmitter are a 16.64 and 16.65 MHz xtals (channel 1/2) and in side the receiver are a 49.465 and 49.495 MHz xtals.
So could i actually just leave the xtal as is and just adjust the variable inductors to `tune` to the correct receiving frequency.
I cant believe i havent just plugged in and tried it! Looking at this and from that little bit of info you gave me all the info i needed to know wether this would work or not was staring me in the face!
Yep, i just plugged and tried just now and they work together no probs! Cheers anyway (boy do i feel stupid!)

The "baby monitors" transmit on frequencies around 49.95Mhz, ie three times the crystal frequencies found in the transmitter. What the crystal frequency would be in the reciever would depend on the IF frequency.

The frequency on which your "cordless speaker" operates, I have no idea, I have never heard of such a thing before. If you can tell the crystal frequency in the speaker, it may be possible to tell if it could be moved onto the baby monitor frequency, but I dont hold much hope.


Edit:

I have just read your second message, posted as I was typing.

The baby monitor recievers hav a 455 khz IF going by the recieve crystal frequencies.
The remote speaker transmits on 49.86 Mhz, but the reciever with the 49.8Mhz crystal does not make a lot of sense.

However, if they work together, good luck.
Also, be aware that these things can be heared over quite a wide area, be carefull what you say or do when they are switched on!

JimB

Cheers for the extra info.

Incase you`re interested (probably not!) the cordless speaker system was something i found at my grandma`s house after my grandad died! Its a "Magma sound 3000" !?!? The base unit consists of an on/off sw, mic/audio sw and a single 1/4" stereo jack. The speaker unit (i could only find one!) is only a few inches high and rated at 3W at 4ohms and contains vol and bass boost!