royce 640

[chugers]

Another ebay special Royce 1-640 paid $15 for radio.
I would like to change out the 1-4 channel crystal to be able to receive 27.385
from what info I can find this should be a 23,730.
Does anyone know if this is correct and where I might find one.
Thanks Chugers

[Tombstone (R.I.P.)]

Ok, seems they had two systems of mixer crystals in that radio, early/ late if you desire. The early model had 7 MHZ crystals for mixers, sounds like you have the version with the 23 MHZ Mixers. I did the math as best I could and came up with 23.740 for the mixer you want to go to to get up to channel 40 and it would include channel 38. I might be off on my calculation and yours might be the right frequeny crystal. Someone on this board can probably jump in here and tell you the exact crystal frequency that you need. When you add these higher channels you'll probably have to retune the transmitter for an even spread of power if you plan to transmit on them. Best I can do, good luck!

Tombstone

[Sandbagger]

Aug 25, 2008 17:19:57 GMT -5 Tombstone (R.I.P.) said:

Ok, seems they had two systems of mixer crystals in that radio, early/ late if you desire. The early model had 7 MHZ crystals for mixers, sounds like you have the version with the 23 MHZ Mixers. I did the math as best I could and came up with 23.740 for the mixer you want to go to to get up to channel 40 and it would include channel 38. I might be off on my calculation and yours might be the right frequeny crystal. Someone on this board can probably jump in here and tell you the exact crystal frequency that you need. When you add these higher channels you'll probably have to retune the transmitter for an even spread of power if you plan to transmit on them. Best I can do, good luck!

Tombstone

The Royce has a somewhat confusing synthesizer. Or more accurately, the way it's been presented is a bit confusing. Some see 7 Mhz main oscillator crystals, others see 23 Mhz. Actually they're pretty much the same. 7 Mhz is the crystal fundamental frequency, while 23 Mhz is the 3rd overtone, and is the actual frequency that gets mixed with the 14 Mhz mixer oscillator and the 11.2 Mhz carrier oscillator.

Interestingly, for channel's 36 - 40 (skipping 39), I come up with a split between what you guys found. I come up with 23.735. I'm pretty sure the reason for that is due to the "rounding" of the crystal frequency and the fact that the crystals are cut "high" and trimmed down a couple of Khz for the actual frequency.

Look at what is stamped on the crystals in the radio. If they're marked 23 Mhz and they end in a "0", then go with .740. If they end in a "5" then go with .735.

[Tombstone (R.I.P.)]

Thanks for jumping on here, Sandbagger. That is a bit confusing trying to calculate the proper crystal frequency that he needs and I saw the notation about the "high" cut crystals.

Tombstone

[dgtr43]

Ok, since you purchased the Royce 640. Can you tell me where I can purchased output finals for a Royce 621, might have the model # wrong. The schematic says they are 2SC756A.

[Sandbagger]

Sept 8, 2008 15:56:06 GMT -5 dgtr43 said:

Ok, since you purchased the Royce 640. Can you tell me where I can purchased output finals for a Royce 621, might have the model # wrong. The schematic says they are 2SC756A.

Those are TO-5 case style transistors which are probably discontinued along with a ton of other similar parts. Most modern CB radios use the more common TO-220 case power tab style.

But all is not lost. It's not necessary that you use the EXACT same part for it to work. The circuit is not that critical. You may be able to find substitute parts from places like RF Parts. You could also retrofit a TO-220 case part to work. It won't be a drop in replacement, but if you bend the leads properly and fashion a sufficient heatsink or find a way to attach to the existing mount, it should work ok. I have done this in the past.