Does anyone out there have any idea why me 1948 RCA Victor radio has plenty of volume but when I switch over to the phonograph, the volume is extremely low. I can turn the volume all the way up and can barely hear anything coming out of the speaker. The radio works great. Tried cleaning the needle with some alcohol, did not help. I took the chassis out and cleaned all contacts on the rotary switch, did not help. The radio has not been recapped. Could I possibly have a weak pickup cartridge?

I restore the RCA record players and 99.9% of the time the crystal cartridge is bad, which is probably your case. Ceramic element cartridges took over on the '50's, which last quite a while and are more durable.

If you touch the wires from the cartridge you should get a loud buzz. If so your cartridge needs to be rebuilt or replaced.

:If you touch the wires from the cartridge you should get a loud buzz. If so your cartridge needs to be rebuilt or replaced.
:
:
If the cartridge is bad is there a suitable substitute?

Bad cartridge. These older cartridges used piezo transducers made from Rochelle salt crystals, which are sensitive to humidity and will eventually "go bad" just sitting around.

DEAD . . . . (R.I.P) . . . . Crystal cartridge. . .

Being circa 47-48 and if its "crystal" cartridge is using this large pot metal kluge shown . . . . . .

and you additionally tried the aforementioned "buzz" test while being in the phono position,

with its volume to the max and then "stroked" its needle top , OR, the yoke that it clamps

into ( in case its needle is completely missing) and you then didn't hear that stroke being loudly

reproduced. . . . . . .

Then check out:

http://www.youtube.com/watch?v=3ZJ9zyWixWM>

for its info.