[sdiy] converting output from a RAM to CMOS

[mark verbos]

I'm doing a module where all the logic is CMOS at 15 volts, but there  
are some 4164 RAM chips running at 5 volts. Getting control signals  
and data into the RAM is easy enough, using a 4049 powered from +5,  
but I'm having a little trouble getting back to 15 volts. I used a  
2N3904 with a 4.7k resistor to the base and a 10k from the emitter to  
ground, power to collector and took the output from the emitter. The  
data at the RAM seems to be drained, as it slews back to ground at  
each step. What gives? Does it need a pull up resistor? Am I loading  
the output?

I realize that perhaps a better option would be to use a TTL buffer  
with a pull-up to 15 volts, but I'd like to not make a new PCB. I  
looked at a Deltalab delay schematic, which uses the same RAM and they  
did an interesting thing for this. The data from the 4164 goes through  
a 9.53k resistor with a .01 cap in parallel then there's a 16.2k pull  
up resistor  then to the CMOS. There's a diode from the RAM output to  
+5 to protect the RAM from overvoltage going backwards. They are only  
using +12 volts, but is something like this a better option for me  
than the transistor? I could kludge this into my PCB layout if need be.

Any incite appreciated,

Mark