  We report on our Chandra and RXTE observations of the bright old nova, V603
Aql, performed in 2001 April, supplemented by our analysis of archival X-ray
data on this object. We find that the RXTE data are contaminated by the
Galactic Ridge X-ray emission. After accounting for this effect, we find a high
level of aperiodic variability in the RXTE data, at a level consistent with the
uncontaminated Chandra data. The Chandra HETG spectrum clearly originates in a
multi-temperature plasma. We constrain the possible emission measure
distribution of the plasma through a combination of global and local fits. The
X-ray luminosity and the spectral shape of V603 Aql resemble those of SS Cyg in
transition between quiescence and outburst. The fact that the X-ray flux
variability is only weakly energy dependent can be interpreted by supposing
that the variability is due to changes in the maximum temperature of the
plasma. The plasma density is likely to be high, and the emission region is
likely to be compact. Finally, the apparent overabundance of Ne is consistent
with V603 Aql being a young system.
