I don't know what you mean by "small resistor" in series with the V+ line.
Each amplifier stage should have a series resistor of 100 ohms and a bypass
capacitor of .01uF. Actually, you can bypass every other stage if you are
using common emitter or common source stages, but I would do it with every
amplifier stage.
As far as physical distance for each stage, you should allow 1/2 inch for
every 40dB of gain. You shouldn't have this type of problem. A ground plane
is always a good idea, but at the very least you should have quite a bit of
ground flood on the circuit board. Although it is possible if you have quite
a bit of copper foil tape around the board, you can build this circuit on
perfboard but you have to be very careful, as you have already discovered. I
don't know if they have perfboard that has copper on only one side, but this
is one solution.
You had a question about the old hand-wired tubed equipment. With a metal
chassis, you would keep the wiring down close to the chassis itself, which
would in effect provide that ground plane. A ground is very important to
provide a place for the return currents for all of the signals, whether
physical wires or copper traces are used.

Pete

wrote in message
ups.com...
I'm attempting to build a small AM broadcast superhet transistor radio
from scratch and having a problem with the three IF stages oscillating
at the IF frequency (455KHz). The IF coils are salvaged from other
radios and the ground connections are to a common bus wire that
connects all the IF coil shields. It works reasonably well around 5
volts, but breaks into oscillation (at the IF frequency) if the supply
voltage is increased 1/2 volt and the signal drops off significantly if
the supply voltage is reduced 1/2 volt. So, it only works within a very
small supply voltage range of around 5 to 5.5 volts. The IF stages are
decoupled from the supply with a small resistor in series and bypass
cap to ground which helps, but doesn't solve the problem. I'm wondering
what can be done to stop oscillations and increase gain?

How did they manage to avoid the oscillation problems in the old tube
radios that were hand wired without any PC board?

-Bill