cd plays without preamp

Will this still occur with the preamp unplugged?

...Maybe something wrong with the power switch?

Are there tone controls on your preamp, or a method of selecting different sources? If there are and these work then I would agree that perhaps the unit is actually on. If not (and you could always just unplug to to eliminate that possibility) without looking at the schematic it would be impossible to say for sure - but - it is likely that your volume control is a potentiometer and you are feeding the signal through the rest of the passive components (resistors, coupling caps, feedback resistors). I would be curious to know if the volume is roughly what it was when the unit was obviously on, for the same position of the volume control.

There are tone controls on the preamp, more importantly the speakers get wired to the preamp, which I use for switching different sets of speakers in different rooms ( i.e. A speakers or B speakers along with A+B). This I coud understand the signals ran through the preamp, but how I could use the volume and tone controls at the same time with it turned off. I did not try unplugging the preamp because I now have my new preamp set up ( which does not have speakers wires to it as the Dynaco did ). I will have to go back and re- do everything to check if in fact the same thing will happen with the preamp unplugged. The volume control was definately in the same postion for the same volume as if it were turned on.

Rcme53 - from what you describe, it appears that the volume control is only acting as a rheostat to attenuate the incoming signal and that the preamp provides for only unity gain, if any active gain at all. I suppose that the tone control could also be passive. While completely passive preamps are not unheard of, generally if one goes to the trouble to include a power supply there are some active components that do more than provide for source selection.

Rcme53 - I was able to find that your Dynaco Pat5 has:

Magnetic Phono (LO) to Audio Out: 57 dB at 1 KHz.
Magnetic Phono (HI) to Audio Out: 63 dB at 1 KHz.
Magnetic Phono (LO) to Tape Out/E.P.L. Out: 37 dB at 1 KHz.
Magnetic Phono (HI) to Tape Out/E.P.L. Out: 43 dB at 1 KHz.
High Level to Audio Out: 20 dB.
High Level to Tape Out/E.P.L. Out: unity.

Is it possible that you used Tape-Out (gain=1) instead of Audio-Out (gain=20dB)?