Modern capacitor replacement for tube audio

Question

I have a Dynaco PAS 3 pre amplifier from the early 1960s that has been in storage for years.

I have been led to believe I should replace the capacitors in a couple of the boards. I have read your information on hype vs performance.

I have a list of what I need. They tend to be 400 V 0.002 to 1.0 mF capacitors but there are others too.

What type of modern capacitor would I use if I wanted the correct capacitance in the circuits?

My major concern is with value and durability. I have very little interest in esoterics, I just want the thing to work.

Answer 1

Shotgun replacement of capacitors is an unwarranted fetish. To be sure SOME capacitors degrade with age. But others are as good or even better than modern replacements. Wet electrolytic capacitors are subject to drying out and/or leaking over time. They loose their capacitance and cause audible symptoms.

Capacitors used for power filtering will allow mains-frequency ripple to enter the circuit which will be heard as hum. This is a prime symptom that filter or bypass capacitors need to be replaced.

The smaller value (0.002 to 1.0 uF) capacitors will be found in DC-blocking, AC-coupling capacitors in-line with the audio signal. If they lose value, it will be audibly apparent as loss of low-frequency response.

Other uses for smaller value capacitors will be in places like tone controls. And a change in value will result in the tone controls acting differently or even failing completely.

Note that those old fire-bottle circuits need high voltage capacitors which are rather uncommon in modern times of solid-state circuits. There are vendors online who specialize in components used in repair and construction of tube circuits.

Suggest actually evaluating the gadget before making any component replacement decisions. As the old saying goes: Don't try to "fix" something that ain't broke.