Electrical properties of cleared resin?

Hello. I may have an opportunity to produce some replacement parts for vintage (and diy) tube microphones.

The tubes can run in excess of 700 volts and the circuitry is very sensitive to interference.

The originals were either acrylic or injected plastics. There is some thought that the type of plastic may have some interplay with the final sound of the microphone.

Any thoughts or experiences?

Thanks
Mac

The plastic probably has an effect on the sound in much the same way that the construction and materials used for a Violin affect the sound.

Cured resin softens up quite a bit when it gets warm. Vacuum tubes tend to dissipate a fair amount of heat. This may be a problem depending on what you’ll use the printed parts for. I just put an Ohmmeter on a piece of Tough V4 print and it reads open circuit. I have an insulation breakdown tester somewhere that’d tell us the dielectric constant of the cured resin. But I expect it’s at least as high as air and probably higher… electrically it’s unlikely to be a problem.

This is a very important point as the change in the mechanical properties will probably affect how the microphone records the sound.

@maq3396 once you have some of the electrical properties of the resin, this would probably be a good question for a place like www.reddit.com/r/askengineers/ or www.reddit.com/r/audioengineering/ . There’s loads of good willing & knowledgeable people there.

It doesn’t look like this is listed on the datasheets, but I have a few numbers that might help out.

Using the ASTM D150-11 Dielectric Constant & Dissipation Factor

Tested Frequency: 60Hz
Dielectric Constant ‘k’: 3.72

Tested Frequency: 1kHz
Dielectric Constant ‘k’: 3.33

Tested Frequency: 1MHz
Dielectric Constant ‘k’: 3.16

Using the ASTM D149 Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies

The breakdown voltage can be approximated at 100kV/mm

Let me know if these are helpful and what sorts of values you’d be looking for.

2 Likes

Thanks everyone.

It seems that the community would rather have a vacuum formed part so this will go into the archives for now.

The issue of heat is salient…The tubes for recording microphones are very underdriven and the chasis of the microphone never passes “mildly warm”.

In terms of the electrical properties I will check out the other forum as well.

Have a great day all!

Cheers
Mac