Can you guess what this is for vintage audio gear?

[Michaels HiFi]

My guess is most people won't know what it is or what it does and WHY it's so important to use on new vintage or newly repaired gear.

I bet Ralph will know what it is...

 

[MikeCh]

I know what this is. DBT/crude ICL.

 

[Speedskater]

It's a dim bulb starter. It limits turn-on AC current. It allows old power supply capacitors to re-form slowly.
Also in components that have a serious problem, it prevents blowing the power supply fuses.

 

[Michaels HiFi]

It's a dim bulb starter. It limits turn-on AC current. It allows old power supply capacitors to re-form slowly.
Also in components that have a serious problem, it prevents blowing the power supply fuses.

Exactly!

It's something I use when I receive new vintage tube testers / complete internal restoration when turning them on.

Rather than spending the money on a Variac, an EE friend made this for me.

 

[Bones13]

Used one of those whilst I was DIYing Nelson Pass amps. (With a Variac)

 

[Barry]

I used something like this when I had a Phase Linear 400 with a 200,000 uF power supply. That bulb was blindingly bright when I turned the amp on