Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mresistor on April 13, 2023, 02:30:01 pm

Title: LBL on Variac ?
Post by: mresistor on April 13, 2023, 02:30:01 pm

Can variac be run safely on a light bulb limiter?

Title: Re: LBL on Variac ?
Post by: sluckey on April 13, 2023, 04:37:06 pm

Quote from: mresistor on April 13, 2023, 02:30:01 pm

Can variac be run safely on a light bulb limiter?

Sure. But I can't think of a single good reason to do so. What's your objective?

Title: Re: LBL on Variac ?
Post by: mresistor on April 14, 2023, 08:22:39 am

I should have been more specific.  I was wanting to use it at the input to the variac. Guess it would work there too.   Thanks.

Title: Re: LBL on Variac ?
Post by: pdf64 on April 14, 2023, 09:19:43 am

I suggest
Mains -> variac -> LBL -> load

Title: Re: LBL on Variac ?
Post by: kagliostro on April 14, 2023, 09:33:34 am

I think he was planning to use the LBL before the Variac because the lamp is chosen in reference to a specific voltage and wattage and resistance is strictly joined to it in a lamp

But May be it will act correctly also if connected after the Variac

Franco

Title: Re: LBL on Variac ?
Post by: acheld on April 14, 2023, 10:56:34 am

Or, maybe he is worried about his Variac!

Title: Re: LBL on Variac ?
Post by: pdf64 on April 14, 2023, 11:11:29 am

Ok, I was under the impression that a variac would draw a high initial current surge, then a fair bit of magnetising current.
I thought that might keep a lower wattage bulb bright.
On checking mine, the initial surge current is high, but the magnetising current seems to be negligible.

I think either way around would be ok.
 

Title: Re: LBL on Variac ?
Post by: mresistor on April 14, 2023, 11:21:17 am

Well I actuall tried it and it wasn't creating any harm.  But as pdf64 stated using the LBL between the load and the variac is a better method.