Dim Bulb Tester gets brighter as volume is increased.

[czgeddes]

I’ve just begun a restoration of a HK 730 Twin and have enjoyed listening to the radio with it for the last few months. I put it on the DBT and as I turned up the volume the light got brighter! Is this normal?

 

[llwhtt]

Yes, the louder the more current the brighter the bulb.

Craig

 

[avionic]

I put it on the DBT and as I turned up the volume the light got brighter! Is this normal?

Yes.

 

[czgeddes]

Yes, the louder the more current the brighter the bulb.

Craig

Many thanks!

 

[czgeddes]

Yes.

Thanks.

 

[Skywatcher]

I’ve just begun a restoration of a HK 730 Twin and have enjoyed listening to the radio with it for the last few months. I put it on the DBT and as I turned up the volume the light got brighter! Is this normal?

Yes because the unit is drawing more current, and the filament is limiting the current. However it is not "normal" to run a unit on the DBT for any more than just testing. Turn the BIAS current down, disconnect it from the DBT, plug it into the wall directly, and adjust the BIAS current to spec. Then you can crank it all you want.

Starving any unit of current while on a DBT can be destructive. At idle, or very low volume is fine though.

 

[Warren-Oates]

also depends on the wattage of the bulb, a 40w would start glowing pretty quick with some volume on the 730. a 100w bulb might not glow at all with the same volume.

 

[czgeddes]

Yes because the unit is drawing more current, and the filament is limiting the current. However it is not "normal" to run a unit on the DBT for any more than just testing. Turn the BIAS current down, disconnect it from the DBT, plug it into the wall directly, and adjust the BIAS current to spec. Then you can crank it all you want.

Starving any unit of current while on a DBT can be destructive. At idle, or very low volume is fine though.

Thanks skywatcher. It is what I intended and plugged it into the wall. When the lightbulb got brighter (120W bulb) I thought it had a short at higher volumes. I’m a newbie and thanks for the reply