Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: goldstache on December 21, 2016, 03:46:18 pm

Title: DC elevated heaters and Fender 6.3 Jewel bulb
Post by: goldstache on December 21, 2016, 03:46:18 pm

I have a CF stage in a new build and I think the elevated heater supply is frying the Fender style 6.3v bulb. 

I have about 90VDC on the filaments and my CF stage cathode is at about 154VDC.  Seems legit.

Does anyone have any experience with bulbs frying from high float voltages?

Does anyone know the max DC these 6.3 bulbs can handle?

Thanks

Title: Re: DC elevated heaters and Fender 6.3 Jewel bulb
Post by: sluckey on December 21, 2016, 04:30:26 pm

Elevated heater is not an issue with the indicator lamp if the lamp is wired correctly. Show us your schematic.

Title: Re: DC elevated heaters and Fender 6.3 Jewel bulb
Post by: goldstache on December 21, 2016, 05:04:54 pm

Don't have it handy but it's the first in the string and the elevation point enters there at the jewel.

Elevation:
B+ > 180K > 47K (cap here to ground) >ground

second bulb is in and going strong after 30 minutes. 

Title: Re: DC elevated heaters and Fender 6.3 Jewel bulb
Post by: sluckey on December 21, 2016, 05:31:49 pm

Quote

the elevation point enters there at the jewel.

If I understand this correctly, your lamp and all your tube filaments are at risk.

The elevation point should be the filament winding centertap. If there is no real centertap wire on PT filament winding, you should create an artificial centertap using two 100Ω resistors. The elevated voltage would connect to the junction of the two resistors.

Title: Re: DC elevated heaters and Fender 6.3 Jewel bulb
Post by: goldstache on December 21, 2016, 05:37:46 pm

I'm sorry.  My filament CT is where the float is.  Then filament runs to the jewel on down the line. 

Title: Re: DC elevated heaters and Fender 6.3 Jewel bulb
Post by: PRR on December 21, 2016, 11:29:45 pm

Bird on a wire. Neither leg of the jewel knows it is 150V up so it is fine.

Title: Re: DC elevated heaters and Fender 6.3 Jewel bulb
Post by: goldstache on December 22, 2016, 07:55:42 am

Thanks, second bulb is still glowing after many hours so me thinks it's fine.  False alarm.