Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fiftynine on December 30, 2016, 04:55:12 am

Title: Running a GZ34 Instead of a EZ81 from an AC15 Power Tranny in AC15 Style Build
Post by: fiftynine on December 30, 2016, 04:55:12 am

Can I somehow safely tap off 5v from the 6.3v heater supply to run a GZ34 instead of the EZ81 from a vintage style AC15 power tranny? It's a single channel build with 3 x 12AX7's, 2 x EL84's and hopefully the GZ34, by the way.


Cheers.

Title: Re: Running a GZ34 Instead of a EZ81 from an AC15 Power Tranny in AC15 Style Build
Post by: tubenit on December 30, 2016, 05:03:34 am

Why are you wanting to switch to a GZ34?  What are you hoping to accomplish?

I don't know if you can lower 6.3v to 5v effectively?   Doug Hoffman sells 5v trannies for about $20.  You could use one of those.

With respect, Tubenit

Title: Re: Running a GZ34 Instead of a EZ81 from an AC15 Power Tranny in AC15 Style Build
Post by: fiftynine on December 30, 2016, 05:38:30 am

I want to match up a GZ34 into a vintage style AC15 tranny mainly for the safety of the rectifier having it's own heater. I reckon the draw from the 12AX7's that are missing in a single channel version will cover the demands of the 5v to the GZ34. Just finding a safe way to do it, I guess.

Title: Re: Running a GZ34 Instead of a EZ81 from an AC15 Power Tranny in AC15 Style Build
Post by: sluckey on December 30, 2016, 05:54:36 am

Quote

Can I somehow safely tap off 5v from the 6.3v heater supply to run a GZ34 instead of the EZ81 from a vintage style AC15 power tranny?

No. The GZ34 has the cathode internally connected to the filaments. This means that B+ will also be on the entire filament string!

You can certainly run a GZ34 from a 6.3V source by including a series dropping resistor. BUT THE FILAMENT WINDING CANNOT BE SHARED WITH OTHER TUBES.

Quote

I want to match up a GZ34 into a vintage style AC15 tranny mainly for the safety of the rectifier having it's own heater.

What safety??? EZ81 also has "it's own heater". And even better, it ain't connected to the cathode. The EZ81 is a perfect match for any 2xEL84 amp.

If you still want to run a GZ34, get a proper PT or get a separate 5VAC filament transformer.

Title: Re: Running a GZ34 Instead of a EZ81 from an AC15 Power Tranny in AC15 Style Build
Post by: fiftynine on December 30, 2016, 02:35:15 pm

Quote from: sluckey on December 30, 2016, 05:54:36 am

This means that B+ will also be on the entire filament string!

Ouch. Thanks, man.