Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: clyde on March 18, 2015, 08:54:12 pm

Title: Filament Overvoltage
Post by: clyde on March 18, 2015, 08:54:12 pm

I'm planning on using the 115v tap on a Hammond PT, needing the boost in voltage but am concerned about filament voltage being too high.  Lowering the 6.3v tap can be done with either diodes or resistors as I understand.  Any preferences and why?  However, how do I handle the 5v rectifier tap? 

Title: Re: Filament Overvoltage
Post by: lkrasner on March 18, 2015, 09:35:08 pm

I would be very surprised if the higher voltage caused any issue. Maybe tube life will be decreased a bit. If you want to be safe, just put a resistor in. It's simple and reliable.

Calculate your total filament current, then use ohms law to figure out what resistor you should use to drop it down to 6.3.

Title: Re: Filament Overvoltage
Post by: kagliostro on March 19, 2015, 02:11:23 am

Ditto for the 5v winding


K

Title: Re: Filament Overvoltage
Post by: clyde on March 19, 2015, 09:06:03 pm

And the B+ on the 5v winding?

Title: Re: Filament Overvoltage
Post by: sluckey on March 19, 2015, 09:49:18 pm

Quote from: clyde on March 19, 2015, 09:06:03 pm

And the B+ on the 5v winding?

Should not be affected.

Title: Re: Filament Overvoltage
Post by: clyde on March 19, 2015, 11:06:12 pm

Cool, thanks.

Title: Re: Filament Overvoltage
Post by: clyde on March 23, 2015, 05:31:13 pm

Good old RG, always on top of things.  It isn't exactly what I'm needing as I want the higher B+ running the PT on the 115v tap, just worried about the filaments running at 7.1v. 

Title: Re: Filament Overvoltage
Post by: Willabe on March 23, 2015, 07:40:53 pm

Quote from: clyde on March 18, 2015, 08:54:12 pm

I'm planning on using the 115v tap on a Hammond PT, needing the boost in voltage but am concerned about filament voltage being too high.  Lowering the 6.3v tap can be done with either diodes or resistors as I understand.  Any preferences and why?

Here's the 1st post guys. ^

He needs the extra B+dcv. So a bucking transformer is out.


                 
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