Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Diverted on November 14, 2018, 09:54:50 am

Title: Zener diode placement
Post by: Diverted on November 14, 2018, 09:54:50 am

Hi all,

I'm building a Fender standalone reverb clone, with a power transformer that puts out about 310v with no load. I'm expecting it'll still be a little high once I get it all wired up. The HV secondary does not have a center tap. I've used Zeners before to reduce voltage, putting them in the center tap leg. Without that center tap, I'm wondering about placement. Assuming I just run them on one of the two HV taps?

Thanks!

Ted

Title: Re: Zener diode placement
Post by: sluckey on November 14, 2018, 10:03:00 am

Put the Zener between the bridge positive terminal and the filters. Or put it between the bridge negative terminal and ground.

Title: Re: Zener diode placement
Post by: d95err on November 14, 2018, 10:07:54 am

You could simply use a resistor between the rectifier and first filter cap to bring the voltage down. As it’s all class A, it will not introduce any sag. You will also get better filtering (less hum/buzz).

Title: Re: Zener diode placement
Post by: Diverted on November 14, 2018, 03:11:15 pm

Thanks for the tips! I'll try various resistance until I find something in the ballpark. Much obliged,

Ted

PS: Using 10-25W resistors dependign on value.

Title: Re: Zener diode placement
Post by: shooter on November 14, 2018, 08:46:54 pm

If it's anything close to this one;
http://el34world.com/Hoffman/files/Hoffman_6G15.pdf

I think

Quote

310v with no load

will fall really close to a good spot loaded