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lowering B+,with a voltage divider?

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2/10/2000 9:37 PM
Max	lowering B+,with a voltage divider? Hi everybody! Would it be possible to lower B+ with a voltage divider? Thanks for anny help. Best regards. Max.

2/10/2000 10:36 PM
Don Symes	Possible? yes. Practical? NONONONONONOnononono! The divider will dissipate tremendous heat and will cause horrendous sag - bad enough to have the sound cutting out. The zener diode trick is the simplest way to go, and www.aikenamps.com has a circuit that allows you to use a 1W zener for this application.

2/11/2000 2:42 AM
Max	Hi Don! Thanks for your reply. But do you think that the zener trick would work for lowering B+ from 425V to 270V? That is for a class A/AB switch. Thanks again,and best regards. Max.

2/11/2000 4:29 AM
Don Symes	What kind of current are we talking about here? 155V * current = a big heatsink on you rpass element.

2/11/2000 7:44 PM

Hi everybody!

Don,i'm working on a bassman(BF)then we're talking of the curent for the 6L6,class A,aproximately 170mA for 270V B+.
I have checked the Actual B+ It's 406V,because i'm runing it with 106VAC on the primary.
I have exagerated the voltage drop,i need~ -70V on B+.
The rest of it will be taken away by the valve rectifier.

Do you think i can lower B+ with the zener trick?

Thanks to all for the help.
Max. =

2/11/2000 10:54 PM
Don Symes	Dropping 70V at 170mA is going to be about 12W that your zener or pass element will need to dissipate. That's a pretty big heatsink to find room for. At that wattage, I'd also recommend some kind of thermal grease. Read up on the topic and double-check your math. That said, while I like Corwin's suggestion, the zener should do it.

2/11/2000 5:11 AM
Corwin	a choke input filter would be better for this application. or using a 180-0-180 PT and bridge recto with a switch from grounding the PT CT(Class A voltages) or the negative terminal of the bridge recto(Class AB voltages). Both options would require rebiasing for Class A and AB of course.

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