Zenner trick??? Where's the schemo?

[Satamax]

Hi everybody!

I have made several years ago, that Transistor/Zener thing to reduce the voltage. I found the explanation in Aiken's site, but can't find the schemo or anything else anymore on the web! Searched old ampage, Mark Huss states it, but tells the same, can't find anything on it! I thought it was still on Steve's A site, no luck either! I basicaly have 3 wires out of it, and can't make sense of it anymore

Anyone's got A link???

Thanks.

Max.

[Mark Black]

Wasn't that R.G.'s doing?

If so it's at the bottom of this page:
http://www.geofex.com/Article_Folder...osfetfolly.htm

[Satamax]

Thanks a lot Mark!

Well, IIRC that's the same. But i made it with a BU806, and i think it's Enzo who walked me through, as i was even more of a beginer in electronics than now.

[Satamax]

Can't for the sake of me remember if i need to ground the casing and the clear blue wire!

[Satamax]

Grounded it doesn't work! I'm pretty stumped!

[Satamax]

Can't remember where the colector, emiter and base should go!

[R.G.]

It was an old trick before Randall or I adapted it. We each did it slightly differently. I prefer the toughness of power MOSFETs, Randall did it with bipolars if I remember right.

In the one at GEO, you MUST add a 12V zener, cathode to gate, anode to source on the MOSFET to protect the gate against transients. The schemo at GEO is my first hand-scribbled sketch, not a fully developed result.

Yes, you ground the drain of the n-channel MOSFET when you use it in the ground side.

You can use it in the high side with no grounding, but then it's dangerous as it floats up at B+. Using the ground-side version, the drain needs to be grounded and this makes a safe and convenient way to heat sink it by bolting it to the chassis. Use heat sink grease.

[Satamax]

Hi RG!

Thanks a lot for your reply! I tried it isolated from the chassis with a heatsink and all, doesn't work either. I hope i haven't blown the darlington, that was the last in my stash! Well, drawn a litle schemo, but this seems weird!

Basicaly the NPN darlington has emiter to ground, colector to centertap, and the zener is betwen colector and base. I can't remember where this thingy was going when i tried to lower the bassman voltage. I was persuaded that it was on teh centertap, but i have no brain! Basicaly, it's similar to the circuit at the botom of this page? http://www.bcae1.com/diodes.htm

I should admit that i understant fcuk all NPN would mean that colector and zener on the colector side should be grounded, and i should use use the centertap on wht is the ground on my schemo???

Thanks a lot for your help.

Bye.

Max.

[R.G.]

Hi RG!

Thanks a lot for your reply! I tried it isolated from the chassis with a heatsink and all, doesn't work either. I hope i haven't blown the darlington, that was the last in my stash! Well, drawn a litle schemo, but this seems weird!

Basicaly the NPN darlington has emiter to ground, colector to centertap, and the zener is betwen colector and base. I can't remember where this thingy was going when i tried to lower the bassman voltage. I was persuaded that it was on teh centertap, but i have no brain! Basicaly, it's similar to the circuit at the botom of this page? http://www.bcae1.com/diodes.htm

I should admit that i understant fcuk all NPN would mean that colector and zener on the colector side should be grounded, and i should use use the centertap on wht is the ground on my schemo???

Thanks a lot for your help.

Bye.

Max.

Your schemo is incorrect. Exchange the ground and centertap connections. The centertap is more negative than the ground.

NPN means that the collector needs to be the most positive point, the emitter the least positive/most-negative point. From the transformer/rectifier side, the + rectified side is the most positive, goes through the circuit to ground, and then out to the centertap. If you are inserting an "NPN zener" you can do it any place where the "cathode/collector" is more positive than the "anode/emitter".

It happens to be easiest and most practical to insert it between the signal ground and the center tap, for safety reasons.Connect the centertap to the emitter. Connect the collector/zener to power ground.

Notice that the center tap MUST NOT GO TO ANY OTHER POINT EXCEPT THE EMITTER/ANODE. If the centertap is also connected to ground some other place, the NPN/zener is effectively shorted and does no good.

The question about whether a bipolar transistor is fried is one reason I prefer MOSFETs.

[Satamax]

Thanks a lot RG!

Well, i was searching hard! And trying to understand! You explained well, thanks a lot.

I've found thanks to Josh Powel at AX84 the old schemo from Aiken

http://web.archive.org/web/200201060...com/Zener2.PDF Which confirmed what i thought! I had it all reversed!

Thanks again.

Max.

[Marc]

the original schemo...

Here's the schematic I sent to Randall Aiken back in the AMPAGE days. He updated and made it much nicer. I copied it from and electronics Circuit encyclopedia that used to be in our local library.

http://members.aol.com/fyrebottle/sc...s/powerzen.jpg

Marc

[Satamax]

Yeehah!

It's working, went down from 457 to 412 and i've got Fivre 6V6GT stuffed in there biassed at 22mA. But it's still real loud! I have 5.33Ω load. Not double as it should be, but it's my homemade wickercab.

I'll make it sweat tomorow. Wasn't Billy Gibbons using a BF deluxe at some point???

Thanks a lot for your help guys!

Bye.

Max.

[Satamax]

Hi everybody.

I'm back with that old trick. Just to ask, how much can i drop with that BU 806? I gonna try to check power disipation of it now, but i'm daft and like to compare numbers.

Thanks a lot.

Max.


Well just edit. If i've understood correctly, BU806 can dissipate 20 watts maximum? So 150V on an amp pulling 230mA doesn't work? Uh, i'm daft? They say 200V colector emiter voltage, and 8 amps on the colector. But i'm not knowledgeable enough about transistors tu understand all that http://www.fairchildsemi.com/ds/BU/BU807.pdf

[Satamax]

Nother daft question, can it be inserted between bridge rectifier and ground?

[Satamax]

Big up! Guys, what determins the power of a transistor? Base to emiter, colector to emiter, base to colector current? I understand fcuk all to solid state, i've peeled my eyes on some sites, but to no avail for the moment.