Centre tap with Zeneers, how much drop?

[azatplayer]

Im changing my liverpool back to the rocket it was, and im gonna try the higher taps, see how it feels. If i was to need to drop B+ a little, what can i expect using zeneer's in the centre tap? And what should i use?
I have no exp with zeneers whatsoever, do they run hot?
Cheers Don

[Structo]

Zener

[billyz]

My experience was that using 5 ea 10v zeners to drop 50 volts in a Fender Concert 4x10 was that they got very HOT. I ended up using a Terminal strip to get them up off away from the chassis. And to get a little more air around them. Working well today . He says it is the best sounding Harp amp ever. I did some tube swaps to the preamp a 12at7 in the V1 possibly PI ( don't recall). I soldered the terminal strip to the chassis, so as not to drill holes. Looks neat and almost original. The terminal strip might provide some heat sinking.

I also had to rewire the bias supply to maintain the 50 volts needed to bias. Not a big deal. This was in a 6g12 circuit, so the bias was a separate tap off the secondary. I just tapped the the B+ instead.

[tubeswell]

+1 what billyz said about how to mount 'em. I also use tag strips with 5W zeners. Keep them off the chassis and the tag terminals help to radiate heat. Better still, a copper penny with a hole drilled in the centre and slipped and soldered over each lead end provides good heat sink too. If you are going to go for a chassis mount zener, you have to get much higher rated power handling, because of all the heat they pick up from the chassis, and you are pretty much only limited to 1 zener - whereas with 5W axial zeners, you can string them together in series to add up the desired voltage drop (and in this way you can increase their overall power-handling as well). I typically use any combination of 5W 9V, 12V or 15V zeners.

[Structo]

I just used a large stud mount zener mounted on the chassis floor.
The one I used was a 25 w 30v zener.

Use heat sink compound and also bypass the zener with a .01 uF ceramic.

[ChrisM]

I just used a large stud mount zener mounted on the chassis floor.
The one I used was a 25 w 30v zener.

Use heat sink compound and also bypass the zener with a .01 uF ceramic.

What do you mean by a large stud? I imagine that is like a Zener heatsink.

Do you happen to have a pic?

[Structo]

[img:381:332]http://www.af4k.com/imag/ham/1N2982.jpg[/img]

[jaysg]

The drop will be in the ball park of the zener value. It won't be exact because you're going to change your bias, which moves it around.

[M Fowler]

Just make sure the stud Zener is reverse anode to chassis. AK designation for NTE.

[talbany]

FWIW.. If your dropping 50v from a Rocket/Liverpool style 4 EL-84 amp the power raring needs to be at least 7.5 watts..

Tony

[azatplayer]

Well ive done the conversion back, with the 5199PT using the higher taps, i have WAY too much voltage. My Maz sr used 290V primary, so i would not have thought 300 too far off. Anyway it had 370V on the plates using a GZ34.

I subbed in a 5U4GB, and got down to 350V. Sounded HEAPS better at that voltage, but i reckon it needs to be closer to 335-340 and using the GZ34.

So thats about a 35V drop i need to get.
Man it had some serious sizzle at 370V, but not lot of sustain or character really.
I also tried a 500R drop on the screens aka Maz, but that only drove the plates higher. Will try it again later.
The circuit is all rocket, apart from using a 47uf in the first stage, and that only for the sake of the 5U4G.

So, gotta get me some Zeners!

[tubeswell]

4 x 9V 5W in series oughta do it

[azatplayer]

Well all the shop had was 5 watt 12V in stock. I tied 3 together and puyt them in place, dropped too much! SO I pulled one, and im bang on 330V where i wanted to be with the GZ34. Perfect, and it sounds pretty damn close. Just gotta tweak the dropping string a little. also a tad bassy, and i might put the bright switch in from the express.
Is it worth filling the extra hole from the pool build with a mid pot?

[stiltamp]

Have a look to this page:
http://www.geofex.com/Article_Folders/m ... tfolly.htm
Scroll down to the end of the page.
There is a power zener replacement circuit by an Power Mosfet, a zener and two resistors shown.
So you can save the power zeners.

[azatplayer]

Quick question, as im running higher voltages now, curious on what others have done in the dropping string. Have you kept the preamp voltages same? or allowed them to run higher?