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Maximo Chokee!!

8/21/1999 1:44 AM
Maximo Chokee!!
What type/brand of Choke supplies the MOST  
amount of voltage drop?  
Using Hammond PT (300-0-300 at 150mA) with 2xEL84s.  
Now, I have 392V on the plates of those EL84s, so, I want a *large* choke value.  
I'm also going to install a Zener to lower the voltages, too.  
8/21/1999 12:40 PM

Hi, Mook. Are you using a choke input filter on the power supply? That will drop the voltage. Other than that, maybe get one with a massive DC resistance that will handle your current? I have a few 40 henry chokes here, you bet they have some DCR, several hundred ohms.
8/21/1999 7:10 PM

But how do I pick a choke?? Never done that before.  
For max voltage drop, do I go for the largest Henry rating or the most resistance?  
Most chokes don't have a resistance over 1K. Why not use a larger resistor, instead???  
And what about the mA rating of the choke - do I select one with the largest amperage? Or, must I pick a choke with a mA rating UNDER that of my PT?  
8/21/1999 7:55 PM
Mook, go here:  
and read about choke input supplies. There's a lot of neat features that you don't get in cap inputs.  
This article should help answer at least SOME of your questions.  
8/22/1999 1:11 AM
Steve A.

    I browsed through that article a bit (there's much to study later!) and the "choke input filter" sounds exactly like the chokes that Fender, et al, have used in guitar amps. So what is the difference? (I guess that article is intended more for the tube hi-fi crowd, who apparently don't take kindly to chokes...)  
Thanks for the link!  
Steve Ahola
8/22/1999 2:39 AM
Michael Cameron
Fender never used Choke input filters. They used Cap input filters. The choke was between the caps not in front... The RCA tube manuals have a good description and diagram of the various filters if you need to see it. Most of the Fender amps that used a choke used it after the plates, so that it only filtered the screens of the power tubes and the PI and preamp further down the chain. This saved them some bucks by not having to source a choke with as large a crrrent rating.  
8/22/1999 7:29 AM
Steve A.

    Thanks for your explanation! So "choke input filters" and "cap input filters" would be mutually exclusive? (Only one of them could come first in the power supply- right?)  
    I can see how a big hefty choke ahead of the filter caps and plates could drop the B+ voltage quite a bit. So how do they respond to playing dynamics? Like if you hit a hard, loud note does the voltage sag a bit or is it more stabilized?  
Steve Ahola
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