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Re: Super Rvb. Choke?


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1/23/2003 10:35 PM
Denny
Re: Super Rvb. Choke?
Any suggestions for a Super Rvb. type amp? My amp is actually a late 60's or early 70's Bassman 10 that I've blackfaced the power section, other than I still have the 7watt wirewound resistor in place instead of a choke. The only spec I see on the replacement choke for a Super Rvb. is 90mA DC. Any help would be greatly appreciated.  
Denny
 
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1/28/2003 12:15 PM
John Kelley Brown

Fender used 3 henry chokes. But you can play around with this for tone, try chokes like 3h then up from that, you might like the 12h Hammond 193B or even the 20h 193C, messing with this stuff is where all the fun is. :)  
Kelley
 
2/26/2003 8:47 AM
Jani Koskelainen
Re: choke inductance calculation
I have very old book called 'Low frequency amplification' which is some sort of a tube amp bible (written in '50 era).  
 
It says that coil inductance must be big enough to maintain current through whole cycle. Otherwise it would need to build magnetism every time rectified pulse comes from supply and cause significant voltage drop.  
 
It had a page of fourier analysis, and result formula for 50Hz mains frequency was (full wave rectified):  
 
L >/= (Rload/1000) H  
 
Rload is in ohms (The formula is 'as i remember it' so there is possibility for error, but i will correct it after i have checked it from the book..)  
 
There was also a mention that coil should splitted so, that first coil would be without air gap and, after capacitor, second coil would be with air gap.  
 
Then first coil would be 'adjusting' with DC load (Seen as Rload) due to saturation of core and let supply adapt itself to amplifier load.  
 
-Jani-
 
2/27/2003 11:15 AM
Jani Koskelainen
Checked.. it was just like that
So,  
 
minimum value for inductance:  
 
L=Rload/1000 (Henries)  
 
or  
 
Usupply/(1000 x Isupply)  
 
U and I in volts and amps, then L comes in henries  
 
Inductor splitting was due to fact that when load becomes smaller, it is harder to to keep inductor current running, and that's where core saturation helps.. second inductor gives rest of smoothing effect  
 
-jani-
 

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