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OT - screen reg. + PS changes for old Eico Hi Fi

8/5/2003 6:45 PM
JWK
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OT - screen reg. + PS changes for old Eico Hi Fi
I got no where on the Eico forum and the Tube Asylum tweaker forum, so I thought I'd throw this out here knowing some of you mess with tube HiFi stuff.  
 
I have an old Eico ST-70 I enjoy. I tossed around lots of grandiose plans, but it's a pentode thing, OK? I realize the best thing to do is keep it on the simple and effective side.  
 
This is a stereo amp, fixed bias using two pairs of 7591 tubes. There is a dropping resistor (no choke) to the screens designed to keep at 390v at idle according to the schematic. I figure my best bang for the buck here is to put in a voltage regulation circuit using zeners and a mosfet. Good idea for HiFi or no?  
 
Next is the power supply stage for the plates. Right now it uses a 5AR4 with a 40uF cap.  
 
1. Keep the tube and change the 'lytics to something like three 15uF Nichicon radials or something comparable. No room under the chassis for Solen.  
 
2. Change to SS rectifier and put a big honking amount of uF in there.  
 
3. Change to SS rectifier and use a pi filter, like a 30uF, choke, 30uF type arrangement. Hammmond has a 1H, 300mA choke that would work well here. Resistance is 40 ohms.  
 
My wife has sensitive, somewhat damaged hearing. Something about my SS Hafler amp actually causes her to experience mild pain. Maybe it could be a high frequency, odd harmonic thing. I really don't know if a SS rectifier arrangement would do that or not.  
 
Any thoughts, opinions, info, suggestions appreciated. Thanks.  
 
John

 
Replies:
kg [QUOTE]This is a stereo amp, fixed ... -- 8/5/2003 6:58 PM