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separate rectifiers for input and output stages?

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Posted on April 14, 2017 at 11:05:32
floydandrews
Audiophile

Posts: 318
Location: Port Townsend, WA
Joined: December 29, 2003
 Is there an advantage to using a separate tube rectifier for the input stage of a SE amp (shared transformer but separate rectifiers and PS), compared to the usual practice of 1 rectifier and the input stage PS connection "downstream" of the output stage connection? How about compared to a shared transformer but separate rectifiers and PS for each channel? I tried a search but found little on the subject.Perhaps my search terms were too vague. The power transformer is a Hammond 278CX, and I have a separate 18A filament transformer, so having enough current for extra filaments is not an issue.

 

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was quite commonly done from early 50's to early 60's in better designs.~nT, posted on April 14, 2017 at 11:27:53
Cleantimestream
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Posts: 7550
Location: Kentucky
Joined: June 30, 2005
 ~!
The Mind has No Firewall~ U.S. Army War College.

 

RE: separate rectifiers for input and output stages? , posted on April 14, 2017 at 12:30:57
SteveBrown
Audiophile

Posts: 2454
Location: Portland, OR
Joined: November 14, 2002
 I have done this before and really liked it for one main reason - tweaking. A separate power supply for both sections allows you to more easily adjust each without impacting the other. For example, you want to listen to the effect of 10 more ma on the output. In other designs that extra current draw is also going to impact the front end of the design, and vice versa. You can also more easily try completely different drives up front, etc. Downside is, of course, likely needing a custom wound transformer. With companies like Hybore, that is a lot more economically feasible now. If you use a bias supply, I'd add another winding for that one as well.

 

RE: separate rectifiers for input and output stages? , posted on April 15, 2017 at 14:54:11
Triode_Kingdom
Audiophile

Posts: 10044
Location: Central Texas
Joined: September 24, 2006
 "I have a separate 18A filament transformer, so having enough current for extra filaments is not an issue."

Just FYI - Filament transformers are rated for output voltage under full load. Using a large transformer like this to power, say, 2A or 3A of filaments will probably over-voltage the tubes.



 

RE: separate rectifiers for input and output stages? , posted on April 15, 2017 at 20:46:37
floydandrews
Audiophile

Posts: 318
Location: Port Townsend, WA
Joined: December 29, 2003
 I was aware of that, but it never hurts to be reminded. The filament transformer has multiple input taps, which can be used to keep the output voltage at 6.3V under load.

 

Even DC heating on the input tube of my 'once were LEAK St20s' helps with quietness., posted on April 18, 2017 at 15:23:29
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
 Used the 5V tap for the valve rectifier, which we did not use.

Can't recall how we fudged it to 6.3V, and DC'd it. But it sure worked well.


Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

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