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Old 10th September 2007, 06:00 AM   #1
tyor is offline tyor  Norway
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Default PSU problem

I am building a psu for a 250TH SE amp. I have a transformer that gives 1040v ac Planning tu use hybrid rectifier. (tubes and SS) So I dont have to use 4 heater vindings. But kan I conect the fillaments on the pic in serie? The transformer has 1x5v for heaters and i plan to use 866 tubes ratet for 2.5v fillament.
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Old 10th September 2007, 07:04 AM   #2
Colt45 is offline Colt45  Serbia
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should be ok, but make sure to take B+ from pin 4 ( if i remember, the one with the shield). so tie both pin 4 together.

better to use a 5v CT trafo though, incase slight unbalance in heater current, probably.

I don't know if i'd bother with 866's, they look nice but they're a pain in the ***.


I don't really see the point of this half silicon ****.. all or nothing!
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Old 10th September 2007, 07:13 AM   #3
tyor is offline tyor  Norway
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I planned to use 4x866 but I have to use 3 seperate fillament vindings that can stand the high voltage. In this way I can use the one fillament vinding on the transformator, and still have the blue light
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Old 10th September 2007, 09:36 AM   #4
Colt45 is offline Colt45  Serbia
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I'm not sure how you'll switch this then, with integrated 5v winding. You'll have to switch the HT... because 866 needs a long warmup.
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Old 10th September 2007, 11:44 AM   #5
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Series filaments on 5V will work fine, but listen to Colt45. MV rectifiers need to heat up for half a minute before B+ is applied. You could use a separate filament supply with a separate power switch. Some people have used a single transformer and put a standby switch in one of the HV secondary leads, though 1000VAC on a switch scares me. A solution that I like is to put a single damper diode in series after the bridge. It takes 30 seconds or so to warm up, then provides a soft start. You can put a switch across the damper to short it once everything is warmed up and running.
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Old 10th September 2007, 06:40 PM   #6
tyor is offline tyor  Norway
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Thanks for al the tips. But I have decided to revind a toriod trafo to 2.5V sek.
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Old 11th September 2007, 03:00 AM   #7
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" A solution that I like is to put a single damper diode in series after the bridge. It takes 30 seconds or so to warm up, then provides a soft start. You can put a switch across the damper to short it once everything is warmed up and running. "

Hi Dave ,

Wow !!!! Really a very , very good idea , congratulations .

I had never thought about this very simple solution !!!

Regards ,

Carlos
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