telefunken: Telefunken Opus 7 USA
ID: 84595
telefunken: Telefunken Opus 7 USA
29.Dec.05 08:50
0
Would someone out there know why the Telefunken power transformer only has 216 VAC secondary (230VAC unloaded)on the US model, but the schematics say 255VDC @110 mA for the B+ after the selenium bridge rectifier?
When my radio is powered up the reading on my radio is 233 VDC for the B+ after the selenium bridge rectifier.
Omer
When my radio is powered up the reading on my radio is 233 VDC for the B+ after the selenium bridge rectifier.
Omer
To thank the Author because you find the post helpful or well done.
Check rectifier (and electrolytics)
30.Dec.05 19:52
Hi Omer,
In theory B+ is ~ AC * 1,4142
I assume that you have checked/replaced the electrolytic and paper caps?
If the transformer and the caps are OK and B+ is too low
the selenium rectifier may be off-spec (higher internal resistance
than specified).
Selenium rectifiers are similar candidats like vacuum rectifiers
which needs to be replaced after some decades ;-)
They can additionally become ill or die by environmental influence.
If you do not find a good NOS spare part I would use four 1N4007
instead, and a resistor to drop B+ to the requirement of the circuit diagram.
The difference between AC secondary unloaded versus loaded will
increase if the rectifier is in normal condition, it depends on
the resistance of the transformers high voltage windings and the load.
Hope that helps.
Kind Regards
Georg
In theory B+ is ~ AC * 1,4142
I assume that you have checked/replaced the electrolytic and paper caps?
If the transformer and the caps are OK and B+ is too low
the selenium rectifier may be off-spec (higher internal resistance
than specified).
Selenium rectifiers are similar candidats like vacuum rectifiers
which needs to be replaced after some decades ;-)
They can additionally become ill or die by environmental influence.
If you do not find a good NOS spare part I would use four 1N4007
instead, and a resistor to drop B+ to the requirement of the circuit diagram.
The difference between AC secondary unloaded versus loaded will
increase if the rectifier is in normal condition, it depends on
the resistance of the transformers high voltage windings and the load.
Hope that helps.
Kind Regards
Georg
To thank the Author because you find the post helpful or well done.
31.Dec.05 06:59
Thanks for the reply!
The reason why I am posing this question is, the Telefunken Hannover tranformer has "216 VAC" for the secondary written on the side. How do you get from 216 VAC to 255 VDC @110mA after the rectifier, under load (the Opus 7)?
The transformer is about 227 VAC unloaded.
I definatly will go with a silicon bridge special with adequete dropping resistor, but if I'm not mistaken, Max Grundig's transformers were all about 274 VAC unloaded of this vintage, meaning that they were about +/-255 VAC loaded.
Just wondering
Omer
BTW I was able to cure the vibrating transformer by injecting , with a syringe, GC Red Insulating Varnish into the core and hammering thin wooden wedges at the top.
The reason why I am posing this question is, the Telefunken Hannover tranformer has "216 VAC" for the secondary written on the side. How do you get from 216 VAC to 255 VDC @110mA after the rectifier, under load (the Opus 7)?
The transformer is about 227 VAC unloaded.
I definatly will go with a silicon bridge special with adequete dropping resistor, but if I'm not mistaken, Max Grundig's transformers were all about 274 VAC unloaded of this vintage, meaning that they were about +/-255 VAC loaded.
Just wondering
Omer
BTW I was able to cure the vibrating transformer by injecting , with a syringe, GC Red Insulating Varnish into the core and hammering thin wooden wedges at the top.
To thank the Author because you find the post helpful or well done.