Siemens U273B - Recap
« on: May 20, 2020, 03:50:17 PM »
I got an old Siemens U273B and I've been asked to recap the unit.
Since the unit has mounted in an external enclosure, I would like to save time on disassemble it and reassemble again before starting to replace the old capacitors so I'm looking for a schematic of the U273B so I'll know what capacitors to order.
Does someone have this schematic?
« Last Edit: May 21, 2020, 07:07:06 AM by smilan »


mjrippe

Re: Siemens u273b - Schematic Needed
« Reply #1 on: May 20, 2020, 03:56:02 PM »
http://audio.kubarth.com/rundfunk/index.cgi

For all your German module needs!

Re: Siemens u273b - Schematic Needed
« Reply #2 on: May 20, 2020, 06:30:18 PM »
Thanks, I found it

Re: Siemens u273b - Schematic Needed
« Reply #3 on: May 21, 2020, 07:06:36 AM »
After looking at the schematic and the U273B PCB I see that all of t he following caps are tantalum C3, C7, C8, C9, C15, C19, C21, C22, C23, C24.
https://i.ibb.co/Pz5vXCD/u273b-page-001.jpg

Would you recommend on direct replacement with new tantalum caps or it's better to use low  Z aluminum caps?

mjrippe

Re: Siemens U273B - Recap
« Reply #4 on: May 21, 2020, 01:35:41 PM »
Unless they are on the voltage rails or clearly dead, I would leave them alone.  If on power rails, replace with low z electrolytics for sure.

Re: Siemens U273B - Recap
« Reply #5 on: May 22, 2020, 04:05:08 PM »
The more I'm looking on this schematic I see that I don't really understand how this circuit works.
If someone is willing to explain it to me I'll be grateful.

PRR

Re: Siemens U273B - Recap
« Reply #6 on: May 23, 2020, 12:27:38 AM »
> I don't really understand how this circuit works. If someone is willing to explain it

Surely you can explain some of it. TR1 TR2 are power smoothers? T3 is the output transformer? So Tr5 Tr4 Tr3 Tr7 are likely a push-pull NFB amplifier to drive the output? Tr12 drives a meter, Tr6 Tr8 seem to short-out the signal, so Tr10 may be a control voltage buffer?

Re: Siemens U273B - Recap
« Reply #7 on: May 23, 2020, 07:07:27 AM »
Thanks PRR!
So we can say that T4 is a buffer stage, TR11 and TR13 works as a peak amplifiers for positive and negative halves of the signal, and the peaks being send to input stage as a negative feedback that reducing the gain of the louder parts of the input signal?


 

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