Braun SK55 | Transistor

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robinkeussen
Neuling
Neuling
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Registriert: 07.05.2014, 05:55
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Braun SK55 | Transistor

#1 Beitrag von robinkeussen » 23.05.2015, 12:17

Hi Again,

I have an issue, from one day to the next my Braun SK 55 no longer worked. I saw that the fuse was broken so i went out and bought a replacement. The new fuse blew out as soon as i turned it on. I took it to an audio repair shop to see if they could help and I was told that the Transistor is broken due to a leaking capacitor. I was told that there is no way to repair my unit.

I was hoping that someone on here would be abe to help me out, either;
A. Repair/replace the current transistor
B. Make a workaround with new components.

Any help would be greatly appreciate

I would like to contribute to this forum and have drawn the Plastic Lid and wooden sides, and the graphic for the radio bands all to scale in CAD, if someone could lead me to the right area to post for other to use.

Greeting from Sydney.
Robin

wickerge
Braun-Spezi
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Beiträge: 1167
Registriert: 26.05.2009, 21:52

Re: Braun SK55 | Transistor

#2 Beitrag von wickerge » 23.05.2015, 13:04

Hello Robin,
you should probably look for a different repair shop. There aren't any transistors inside the SK55. The only semiconductor in it is a diode for the DC-generation. Anything else is done by tubes (which are still quite easy to get). If you need a circuit diagram for the SK 55 please let me know.
Maybe the capacitor in the power supply is the problem and has killed the diode, but replacement parts for these should be easily available. You know how to use a soldering iron?

Best Regards

Gerhard

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Rainer Hebermehl
Lautsprecher-Profi
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Registriert: 29.06.2009, 13:55
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Re: Braun SK55 | Transistor

#3 Beitrag von Rainer Hebermehl » 23.05.2015, 18:11

Hallo Gerhard,

ich vermute, daß hier nicht Transistor sondern Transformator gemeint ist. Zur Not tut es ein " stinknormaler " TRafo aus irgendeinem Röhrenradio. Minimumdaten sec. : 230 Volt 100 mA und für die Heizung 6,3 Volt 2,5 A Platz ist genug im SK55 Gehäuse.

Das Schaltbild hilft ihm vielleicht weiter.

Du bist fitter in Englisch.

Grüße
Rainer
Bild
Aus dem Radio steigt der Rauch - Soll er auch.

wickerge
Braun-Spezi
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Beiträge: 1167
Registriert: 26.05.2009, 21:52

Re: Braun SK55 | Transistor

#4 Beitrag von wickerge » 23.05.2015, 18:50

Hello Robin,
Rainer was asking whether the repair shop told you the transformer is defective. That would make sense. Is that correct?

Best Regards
Gerhard

robinkeussen
Neuling
Neuling
Beiträge: 6
Registriert: 07.05.2014, 05:55
Wohnort: Sydney
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Re: Braun SK55 | Transistor

#5 Beitrag von robinkeussen » 24.05.2015, 10:04

Thank you Rainer and Gerhard for your quick reply. I will call them tomorrow and double check, my notes from the telephone conversation was Transistor, ill double check and update.

Wishing you a great sunday

robinkeussen
Neuling
Neuling
Beiträge: 6
Registriert: 07.05.2014, 05:55
Wohnort: Sydney
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Re: Braun SK55 | Transistor

#6 Beitrag von robinkeussen » 25.05.2015, 02:32

Hi,
After calling the repair shop, it is a broken transformer. Is there a way to get a replacement part or do a modern workaround to repair.

Kind regards
Robin

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Jens
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Registriert: 19.09.2009, 11:35
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Re: Braun SK55 | Transistor

#7 Beitrag von Jens » 25.05.2015, 15:45

Hello Robin,
thanks to Rainer Hebermehl you allready received the relevant information for replacement/repair as he upload the electric circuitry and informed you about the transformer key values as a minimum requirement.
Rainer Hebermehl hat geschrieben:Zur Not tut es ein " stinknormaler " TRafo aus irgendeinem Röhrenradio. Minimumdaten sec. : 230 Volt 100 mA und für die Heizung 6,3 Volt 2,5 A Platz ist genug im SK55 Gehäuse.
Even though it might be difficult to find a one by one replacement for the SK55 power transformer straight away, many of the 50-60th tube radio utilized comparable circuitry schemes with identical set of tubes. In your case an EL-84 is in place within the main stage of the radio amplifier.
You might be able to purchase a used dedicated power transformer from ebay or other sources for old staff, reflecting Rainers minimum specification.

If you prefer to purchase a new power transformer, I would suggest to take this German source into account as Jan Wüsten is well known among Tube radio/amplifier enthusiasts. I allready purchased certain capacitors and audio transformers for tube amp projects from his side (worlwide supply according to his website).
Ask Jan First - Tubes & more

The website structure is a bit odd but you'll find everything you are searching for.
There are two transformers which obviously meet the specification mentioned by Rainer. These are not originals but low power tube transformers out of current production which probably fit.

Please have a look to the screenshots (Ask Jan First) and the preselected components:
TRA200: This transformer is on the low side but within specification of Rainer (Nice price & small).
TRA0201: This is a more powerfull transformer on sec.1 (2*230V / 100mA - parallel wiring) which might be the better choice. The sec.2 heater output (6,3V / 3A) is a bit less powerfull compared to the TRA200 but still OK. If you want to be on the safe side, it is a rule of thumb to dimension the transformer output (current) by adding 50% plus as a reserve to withstand the peak amplification and stress on the long run.
Don't forget the foot brackets and screws which are necessary and not at all a cost factor.
If you contact Mr. Wüsten on his homepage (contact Sheet) he will assist you to pick the best fitting components if you ask for.

KON5650: I spotted a hint from your repair shop that the reason for the broken transformer might be related to a leaked Capacitor. To avoid the risk of further sudden death for any new transformer you should replace this one, too. The high voltage 50uF Electrolytic Filter-Capacitor within the power supply section (according to the circuitry scheme) might be the defective one they are referring to. Please have a look into your SK55 Power supply to identify the defective capacitor and compare it with my replacement suggestion on the Screen shot below (Screw-in metal dome capacitor).

One thought from my side: Even though the repair shop discovered correctly a defective power transformer, another component under risk is the audio transformer (sitting close to the speaker) which is eager to quit the job after all these years. The result would be the same - silence in the speaker... (but probably no blown fuses...)

Warning - Important!
Please take one important feeback from our side into account. For experienced members who are used to electronics and high voltage tube circuitry the repair is not complicated. If you don't have experience in that field be warned that voltage & current within a tube amp section are dangerous to life!. We are talking about 230 V DC within the power supply unit, which could deadly shock you if you touch the circuitry or misplace components. In this case we would suggest to purchase the required parts and let a dedicated repair shop do the work.

Best regards,
Jens
Dateianhänge
TRA200.JPG
TRA0201.JPG
KON5650.JPG
Don't Panic!

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