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Rosscopecotrain 7th August 2011 09:50 PM

Rotel RB-1010 power amp varistor!
Hi all!

I have recently purchased a rotel RB-1010 power amplifier and have been trying to source some new varistors (Sanken SV-04S) {old ones not working}. unfortunately I have not had much luck and it seems that they are unobtainable. I just wondered if anybody had any ideas as to where I might source these or a similar varistor that would do the job!

Any help would be greatly appreciated!

Many thanks!


gmphadte 8th August 2011 04:44 AM

Is it connected across the mains input?

homemodder 8th August 2011 10:37 AM

You should be able to find a service dealer in the uk, they usually keep or can order replacement parts otherwise go here B&W Group North America Service & Support Homepage and choose the parts centre.

Rosscopecotrain 8th August 2011 07:55 PM

Hi folks!

It is not connected across the mains or anywhere near to the mains transformer! unfortunately I have no idea what it is supposed to do or why it is connected to the main heatsinks of the amplifier! On the circuit diagrams it is just shown as 4 diodes in a row! I have visited the B&W website and also rang there service centre! they were very helpful but could not supply me with the parts that I needed. I have been trying to source this part for a long time and cannot find much if any information as to what it is and where I can find a replacement. Its proving to be a massive headache!

A service manual for the amplifier can be found at the above mentioned site and the information on the part I am looking for can be found at the website stated below:-

SV04S datasheet and application note, data sheet, circuit, pdf, cross reference, pinout | Datasheet Archive

If anybody more experienced than myself wants to take a look at the circuit diagram and shed a light on what this varistor does and how and what I can do to replace it! it would be much appreciated!

Thanks again to those that have replyed to the post and hope that the information above will be of some assistance!

cheers! Ross

burbeck 8th August 2011 10:01 PM

hi Ross
the SV04S is not a varistor (although Rotel call them that in the service manual)
these devices are 3 series connected silicone diodes in one package specially made for bias control in amplifiers they are temperature sensitive and are very often mounted on the out put transistors or heatsink. the allows the bias of the output stage to track with temperature.

are you sure that they have blown, test them as 3 series connected silicone diodes, volt drop will be about 2 volts @10ma test current. if they are blown it is very likely that there will be more damage in the output and driver stages.

as a substitute use 3 ordinary silicone diodes connected in series, thes have to be thermaly in contact with the heat sink, but electrically isolated from it.

i always subtitute the diodes first without putting in contact with the heat sink. just to get the amp up and running, it will work this way as a test.
a tip after the amp is running i use thermal bonding glue to fix them.
diodes i use are 1n4002 or similar.


Rosscopecotrain 9th August 2011 11:00 PM

Hi Bob!

Thanks for the reply and suggestion It looks like making my own may be the only option! The amplifier itself has been tampered with quite a bit by the previous owner and was described on ebay as being inoperative on one channel. When I opened the unit I found alot of damage had been caused; PCB track lifted, broken and missing and one cicuit board had even been snapped in half and glued back togeather. The previous owner had replaced output and driver transistors on one side of the amplifier as well. The diodes that I have described which are linked to the heatsinks of the main amplifier and the smaller driver transistor on the same channel are not the originals and have been made by the previous owner to replace the old units! These are the ones that I would like to replace as I have tested them and they are both totally dead. I have replaced quite a few components myself including output and driver transistors and all components which were linked to them but all the components that I have taken out have tested fine and don't appear to be faulty in any way. Being that they all tested correctly and the home made diodes did not! Do you think that these are what is stopping the one channel from working? Also with regard to making diodes myself how would I connect them to the heatsink properly and where could I get the glue needed to insulate them?

Cheers and Thanks again Bob!


burbeck 10th August 2011 07:14 AM

hi Ross
this is quite a complex amp to cut your teeth on, the diodes are esential for the amp to work as they provide the bias voltage for the output stage.

how did you test them? i would use a 9 volt battery in series with a 680 ohm resistor across them, this is roughly 10mA, measure the voltage across the diode string should be around 2v. out of circuit of course.

with so many parts blown in the output stage i would test all the semi conductors, transistors and diodes before applying power. work methodicaly through the whole board, one by one. if in dout compare with good channel part etc.

not knowing your level of competence or the equipment availible to you it is hard to give more advise, if you dont understand what i have said above maby stop there. safety first.

however when you think the amp is ready to test use a mains light bulb in series with the mains to limit the current in case of another fault, be very carfull with this conection safety first. on switch on the bulb will light brightly for a second or two then dim down.

the adesive is here Buy PCB Compounds and Adhesives Thermal bonding epoxy adhesive,20ml Electrolube ERTBS20S online from RS for next day delivery.

Rosscopecotrain 10th August 2011 10:05 PM

Hi bob!

Thanks again for your reply!

I do have some experience with electronics and know how to perform basic tests with a multimeter on components! but as for performing tests in the way you desribed or any circuit testing it is all pretty new stuff to me.

If you could provide diagrams of the tests you are describing it would be a great help as I work more effectively when I have a picture reference to apply the written knowledge to!

As far as test equipment goes I have an amprobe multimeter which tests all the basic things such as resistance and capacitance and also AC and DC voltages.

The diode strings in the amplifier number 4 diodes in series! I wondered if the 3 diode strings that you had described in the last post would be suitable or would I have to use four as per the originals!

Hope this answers some of your questions and again thanks for you help! it is very much appreciated! If it werent for people like yourself I would be very stuck indeed!

Cheers! Ross!

Rosscopecotrain 10th August 2011 10:19 PM

Hi bob!

Forgot to post this on the last message!

I tested the diodes with a multimeter on the diode setting with the correct polarity and they didnt even register! this is why I believe them to be defunkt!
Are they suppose to behave in a different way to a singular diode with regards to testing or is my prognosis correct??

Cheers! and thanks again! Ross!

burbeck 11th August 2011 04:52 PM

hi again
sorry i meant 4 diodes not 3.

yes they are four diodes in series and might not measure anything on the diode test function on the meter you have, i would expect the voltage drop to be around 2.8 volts. i would test these as described.

connect the diode in series with a 9v battery and a 680 ohm resistor, then measure the volt drop across the diode. for this test the diode must be the correct way round, ie anode to the + terminal of the battery.

the resistor ensures that about 10ma flows in the diode string

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