An audio buddy bought this raphaelite sinovt 2a3-845 single ended amp just a few months and has already run into problems. I am looking for a schematic.
One amp blows fuses while the other has weak distorted sound. Ok, the weak one might be tubes so I will check that out first. But the one that blows fuses sounds serious. I opened it up and at first look have not found anything incriminating. Both of these are tube rectified so I will also check that out. TIA, 808
One amp blows fuses while the other has weak distorted sound. Ok, the weak one might be tubes so I will check that out first. But the one that blows fuses sounds serious. I opened it up and at first look have not found anything incriminating. Both of these are tube rectified so I will also check that out. TIA, 808
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The biggest problem on the Chinese amps if they were bought off Ebay is many were just a halved conversion of the 220vac line that they use in China.
It's not unusual for them to tap the line as opposed to put in a power trafo wound for 122vac 60cps for the US market..
I did a pair of Music Angel 845 Int amps and they ran hot for this very reason..They were wired for 110vac and the input supply filter caps swelled from over voltage so I put in a pair 400vdc caps in series with balancing resistors as well and I had to add a resistor to the B+ supply that fed the driver section.
Ask if your friend bought them on Ebay and if he did,look at the input AC setup.Here is the contact info for Sinovt and they should email you a schematic. Contact Us - Sinovt Vavle Amplifier Co. Ltd
I did trace out the circuit but still big question marks about the power supply where I suspect the problems lie.
The input has SE and Balanced connectors. The input goes to an input transformer then to a 12at7. This is cap coupled to the 2a3 driver which is transformer coupled to the 845 tube. No problems apparent in this area.
So, this pretty much leaves the power supply. So, it would be nice to have the schematic for the stock voltages on the PS.
The heater supply for the 2a3 and the 845 are both rectified. and also voltages for the various stages are a mystery. It doesn't look like there is any type of voltage regulation as I did not notice any transistors but who knows what lurks under the circuit boards? If anyone has some other places to check please let me know, cheers, 808
Post a picture of it and maybe we can see something obvious..Do you still have your MAC MC240? I did pick up 250 NOS cinch sockets for the Mc240,Mc225,Citation 2s and Citation 5s..
HI Mike, I think that contact site might be for some other company. Anyway, I put in an email request so maybe it will go somewhere, but I am not holding my breath.
Anyway, I opened up the amp and just as you said the power transformer is tapped at 110 and 220. I have not tried to test the amp at full power yet. I will try and see what happens.
sorry about all the smiley faces, my granddaughter made me do it.
They're so nice ! The officer one is reserved for the moderators onlymaybe too late? but i have the diagram for the 845 and the 805,(it is the same diagram as the already build version because i wanted to build the kit version (wooden front panels) but it is now more than a year and got no response, i bought 4 years ago the csm30 kit (with the glow disharge stabiliser tubes). But now it seems that they are terrible with customs services because i got no response on several email adresses from them....
I would add that you can always put a sine wave into the input jacks (even from your phone) and look at what comes out of each stage on a scope.
If you don't have a scope, use 60Hz and measure the AC voltage with your meter. You should get 20-50x the input voltage out of the 12AT7 stage, about 2-4x more from the 2A3, and a hair more from the 845 itself. The interstage transformer is a bit of a wild card, but look for consistency between amps. Measuring the AC output of the 845 stage is not generally reasonable for most meters people have on the shelf, so you'll want to measure the DC resistance of the primary and secondary windings of both output transformers (again, look for consistency), then look at the AC voltage available on the secondary.
The rectified filaments for the 2A3 should read about 2.5V DC (wouldn't be surprised if it reads a little low if it's just the AC winding feeding a bridge with a cap soldered to it). The 845 should show about 10V on its filaments.
You may also want to post where you are in the US, there may be someone in your area who will give you an assist.
I have a pair of Shuguang 845 monoblocks that were not operational when I received them in trade. I had a pair of larger power transformers wound for them by Heyboer in the US and ditched the heat trapping transformer shrouds.
If you don't have a scope, use 60Hz and measure the AC voltage with your meter. You should get 20-50x the input voltage out of the 12AT7 stage, about 2-4x more from the 2A3, and a hair more from the 845 itself. The interstage transformer is a bit of a wild card, but look for consistency between amps. Measuring the AC output of the 845 stage is not generally reasonable for most meters people have on the shelf, so you'll want to measure the DC resistance of the primary and secondary windings of both output transformers (again, look for consistency), then look at the AC voltage available on the secondary.
The rectified filaments for the 2A3 should read about 2.5V DC (wouldn't be surprised if it reads a little low if it's just the AC winding feeding a bridge with a cap soldered to it). The 845 should show about 10V on its filaments.
You may also want to post where you are in the US, there may be someone in your area who will give you an assist.
I have a pair of Shuguang 845 monoblocks that were not operational when I received them in trade. I had a pair of larger power transformers wound for them by Heyboer in the US and ditched the heat trapping transformer shrouds.
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What is your problem? In the unit that i repaired, the pot for the negative bias voltage was defective. I also changed the amp to running 211 tubes. I also had the owner run his amp thru a variac which outputted 110vac . This made everything run at the proper voltages. Running the amp at 120vac was eating up the 845 power tubes after only a few months.
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