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In Reply to: RE: RAPHAELITE Sinovt 2A3-845 MonoBlock acting up posted by DAK on April 12, 2016 at 13:49:27
When you say "now they are not working right..." do you mean that they did until recently?
You said the fuse-blowing amp sort of worked at 80vAC - I assume this was the power input from a variac? And it was designed for 110 volts. Presumably it blows fuses at 120v or whatever you have. Does it blow fuses at 110v input? Are you using slow-blow fuses or fast-blow?
Without a schematic, I have no way to evaluate the voltages, except for the 2A3. It seems to be cathode biased, so the filament voltage will be that between pins 1 and 4 (the slightly larger ones). At 80vAC power line, the 2A3 voltages indicate the standard operating point from the RCA manual. It is disturbing to see such a close match with the specification, given that the input voltage was only 73% of the presumed design target.
I see no point in addressing the distorting amp until the fuse-blowing amp is functional. Only then can we compare voltages between the two amps, which might enable a diagnosis.
Follow Ups:
Hi Paul, on the 2a3 I measured 45vdc more or less, on 3 pins of the tube. Is this normal bias voltage, more or less. I have no experience with 2a3s so any advice is welcome. regards, Dak
The 2A3 bias voltage is 45 volts at the most standard operating point - see the link for a typical data sheet.
What is called the filament voltage is applied across the filament, measured with one meter probe on pin 1 and the other on pin 4. Really, there is no such thing as a voltage; there are only voltage differences. Usually but nowhere near always, one of the probes is on the ground - but even then, sometimes you also need to choose between signal ground, power supply ground, and safety ground.
OK, thank you for the info. The fact that I measured +45 vdc is not a problem? Also I could not find the cathode resistor. On this amp they also take the heater wires to the interstage tranny. What is the purpose of that? thanx again, Dak
And it was designed for 110 volts
Paul that is exactly what I told him over on DIY audio.Usually the one's bought on Ebay were halved from the 220vac that China uses and what I ended up doing was series connecting 450v electrolytics as they were swelled and then I changed the supply resistor to a higher value feeding the driver and preamp tubes as the B+ was 34v high..The outputs were higher as well but I didn't worry about it as much especially since the 845s could handle much more than the 720v the Music Angel was feeding them.
They should have designed a power transformer that was for the US and Canadian markets.
A friend you get for nothing,an enemy has to be bought
Yes, they were working until a few months ago.
I have not run the AC voltage up to full yet.
The fuse I am currently using is a fast blo.
It is good to know that the 2a3 is working properly.
I will be attempting full voltage on this amp and then get some voltage readings. thank you for the confirmation. regards, Dak
Dak
Did you get the email off to them?
A friend you get for nothing,an enemy has to be bought
The link you gave was not actually the manufacturer. It is like a clearinghouse for contacting various manufacturers. Anyway, I went through the motions and filled out the contact info, but no word so far.
The amp was actually purchased on Amazon. Evidently there is no warranty left. And the seller is also being scarce. So, I am afraid i will just have to try and sort this myself and hopefully you all can help too. cheers, Dak
I asked ebay seller "listeningchina.hifi.cn" if there was a schematic.
This was his response.
"hi,sorry the schematic is available for the buyer who purchased this item."
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
So, this ebay seller has the Sinovt 2a3 845? The amp comes from Amazon though. so do you think the seller would give me the schematic?
Yes. He has them listed at the link below.
I don't think he would give a schematic to anyone except the one that buys the amps from him.
But it is good to know that there is a schematic for that amp.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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