Hi,
So I am following up from a recent stereo tube amp design that was not working and right now I am working on the power supply. Please look at the picture below as well as the schematic. When I add power to the transformer it hums louder increasingly and beings smoking which is a sign something is not connected right. Please advise, thanks!
So I am following up from a recent stereo tube amp design that was not working and right now I am working on the power supply. Please look at the picture below as well as the schematic. When I add power to the transformer it hums louder increasingly and beings smoking which is a sign something is not connected right. Please advise, thanks!
The 1N4007 look under rated to me. If you have 350 vrms and 490 volts peak then each diode sees effectively 1000 volts across it. The cap needs to be rated at closer to 600 volt to cope with no loading.
The diagram is fine electrically, text book full wave rectifier. If its not happy then something is breaking down.
The diagram is fine electrically, text book full wave rectifier. If its not happy then something is breaking down.
Well for one thing, you’re going to draw about half an amp with a 1k load
I appears your center tap (red and yellow) is connected to one of the diodes, and one of the solid red leads is taken to the negative lead of the cap, which results in a direct short. The red with yellow goes to the negative side of the cap, and each solid red goes to a diode.
...and then have a fire extinguisher ready. Use a long extension cord for the plug-in step.
My immediate thought (after the shock of looking at the picture the OP bravely posted) was that the bleeder resistor needs to be 100k instead...
The 273BX can do around 200mA, but with cap input you need to cut that down to 2/3 so maybe 133mA. Not sure what load the OP wants to use this for, but a bleeder resistor is always good practice. I will give them credit for doing that. Just not one which is such a low value.
With a 1k bleeder, that circuit is drawing around well over 400mA so no surprise the OP's 273BX is smokin'. Sad to waste an otherwise good power transformer that way.
Let's think about 5mA for the bleeder resistor instead. Wow, that's around 100k ohm... I guess my maths still work. The voltage is going to be 526V with no load, so that 400V input cap is not going to cut it with a 100K ohm bleeder. Ha, it doesn't cut it with a 1K bleeder either, wonder why the 400V input cap didn't pop (yet).
And yeah, the PIV on the 1N4007's is going to be exceeded. There is a very simple solution for this. But we have no idea what the real load is because the OP didn't post the circuit. It could very well be that this power transformer won't fill the bill in any case.
Maybe the OP could look at other builds, how people do them and safety and stuff? Just an idea.
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So I have done this fix and changed my diodes to the 10A10A type which is rated for 1000V, 10A. The problem is still there! As some of the good folks here mentioned ealier, it looks like I need a capacitor rated for 600v Atleast... I'll be posting as I get new findings
the red/with yellow stripe wire is the CT, it goes to ground, the minus of the caps and the return of your load.
each red wire each goes separately to the black end of a diode, then both diodes outputs are jointed at the capacitor +.
then the + goes to your load, as others mentioned try placing a very high R and measure the current and voltages.
also the primary is important, ONLY wire the + and zero to the transformer primary black and gray usually.
The ground (third wire) should be grounding with the CT. Measure that too that there is no current going there
Use a variac, and please clean your setup, it looks very confused.
each red wire each goes separately to the black end of a diode, then both diodes outputs are jointed at the capacitor +.
then the + goes to your load, as others mentioned try placing a very high R and measure the current and voltages.
also the primary is important, ONLY wire the + and zero to the transformer primary black and gray usually.
The ground (third wire) should be grounding with the CT. Measure that too that there is no current going there
Use a variac, and please clean your setup, it looks very confused.
I would not build anything with that transformer, the smoke you saw unfortunately is generated by varnish insulation burning on the windings, if it does not already have a shorted winding, it is likely to develop one or more in the future. It could also be quite hazardous if it develops a winding to core short.
Yes Kevin!, maybe it survived^.^ for precaution check insulation with ohmmeter and ground the transformer case to safety ground. Measure the current if there is any also!
A variac would have prevented this, I wired like that by mistake and the variac saved the day.
A variac would have prevented this, I wired like that by mistake and the variac saved the day.
The problem is that the insulation is damaged, even if it has not failed to this point in time electrical stress and heating in normal use will further degrade the insulation over time. I would consider it compromised, maybe has some short term use on the bench. I have replaced a lot of power transformers that were not misapplied, but nonetheless failed over time. Way back when I serviced tube amps for a living I occasionally scrapped an amp that had a fried power transformer because economic replacements were not available unfortunately.
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I'm with Kevin. As I posted before, it's sad to waste an otherwise good power transformer that way.
Also, it doesn't appear that the OP bothered to read my post, or they would have further revised their circuit. Seriously, I can't tell anything from the picture that is posted. For me, this is a strong indication of poor construction practices. I hope the OP survives.
Also, it doesn't appear that the OP bothered to read my post, or they would have further revised their circuit. Seriously, I can't tell anything from the picture that is posted. For me, this is a strong indication of poor construction practices. I hope the OP survives.
Have you addressed the loading. At the very least don’t power up the transformer again without a proper load. 1 K allows too much current