Do you really mean standby switches in the above statement?kwijabo wrote:with the standby switch OPEN, as soon as i close the power switch (turn it on) the fuse blows. i'm not even letting anything get to the cap. and, two standby switches have broken as a result
4 blown fuses later i still don't know...
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Re: 4 blown fuses later i still don't know...
Re: 4 blown fuses later i still don't know...
Yes, are you using Slo Blo fuses?
You must use Slo Blo as the in rush current to charge any caps will cause most fast acting fuses to blow.
You must use Slo Blo as the in rush current to charge any caps will cause most fast acting fuses to blow.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: 4 blown fuses later i still don't know...
Here is the diagram from Angela you posted for 270EX which is the same as the info I posted above?
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Re: 4 blown fuses later i still don't know...
Are those snipped yellow wires still sitting close to the contacts on the standby?
If it says "Vintage" on it, -it isn't.
Re: 4 blown fuses later i still don't know...
Something a friend shared with me (actually saved me once). With amp unplugged and all switches off, measured resistance across IEC or power cord terminals -hot and nuetral. Should measure open. Flip power switch on and measure again. You should see a couple ohms or so resistance. This will check mains, power switch and PT primary wiring. If you don't see a couple of ohms(+/-), with switch on, something is wrong there. If this checks good, you can disconnect standy switch, power-up (hopefully without fuse popping) and check PT secondaries, after considering all of the good advise above.
Anything in moderation...nothing to excess
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Cliff Schecht
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Re: 4 blown fuses later i still don't know...
Every time I finish building an amp, before I apply any power to anything, I Ohm out all of the PT connections to make sure they read what they should. This is a simple check that can quickly reveal problems and save one a lot of headache.
The next test I do is to hook the hot/cold up to a function generator (set at 60 Hz, max amplitude) and measure all of the voltages in the amp. Because you are using a function generator instead of the wall the available current is very small and you won't run the risk of ruining anything because the voltages are much less than wall voltage and again the current available is very small.
I've learned my function generator well now and know that it typically puts out about 6.2V RMS into the primary side of a transformer. I can then go in and measure all of the secondary voltages to make sure they are correct. For example, with 6.2V going in and a known HT of about 800V (ignoring the CT) you should see about 43V across the two HT wires (again ignoring the CT) if your transformer is wound for 115V. This is a ratio of about 7:1 so you know that when you apply your wall voltage, you should see the ~800V AC. FWIW these numbers actually come from a transformer I was measuring today that was 115V primary and 800V secondary.
Only after I do this to AT LEAST verify the connectivity of all of the secondary windings will I apply wall voltage to a transformer, and even then it's through a small value fuse so that if anything goes awry the fuse blows quickly. IMO the function generator test is more revealing test than just Ohming everything out because it gives you results which can be scaled to verify that all of the windings are intact and giving the proper voltage ratios. I especially do all of this work on used transformers of unknown status.
Another good test to run for old iron is to "cook" it for a bit. The nicest way to do this is to hook the PT up through a variac and slowly raise the voltage up to wall voltage (like 10V every few minutes). You are checking that that the transformer doesn't get anywhere past mildly warm to the touch after an hour or so of cooking. If it's too hot to touch then the PT is bad, either a short on one winding or two separate windings shorted together.
While some of this stuff may not be applicable to the OP's topic I would recommend he power his amp on through a function gen like I detailed above. This will let him measure (scaled) voltages without blowing fuses left and right.
The next test I do is to hook the hot/cold up to a function generator (set at 60 Hz, max amplitude) and measure all of the voltages in the amp. Because you are using a function generator instead of the wall the available current is very small and you won't run the risk of ruining anything because the voltages are much less than wall voltage and again the current available is very small.
I've learned my function generator well now and know that it typically puts out about 6.2V RMS into the primary side of a transformer. I can then go in and measure all of the secondary voltages to make sure they are correct. For example, with 6.2V going in and a known HT of about 800V (ignoring the CT) you should see about 43V across the two HT wires (again ignoring the CT) if your transformer is wound for 115V. This is a ratio of about 7:1 so you know that when you apply your wall voltage, you should see the ~800V AC. FWIW these numbers actually come from a transformer I was measuring today that was 115V primary and 800V secondary.
Only after I do this to AT LEAST verify the connectivity of all of the secondary windings will I apply wall voltage to a transformer, and even then it's through a small value fuse so that if anything goes awry the fuse blows quickly. IMO the function generator test is more revealing test than just Ohming everything out because it gives you results which can be scaled to verify that all of the windings are intact and giving the proper voltage ratios. I especially do all of this work on used transformers of unknown status.
Another good test to run for old iron is to "cook" it for a bit. The nicest way to do this is to hook the PT up through a variac and slowly raise the voltage up to wall voltage (like 10V every few minutes). You are checking that that the transformer doesn't get anywhere past mildly warm to the touch after an hour or so of cooking. If it's too hot to touch then the PT is bad, either a short on one winding or two separate windings shorted together.
While some of this stuff may not be applicable to the OP's topic I would recommend he power his amp on through a function gen like I detailed above. This will let him measure (scaled) voltages without blowing fuses left and right.
Cliff Schecht - Circuit P.I.
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dorrisant
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Re: 4 blown fuses later i still don't know...
If you don't mind the work or curiosity prevails, disconnect all the secondaries... Tape them all off and try it then. If it holds... turn it off and connect one set of secondaries. Repeat until you find the culprit. You will have narrowed it down quite a bit by then.
You can probably appreciate how a lot of the builders will leave the pt leads full length until the circuit works... Then shorten/route them later. If at all possible, use anything but green for the 125v primary you replaced... I know it will work but it is very misleading.
+ 1 jjman ... get those rectifier filament wires (yellow ones) taped off and out of the way.
+ 1 Cliff ... I have used a 10vac wall-wart connected to the pt primaries... The 10v makes it easier to do calculations. Should I not use this method?... Or protect it better?
Tony
You can probably appreciate how a lot of the builders will leave the pt leads full length until the circuit works... Then shorten/route them later. If at all possible, use anything but green for the 125v primary you replaced... I know it will work but it is very misleading.
+ 1 jjman ... get those rectifier filament wires (yellow ones) taped off and out of the way.
+ 1 Cliff ... I have used a 10vac wall-wart connected to the pt primaries... The 10v makes it easier to do calculations. Should I not use this method?... Or protect it better?
Tony