Since 2 days, I have a noise coming out the transformer... I can ear it at 2-3 feet... A year ago, I found the same problem with my DIY ALEPH30, I solve the problem by buying an other thanformer, Before, I was using 1 transformer for the 2 channel, With two transformer, the load is reduce....and I never ear any noise after that!
So now, I changed the heater configuration to drop the charge, and the noise is still there...
Do you think my transformer is bad???
Maybe I ran the low voltage output to hard and now the transformer is broken???
So now, I changed the heater configuration to drop the charge, and the noise is still there...
Do you think my transformer is bad???
Maybe I ran the low voltage output to hard and now the transformer is broken???
Some less expensive transformers have 4 bolts in the corners to hold the core stack together. If yours is one of those, first try and tighten the bolts.
Normally the core will hum if the transformer has been overheated. You should be able to hold your hand on the transformer when the unit is ON at normal room temperature. Most people can hold onto 55 degrees C. If yours is too hot there are three possibilities; 1. It was damaged due to a temporary condition 2. It is always in overload because it is undersized and 3. something is wrong with your circuit.
Before you buy a new transformer verify that nothing will damage the new one. If the current one is too hot either fix the problem or buy a larger VA unit. Those tube heater circuits can draw quite high currents. Get the tube data sheet(s) and add all he filament currents up, then verify against the transformer data sheet.
Normally the core will hum if the transformer has been overheated. You should be able to hold your hand on the transformer when the unit is ON at normal room temperature. Most people can hold onto 55 degrees C. If yours is too hot there are three possibilities; 1. It was damaged due to a temporary condition 2. It is always in overload because it is undersized and 3. something is wrong with your circuit.
Before you buy a new transformer verify that nothing will damage the new one. If the current one is too hot either fix the problem or buy a larger VA unit. Those tube heater circuits can draw quite high currents. Get the tube data sheet(s) and add all he filament currents up, then verify against the transformer data sheet.
My transformer is a ¨Classic plate and filament transformer¨ from Hammond. I notice that, when I press the transformer with my hand, the noise almost gone...
For the bolt, mine have 4 hole in the coner but there no bolt in. There is only two bolt in the middle... tommorow, I will buy some bolt and try that. For the temperature, after 4 hour, the temperature is not very hot....
Thank you again hermanv.
For the bolt, mine have 4 hole in the coner but there no bolt in. There is only two bolt in the middle... tommorow, I will buy some bolt and try that. For the temperature, after 4 hour, the temperature is not very hot....
Thank you again hermanv.
im about half way thru building the PV12 and have some B+ problems. i intended to use the cct below below but things are getting out of hand here as the target B+ is 250V.
from the transfo its 250Vac into a bridge. the bridge output is also 250V (rippled). shouldnt this be 1.414 times the 250Vac?
then the 250Vdc(ripple) goes into the RC cct below and at the output i have like 380Vdc which keeps going up and up. it just keeps going up and i shut it off.
can someone help me out here to get the 250Vdc RC based? thks
from the transfo its 250Vac into a bridge. the bridge output is also 250V (rippled). shouldnt this be 1.414 times the 250Vac?
then the 250Vdc(ripple) goes into the RC cct below and at the output i have like 380Vdc which keeps going up and up. it just keeps going up and i shut it off.
can someone help me out here to get the 250Vdc RC based? thks
Attachments
The 250 V rippled is due to no filter. The capacitor charges to the peak of the ripple value. The peak value of a sine wave is 1.414 times the RMS voltage. Without a capacitor at all, the DC will be equal to the RMS value.
Step 1:
Open the bridge and measure the AC voltage. Your drawing shows 200, the text says 250. 250VAC would equal about 350VDC with no load.
I'm guessing that the 100 Ohm resistors driving the 100uF capacitors are what is causing the slow rise. Is the capacitor voltage high enough to allow the circuit to rise to maximum? Do you own a variac? If so set it to 1/2 voltage wait for the circuit to stabilize and then turn the variac up slowly.
Step 2:
Add a temporary load resistor, if you own a 5 watt 24K Ohm resistor that would be a good value, since that equals 15mA (at 350V). The voltage may well be less under load.
Normally when this kind of unexpected thing happens it's because something you think is true or wired one way isn't what you think it was. Double check things. There's a reason the circuit is behaving as you describe, with some patience we can find it.
Step 1:
Open the bridge and measure the AC voltage. Your drawing shows 200, the text says 250. 250VAC would equal about 350VDC with no load.
I'm guessing that the 100 Ohm resistors driving the 100uF capacitors are what is causing the slow rise. Is the capacitor voltage high enough to allow the circuit to rise to maximum? Do you own a variac? If so set it to 1/2 voltage wait for the circuit to stabilize and then turn the variac up slowly.
Step 2:
Add a temporary load resistor, if you own a 5 watt 24K Ohm resistor that would be a good value, since that equals 15mA (at 350V). The voltage may well be less under load.
Normally when this kind of unexpected thing happens it's because something you think is true or wired one way isn't what you think it was. Double check things. There's a reason the circuit is behaving as you describe, with some patience we can find it.
thks for the input hermanv.
im using the RC section only of the cct. (minus the transfo info)
the transfo im using has 0, 250Vac, 250Vac or 310Vac at 0.15Amp. but actually when measured open, the dvm shows higher than the specified values for all.
the bridge comes after that and then all the RCs as above.
i managed to run into Duncans PS program and it seems that a 1Kohm res in series is missing between the bridge and the first RC. from there the B+ reading seems more realistic.
the program also needs a Rload which i keyed in at 7.7kohm because the 12AU7 has plate resistance at 7.7k......is this the Rload i should use?
thks
im using the RC section only of the cct. (minus the transfo info)
the transfo im using has 0, 250Vac, 250Vac or 310Vac at 0.15Amp. but actually when measured open, the dvm shows higher than the specified values for all.
the bridge comes after that and then all the RCs as above.
i managed to run into Duncans PS program and it seems that a 1Kohm res in series is missing between the bridge and the first RC. from there the B+ reading seems more realistic.
the program also needs a Rload which i keyed in at 7.7kohm because the 12AU7 has plate resistance at 7.7k......is this the Rload i should use?
thks
No. A better way is to load the cct via a CCS (set it instead of an R load) for the total quiescent draw of the cct. That'll give you a good idle similation. Alternatively, if you know the quiescent current and the B+ use R=V/I to get a value of R for the cct.puginfo said:
ok then from the 12AU7 datasheet, Ia is 10.5mA so since there are 2 of them that becomes 20.1mA. then Rload becomes 12kohms at 250Vdc. it that ok for quiescent current?
cheers
cheers
Are there 2 bottles? If so that's 4 triodes.puginfo said:
The datasheet value for Ia may or may not be correct for the CJ cct, but will be close enough to experiment with.
"Are there 2 bottles? If so that's 4 triodes"
20.1mA X 2 = 40.2mA
so its 6219ohms at 250Vdc or something near.
BTW, on the datasheet is Ia, the max anode current or the quiescent current?
the CJ cct seems to have one B+ going thru 82.5kohm and the other B+ going directly into the anode. what would be the effective R then? do we consider the 7.7kohm plate res?
thks
20.1mA X 2 = 40.2mA
so its 6219ohms at 250Vdc or something near.
BTW, on the datasheet is Ia, the max anode current or the quiescent current?
the CJ cct seems to have one B+ going thru 82.5kohm and the other B+ going directly into the anode. what would be the effective R then? do we consider the 7.7kohm plate res?
thks
So that would be 438VDC peak with 150mA load. This explains the higher than expected output you wondered about in your previous post.puginfo said:
No, plate resistance is the lower limit of resistance. By biasing the tubes only partially "on" the current will be less. 7-10mA per tube might be a good guess. It shouldn't be all that important once the supply starts working like it's supposed to. Output voltage will be lowered by the series R's in the filters at about 1V to 1.5V per mA. Since the resulting output is higher than expected, maybe the 1K should be increased to 2K?puginfo said:
If the total load is 30mA the 1K resistor should be at least 2 watts (never run resistors at their full power rating, they get hotter than blazes and it effects their life).
If this were my project, I would add a film capacitor, 1 to 10uF at the last filter stage for effective high frequency bypass.
i would like to thank everyone for this project. just fired up the PV12 with 12AU7s just now and has been sounding good so far.
its all wired up in a wooden base for test run. sounds very good with my musical fidelity amp and philips cdp. some observations below and some help needed:
1 - B+ is now at 250V and may have 252V after 1 hr. after backward simulation on the Duncans PS prog, it seems that the PV12 Rload is at 26.15kohms. i used a 4XRC network and 250Vdc and 26.15k yields 9.6mA only. not sure how this goes with Ia but would the PS able to support the additional current on need? is the 9.6mA quiscent current?
2 - the L7812CV puts out 11.88v much to my surprise. swapped for another and it was the same. i used a 1000u at the in and 1000u at the out...very simple cct. any probs here?
3 - played good and suddenly came on with a sharpish buzz on both channels which goes up and down with amp volume. still present without input music. what would this be? earthing?
cheers
its all wired up in a wooden base for test run. sounds very good with my musical fidelity amp and philips cdp. some observations below and some help needed:
1 - B+ is now at 250V and may have 252V after 1 hr. after backward simulation on the Duncans PS prog, it seems that the PV12 Rload is at 26.15kohms. i used a 4XRC network and 250Vdc and 26.15k yields 9.6mA only. not sure how this goes with Ia but would the PS able to support the additional current on need? is the 9.6mA quiscent current?
2 - the L7812CV puts out 11.88v much to my surprise. swapped for another and it was the same. i used a 1000u at the in and 1000u at the out...very simple cct. any probs here?
3 - played good and suddenly came on with a sharpish buzz on both channels which goes up and down with amp volume. still present without input music. what would this be? earthing?
cheers
Hello puginfo;
Sure sounds like a cathode filament short, either inside a tube or in the wiring.
Based on the previous discussions I'd guess that careful thoroughness is not your strongest suit. Look very carefully for bad solder joints or shorts.
Both channels or only one?
Sure sounds like a cathode filament short, either inside a tube or in the wiring.
Based on the previous discussions I'd guess that careful thoroughness is not your strongest suit. Look very carefully for bad solder joints or shorts.
Both channels or only one?
Hello puginfo;
I meant no insult, did you find the noise source? If it goes up and down with volume pot setting it's the problem is ahead of the pot.
ps. 11.88 volts is exactly 1% less than 12V, this is within meter and/or regulator specifications.
I meant no insult, did you find the noise source? If it goes up and down with volume pot setting it's the problem is ahead of the pot.
ps. 11.88 volts is exactly 1% less than 12V, this is within meter and/or regulator specifications.
the setup which i described earlier was a test setup on the wooden board. so i did not have a place to secure the earth lead from the wall plug. i had to secure that to the transfo body/frame.
the buzz seems to have gone away without this lead attached to the transf. body. there is no volume pot in this one and i use the digital volume from the philips 930. anyway, i had dismantled the whole thing to bulid it back in a proper metal enclosure. now very busy cutting, sawing & filing away this thing which was a telco power rectifier in its previous life.
will post soon. cheers
the buzz seems to have gone away without this lead attached to the transf. body. there is no volume pot in this one and i use the digital volume from the philips 930. anyway, i had dismantled the whole thing to bulid it back in a proper metal enclosure. now very busy cutting, sawing & filing away this thing which was a telco power rectifier in its previous life.
will post soon. cheers
Since a couple of weeks, I can hear sometime an high frequency noise comming out from one of the speakers and sometime, it came out from the preamplifier itself!!!
What can cause that noise?? I tried to change the tube and the noise still there sometime!!
Thank you!
What can cause that noise?? I tried to change the tube and the noise still there sometime!!
Thank you!
I have an other question, maybe Hermanv or anybody else can answer me!
I run my preamp with the original 47.5 Ohm resistor at the input and at the output but if I look the the Harmanv modification circuit to reduce the gain, it has an 425 Ohm resistor at the input and nothing at the output! So, I run my preamp with the modification schematic of Hermanv but with the two original 47.5 Ohm resistor, is that OK ?
I run my preamp with the original 47.5 Ohm resistor at the input and at the output but if I look the the Harmanv modification circuit to reduce the gain, it has an 425 Ohm resistor at the input and nothing at the output! So, I run my preamp with the modification schematic of Hermanv but with the two original 47.5 Ohm resistor, is that OK ?
that 425ohm resistor at the input limits the input signal to stay away from input saturation. it can also be done with a 100k pot which eventually acts a potentio (for say a pre and power block setup). taking output from the cathode cct directly is fine and do not have to have another resistor. the output resistor you mention could be to limit the output voltage so that it will not saturate the section after it (the power block).
the high freq pitch.....check yr earthing first. the should be 2 types - signal gnd and power gnd both collecting star topology and are placed furthest apart. i wire up the signal gnd star to the power gnd star thru a 10kohm resistor.
the high freq pitch.....check yr earthing first. the should be 2 types - signal gnd and power gnd both collecting star topology and are placed furthest apart. i wire up the signal gnd star to the power gnd star thru a 10kohm resistor.
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