If you have a choke with two windings then you must wire them in correct phase (series, parallel or common mode).
I appreciate that most chokes only have a single winding...
The more I look at this thread,
the more ridiculous it seems..
..everyone is trying to help however there is no structured fault location.
I assume you haven't found your fault?
1..why haven't you posted pictures of the top of the amp..we are looking at layout etc.
2..with only the power transformer powered nothing else..
no heaters or B+ you can even unplug the tubes.
Do you get hum then?
If you do its magnetic pick up. The power transformer is exciting the output transformers.
If you have no hum we can take it from there..
Regards
M. Gregg
the more ridiculous it seems..
..everyone is trying to help however there is no structured fault location.I assume you haven't found your fault?
1..why haven't you posted pictures of the top of the amp..we are looking at layout etc.
2..with only the power transformer powered nothing else..
no heaters or B+ you can even unplug the tubes.
Do you get hum then?
If you do its magnetic pick up. The power transformer is exciting the output transformers.
If you have no hum we can take it from there..
Regards
M. Gregg
Hi Gregg
1. I think I have asked twice already for pictures of the top....
2. We figured out a few threads back that it hums without B+ or even heater volts so its pretty obvious.
3. He has moved the OPT's and the hum is reduced.
Look at what I have posted - not all of it was followed up on..
1. I think I have asked twice already for pictures of the top....
2. We figured out a few threads back that it hums without B+ or even heater volts so its pretty obvious.
3. He has moved the OPT's and the hum is reduced.
Look at what I have posted - not all of it was followed up on..
If we could see the top,
it might be possible to make suggestions..
it might be the chassis type causing the problem!
Can the OP see the orientation of the iron circuit or are the TX's in cans?
Are the cans Earthed? Ect..
Is there enough room to put a Earthed steel shield between the Power Tx and the OP Tx's
..so where are the Pics of the top..
Regards
M. Gregg
it might be possible to make suggestions..
it might be the chassis type causing the problem!
Can the OP see the orientation of the iron circuit or are the TX's in cans?
Are the cans Earthed? Ect..
Is there enough room to put a Earthed steel shield between the Power Tx and the OP Tx's
..so where are the Pics of the top..
Regards
M. Gregg
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UPDATE!!!!!
With no B+, hum goes away, with B+ plugged in, even without the input tube, there is a very audible hum.
I am currently using pretty odd resistors for my cathode bias on my 2A3, they are something like 15W Metal Film I think. I might try to change those out to see if it helps at all.
I'm using a 21st Century Maida Regulator as seen here
In response to prior suggestions:
Moving the transformers helped kill the hum with no B+ connected (transformer still plugged in) and a rewiring of my ground did not help. I also cut excess leads and shortened all my paths but it did not help.
OPT's are connected directly to cans, no earth reference on the cans side.
I can try to post pictures of the top, but it will be hard because there is no base constructed yet, I am solely building on the top plate, then I will build a base (like the bottlehead crack) when I fix the electrical stuff. Once I case it up I will surely put an earthed shield around the transformers.
Thanks for all of your help so far! I really appreciate it!
With no B+, hum goes away, with B+ plugged in, even without the input tube, there is a very audible hum.
I am currently using pretty odd resistors for my cathode bias on my 2A3, they are something like 15W Metal Film I think. I might try to change those out to see if it helps at all.
I'm using a 21st Century Maida Regulator as seen here
In response to prior suggestions:
Moving the transformers helped kill the hum with no B+ connected (transformer still plugged in) and a rewiring of my ground did not help. I also cut excess leads and shortened all my paths but it did not help.
OPT's are connected directly to cans, no earth reference on the cans side.
I can try to post pictures of the top, but it will be hard because there is no base constructed yet, I am solely building on the top plate, then I will build a base (like the bottlehead crack) when I fix the electrical stuff. Once I case it up I will surely put an earthed shield around the transformers.
Thanks for all of your help so far! I really appreciate it!
Hi
I had a hum I couldn't find with my first 2A3
Looked everywhere for ground loops (helped me understand it too!) , did the floating, mid point filaments, etc... but really could not solve the hum
It turned out it was the power transformer creating the hum by magnetic field through the output transformers !
Convinced me of separate PSU and Amp blocks typology.
I had a hum I couldn't find with my first 2A3
Looked everywhere for ground loops (helped me understand it too!) , did the floating, mid point filaments, etc... but really could not solve the hum
It turned out it was the power transformer creating the hum by magnetic field through the output transformers !
Convinced me of separate PSU and Amp blocks typology.
Ok, so just to be clear - with NO tubes (no input or output) but B+ you get hum? Yes or No?
Is the regulator attached when you turn it on? Yes or No?
Lastly, do you feel your mains transformer vibrating when you turn on power?
We still would like a pic of the top...
With no INPUT tube, the hum is still there. With no OUTPUT tubes, the hum goes away.
Maybe it is excess magnetic field caused by the additional .1A current draw of the output tubes?
The regulator is always attached when B+ is on, same with the filament regulators for the OT's.
I don't feel the transformer vibrating, but there is an audible mechanical hum coming from it when I connect the B+ to the tubes
Maybe it is excess magnetic field caused by the additional .1A current draw of the output tubes?
The regulator is always attached when B+ is on, same with the filament regulators for the OT's.
I don't feel the transformer vibrating, but there is an audible mechanical hum coming from it when I connect the B+ to the tubes
True... I can't imagine that the reg is the source of the hum... but it is easy to rule out by simply replacing it with a resistor.
Could be that something is drawing to much current out of the HT winding of the PT causing it to hum. Do you have a fuse in the HT?
Did you measure all voltages, including the secondaries of the PT? I remember my first amp: it worked well for some time although the HT was higher than expected. Then I found out that the PT was mislabeled: the bias tap and the center tap were reversed. So instead of (something like) 300-0-50-300 it actually was 300-50-0-300 with the '50'going to ground. My poor EZ81 rectifier was receiving 250V on one side and 350V on the other.
Did you measure all voltages, including the secondaries of the PT? I remember my first amp: it worked well for some time although the HT was higher than expected. Then I found out that the PT was mislabeled: the bias tap and the center tap were reversed. So instead of (something like) 300-0-50-300 it actually was 300-50-0-300 with the '50'going to ground. My poor EZ81 rectifier was receiving 250V on one side and 350V on the other.
Hi Dutch
This might sound crazy, but I actually don't believe in shielding anything that is at line level or higher. I just never found it necessary.
Please do try to give more details about the transformers and post pictures. A picture is worth 1000 words. Most here have "been there, done that" so don't feel embarrassed.
This might sound crazy, but I actually don't believe in shielding anything that is at line level or higher. I just never found it necessary.
Please do try to give more details about the transformers and post pictures. A picture is worth 1000 words. Most here have "been there, done that" so don't feel embarrassed.
There have been some recent discussions about this same problem here. I don't think it is necessary to retype everything, so i'll summarize...
HERE IS THE THREAD
The hum is present with ONLY the output tube connected. So if I remove my input tube, including the AC heater, the hum is still present.
The hum turns in to a more defined hum on lower impedence headphones, and more white-noise on higher impedence headphones.
Moving my earth ground to different points did not solve the problem.
Adding a large filter cap after the regulator for the filament, and doing the same for the HT regulator did not have any effect on the hum.
My umbilical cable has a 1.6mV drop of potential on the ground wire since it is a 5ft cable carrying 100mA through ground.
Grounding one side of the DC filament kills the hum
HERE IS THE THREAD
The hum is present with ONLY the output tube connected. So if I remove my input tube, including the AC heater, the hum is still present.
The hum turns in to a more defined hum on lower impedence headphones, and more white-noise on higher impedence headphones.
Moving my earth ground to different points did not solve the problem.
Adding a large filter cap after the regulator for the filament, and doing the same for the HT regulator did not have any effect on the hum.
My umbilical cable has a 1.6mV drop of potential on the ground wire since it is a 5ft cable carrying 100mA through ground.
Grounding one side of the DC filament kills the hum
In your #1 post, the 2A3 has R//C (1k//200u) cathode complex. If you try grounding either heater leg's (cathode) of 2A3 (DC filament) the negative bias will be "0" V, the 2A3 anode current will be enormous (see datasheet at 0V Vgk)!
1.) Try center trapped filament transformer (AC filament), and connect cathode complex (R//C) to the CT.
2.) If you use hum balance potentiometer (100R), connect cathode complex to center of potentiometer.
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When I tried AC filament, I got enormous hum. I will try again later but not sure if I have a 2.5V CT to test on.
I think its easiest to use DC to reduce hum, isn't it?
This schematic shows, your HT (B+) filtering is very poor. If you use 200uF ONLY, the hum about 6-8V before Maida regulator!
Try using larger first cap, AND CLC or CRC filtering!
Try PSUD power supply simulator, BEFORE you do anything.
PSUD2
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