In that case use your current power transformer and switch to a 5ar4 rectifier you will get close to 390VDC on the B+ for your power tubes. At this voltage it will sound same as having a 400VDC on the B+.
With the money you saved, buy some more KT88 tubes.
HTH.
I have seen this PSU circuit on a lot of Japanese designed PSU.
I have tried it once and it seems to improve the sound (just cannot accept the use of SS on my PSU).
If you do this, make sure to install the bleeder resistor on the RC section going to the driver tube. Sparking digital meter probe on charged capacitor is not good. 😱
Guys, I feel odd, as it looks like I am the only one having troubles with this build, but, as it is my first one maybe I am hunting ghosts.
I have hum in the speakers, on 4 ohm, between 1.7 and 5 mV, this depending on the tube , the configuration (triode, ultra-linear, etc).
What bothers me if that this values are kind of random, in a good day it is very quiet, sometime is not.
Sometimes what if I switch the amplifier on, and I am close to the chassis it starts to have very loud hum. I switch it off and on and then it's fine.
Sometimes while is playing good, it makes hum for 10 seconds and then it stops.
Not sure what's going on. I am really thinking of disassembling it completly.
What values of hum do you have in your speakers ? I measured with a simple volt meter in AC mode.
By the way all the others parameters are ok, voltages are 409 V on B+ and on the drivers I have 194V and 187. Not sure why I have this difference, components should have 1% tolerance. I measured in AC also the ripple on the B+ and it's around 80 mV. I tried to increase the capacitance of the PSU, the HT ripple goes down, but with little measurable effect on the hum on the speakers.
The psu is now configured with CLC-tap-LCRC-tap with the following values
22uF - 10H (81ohm) - 47uF - tap 135 mA - 5H - 47 uF - 100 ohm - 10uF - tap 8 mA
in my experiments I increased the second cap, just after the 10H
I have also DC for heaters.
Best Regards,
Davide
I have hum in the speakers, on 4 ohm, between 1.7 and 5 mV, this depending on the tube , the configuration (triode, ultra-linear, etc).
What bothers me if that this values are kind of random, in a good day it is very quiet, sometime is not.
Sometimes what if I switch the amplifier on, and I am close to the chassis it starts to have very loud hum. I switch it off and on and then it's fine.
Sometimes while is playing good, it makes hum for 10 seconds and then it stops.
Not sure what's going on. I am really thinking of disassembling it completly.
What values of hum do you have in your speakers ? I measured with a simple volt meter in AC mode.
By the way all the others parameters are ok, voltages are 409 V on B+ and on the drivers I have 194V and 187. Not sure why I have this difference, components should have 1% tolerance. I measured in AC also the ripple on the B+ and it's around 80 mV. I tried to increase the capacitance of the PSU, the HT ripple goes down, but with little measurable effect on the hum on the speakers.
The psu is now configured with CLC-tap-LCRC-tap with the following values
22uF - 10H (81ohm) - 47uF - tap 135 mA - 5H - 47 uF - 100 ohm - 10uF - tap 8 mA
in my experiments I increased the second cap, just after the 10H
I have also DC for heaters.
Best Regards,
Davide
Finally done up my amp based on Porkchop's version with LED biased mod on the driver.
Upon powering up, with the volume at minimum, the hums were obvious 🙁
Decided to go ahead with the listening despite the humming. I was shocked! The male vocal from the cd that i was playing really sounded so real and it really gave my goose bumps while listening. Even though the hums is in the background, the amp is still very nice and enjoyable with the volume turn up.
I would appreciate if anyone can give me some idea on the approach on solving the hums? The level of the hums is pretty consistent throughout when i turn the volume knob from min to max. If this kind of hums related to the heater supply coupled to the signal path or it is due to insufficient filtering on the B+?
Thanks in advance!
Upon powering up, with the volume at minimum, the hums were obvious 🙁
Decided to go ahead with the listening despite the humming. I was shocked! The male vocal from the cd that i was playing really sounded so real and it really gave my goose bumps while listening. Even though the hums is in the background, the amp is still very nice and enjoyable with the volume turn up.
I would appreciate if anyone can give me some idea on the approach on solving the hums? The level of the hums is pretty consistent throughout when i turn the volume knob from min to max. If this kind of hums related to the heater supply coupled to the signal path or it is due to insufficient filtering on the B+?
Thanks in advance!
Attachments
Mine have no hum! You're welcome to drop by at my place for a view of my wirings. Call me at 6475 8577.
Cheers!
Zekk
Hi Zekk,
Appreciate your kindness. Let me try to tweak mine b4 I disturb u 🙂
Thanks again
Hi KCMO_One,
Thanks for your input.
You are right about the heater wires. Currently, they are "floating" as I thought this might give some space between the AC and signal lines. I will try out your method. I will use this project (my first tube amp) to practice good wiring (like yours) technique.
Thanks!
i also notice the PTX and choke are position diferent as i have heard to position them 90 degree from your OPTX.
A couple of thoughts:
1) did you used electrolytics for the PSU, give strong consideration to using film and/or ASC oil types.
2) Make sure there are no ground loops accidentally created.
3) consider shielding the signal wires with some tinned copper braid and ground the shield to erath mains.
4) All filament heater wires and power wires should cross signal wires at right angles.
5) I second the need to have filament heaters twisted tightly and run on the chassis.
6) assure you don't have any filament heater wires running parallel to the signal path, especially from the pot to the grid of the 6N1P.
7) Make sure the body of the pot is well grounded to chassis
8) make sure you didn't accidentally leave something that is supposed to be grounded un-grounded (signal ground, OPT common to ground, etc...)
Careful attention to all of your wiring and checking it twice will likely show and ungrounded circuit or a ground loop if the hum is really bad. Take heart, you built a great amp, you will find the proble and get it fixed with some time.
Cheers!
Jeff
1) did you used electrolytics for the PSU, give strong consideration to using film and/or ASC oil types.
2) Make sure there are no ground loops accidentally created.
3) consider shielding the signal wires with some tinned copper braid and ground the shield to erath mains.
4) All filament heater wires and power wires should cross signal wires at right angles.
5) I second the need to have filament heaters twisted tightly and run on the chassis.
6) assure you don't have any filament heater wires running parallel to the signal path, especially from the pot to the grid of the 6N1P.
7) Make sure the body of the pot is well grounded to chassis
8) make sure you didn't accidentally leave something that is supposed to be grounded un-grounded (signal ground, OPT common to ground, etc...)
Careful attention to all of your wiring and checking it twice will likely show and ungrounded circuit or a ground loop if the hum is really bad. Take heart, you built a great amp, you will find the proble and get it fixed with some time.
Cheers!
Jeff
Make sure the body of the pot is well grounded, this can do what you are talking about.
Jeff
Another area I found when I overlooked it I had bad hum problems...this was failing to bring the OPT common to the power supply ground....
I also wondered about the OT secondary common. I currently do not have them referenced to ground, just to the speaker binding posts. I was going to try and add a wire to connect the ground of the OT to the chassis, but since my amp is absolutely quiet, I left it alone.
I will second the tightly twisted heater wiring run close to the chassis and away from signal wiring. I've always done this and had never had a hum problem due to AC coupling.
Also good point about the power supply caps. I've heard that electrolytics used in place of the oil ASC caps are more prone to noise. A quiet power supply is a must is any SE amp.
I was also curious what the IC circuits are in the upper left corner? Maybe some noise is being generated from the solid state stuff?
Glenn
I'm currently enjoying this amp with my Altec speakers, very nice!
I will second the tightly twisted heater wiring run close to the chassis and away from signal wiring. I've always done this and had never had a hum problem due to AC coupling.
Also good point about the power supply caps. I've heard that electrolytics used in place of the oil ASC caps are more prone to noise. A quiet power supply is a must is any SE amp.
I was also curious what the IC circuits are in the upper left corner? Maybe some noise is being generated from the solid state stuff?
Glenn
I'm currently enjoying this amp with my Altec speakers, very nice!
An externally hosted image should be here but it was not working when we last tested it.
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Yeah, the OPT common to ground was part of a schematic I built once that I failed to do. The thing hummed like crazy and motorboated too. I am not certain it is required in all designs and many don't show it on the schematic but, I have since then assumed this needs to happen and have never had that kind of problem since. I have grounded mine in this amp and it works perfectly...not to say that in doing this is why it works so well.
I have noticed too, since I build all of my chassis from wood, that not properly grounding the body of the volume pot will cause a wierd kind of hum that changes pitch and volume when you apprach the amp and volume knob. Not sure why exactly but this is another thing I have learned by experience.
My very first point to point amp was built without consulting this forum or Morgan Jones' book "Builng Valve Amplifiers" and it was a disaster as far as noise went. I highly recommend this book for anybody who is planning to make this a long term hobby. It is loaded with all sorts of valuable info that will keep you out of a hitch. I wish I would have picked it up sooner.
Jeff
I have noticed too, since I build all of my chassis from wood, that not properly grounding the body of the volume pot will cause a wierd kind of hum that changes pitch and volume when you apprach the amp and volume knob. Not sure why exactly but this is another thing I have learned by experience.
My very first point to point amp was built without consulting this forum or Morgan Jones' book "Builng Valve Amplifiers" and it was a disaster as far as noise went. I highly recommend this book for anybody who is planning to make this a long term hobby. It is loaded with all sorts of valuable info that will keep you out of a hitch. I wish I would have picked it up sooner.
Jeff
Errr, I have no idea on how to place the optx and ptx in 90 deg orientation as the optx are potted ones. May I know whether there is any issue on the current placement of all the trans on this amp?
Thanks!
1. I only used MKP caps on the B+ (100uf + 68uf + 0.1uf)
2 to 6. I will review on the ground wiring and redo the filament wiring again.
7. The body of the pot is grounded to the chassis ---> earth
8. Currently the common of the optx is left floating. The 8 ohm and common tap of the optx are connected directly to the binding posts. I will try to common it to the signal ground
Thanks!
Currently, the way I wired the optx secondary is exactly like yours. Only the body of the optx is grounded to the chassis.
The only e-caps used in this amp is only on the cathode of the power tubes (2x 100uf,100v Sprague atom each)
The board on at the corner is for some fancy stuff as describe below.
1. Power up the tubes in this sequence. 6.3V first to driver and power tubes and then delay the 5V to tube rectifier by ~10sec (adjustable)
2. Monitor the B+ voltage to ensure it is ~ 98% of the intended value (400v)
I have bypassed it but still doesn't help in the humming.
I will post the schematics diagram of my amp soon.
Thanks!
Power Supply Choke
I know it is recommended to orient the output xfmrs and power supply xfmr 90 degrees in relation to each other. Is it also recommended to position the power supply choke 90 degrees in reference to the power transformer? Then it would be in-line with the OPTs. Since the PS xfmr and PS choke are related to the same circuit should I leave them both aligned the same so they are then rotated 90 degrees in relation to the OPTs?
I know it is recommended to orient the output xfmrs and power supply xfmr 90 degrees in relation to each other. Is it also recommended to position the power supply choke 90 degrees in reference to the power transformer? Then it would be in-line with the OPTs. Since the PS xfmr and PS choke are related to the same circuit should I leave them both aligned the same so they are then rotated 90 degrees in relation to the OPTs?
Hi,
Is it possible to substitute the 6n1p with a 6922? I just worry if the 6922 may not withstand the high voltages but i've got lots of 6922s. Thanks.
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