Yeah, I braided left right and ground, less to get rid of noise, but just to keep wires from being everywhere. I'll try redoing this.
I moved the red center-tap wires closer to the sides and the hum reduced dramatically. There is still a little on one side, and a lot on the other, but less than there was.
Also, one of the tubes (a tubg-sol) while the most microphonic of the bunch and the one must prone to radiator like clanging, also has the least hum. The chassis is a 16 inch wide sheet of aluminum with a tube in the middle, so chassis dampening/support does seem to be in order.
I moved the red center-tap wires closer to the sides and the hum reduced dramatically. There is still a little on one side, and a lot on the other, but less than there was.
Also, one of the tubes (a tubg-sol) while the most microphonic of the bunch and the one must prone to radiator like clanging, also has the least hum. The chassis is a 16 inch wide sheet of aluminum with a tube in the middle, so chassis dampening/support does seem to be in order.
dsavitsk said:
Had several NOS tubes which did this in well designed circuits, typ pentodes and multi electrode are more susp than triodes. There is only one recourse.....buy from a reputable supplier; at same time request a tap test to weed out tubes with bad microphony. Most decent vendors will exchange extreme cases.
One cannot rule out a tube gone into self oscillation from bad layout or internal screen not grounded will show sim symptoms i.e become very touch sensitive and audio may be demodulated by next tube. An oscilloscope will show up.
richj
with all due respect, the wiring is a bit not so ideal with wires cris-crossing one another. if you wanted to have a good look on the inside (the outside is fantastic by the way), then you can try a bus ground with localized star.
however, i would normally have minimized hookup wires and would echo EC8010's suggestion. I use star on all my projects except the gordon rankin 807 which i used bus.
still it wouldn't solve microphonic tubes and you have some.
if you have a scope you can probe your circuit for noise. although myself did not enjoy a scope until recently, when most of my projects were done.
however, i would normally have minimized hookup wires and would echo EC8010's suggestion. I use star on all my projects except the gordon rankin 807 which i used bus.
still it wouldn't solve microphonic tubes and you have some.
if you have a scope you can probe your circuit for noise. although myself did not enjoy a scope until recently, when most of my projects were done.
Re: Throw Throw Throw Throw Throw Away.....nt
It does look like 3 of the 4 tubes I have are unusable and will be pitched. The 4th is very microphonic, but is kind of noise free, and can at least be used for a few days until I get a new one. Once it warms up (after about an hour) it stops clanging and banging for the most part.
Can anyone recommend a reliable source for getting a 6080 that is tested for low noise/microphonics and is returnable?
I don't think any respect is due at all. I'm new to this and no doubt have tons to learn
Thanks. It is not really that nice, but I used padauk for the wood which is really pretty.
I did try to keep things from criss crossing, and tried to star the ground, but it got away from me a bit. Taking Sy's suggestion, at least what I think was his suggestion, and moving the two ground return wires to the outside helped quite a bit. There is still a little bit of hum, but onlya little bit. I am going to go back in and try to clean it even more.
I also added damoig material to the bottom of the aluminum, and that helped reduce some microphonics.
Even with all that, the thing actually sounds quite good.
It does look like 3 of the 4 tubes I have are unusable and will be pitched. The 4th is very microphonic, but is kind of noise free, and can at least be used for a few days until I get a new one. Once it warms up (after about an hour) it stops clanging and banging for the most part.
Can anyone recommend a reliable source for getting a 6080 that is tested for low noise/microphonics and is returnable?
arnoldc said:
I don't think any respect is due at all. I'm new to this and no doubt have tons to learn
arnoldc said:
Thanks. It is not really that nice, but I used padauk for the wood which is really pretty.
I did try to keep things from criss crossing, and tried to star the ground, but it got away from me a bit. Taking Sy's suggestion, at least what I think was his suggestion, and moving the two ground return wires to the outside helped quite a bit. There is still a little bit of hum, but onlya little bit. I am going to go back in and try to clean it even more.
I also added damoig material to the bottom of the aluminum, and that helped reduce some microphonics.
Even with all that, the thing actually sounds quite good.
I doubt if any vendor will allow you to reject 6080 for microphony. The thing is, after all, a dirty great brute intended to be the series pass element in a power supply.
However, it occurs to me that that may not be the problem. It may be that you have RF oscillation - that can cause microphony and noise. Have you got 1k carbon grid-stopper resistors on the grid pins before any other connections? Also, a 100nF between the top of the programming resistor on the anode CCS and the bottom of the cathode circuit would help.
However, it occurs to me that that may not be the problem. It may be that you have RF oscillation - that can cause microphony and noise. Have you got 1k carbon grid-stopper resistors on the grid pins before any other connections? Also, a 100nF between the top of the programming resistor on the anode CCS and the bottom of the cathode circuit would help.
The series pass valve in a regulator operates as a cathode follower, so it doesn't amplify its noise. Further, it has a negative feedback loop wrapped around it that will reduce any noise it generates. Conversely, a gain stage amplifies its noise and might not have a feedback loop around it. Thus, a valve designed for series pass use will not be designed or manufactured with noise as a primary consideration, whereas a valve designed to be used as an amplifier must pay attention to noise. If we use a device in an application for which it was not designed, we should expect problems and we can hardly turn round to the manufacturer/distributor and say, "I'm using your product in a circuit for which it wasn't designed, but it's your problem."
Hi,
Hum is always a problem with the 6as7/6080. All the schematics i've seen used a lot uf's. Your power supply looks good but maybe needs more capacitance. Look at this schematic:
http://www.audiokit.it/ITAENG/KitElettr/MEGA/InterfMhz/interfsch.jpg
I have also found that some 6as7's in certain circuits make strange noises, like the ones you described.
Hum is always a problem with the 6as7/6080. All the schematics i've seen used a lot uf's. Your power supply looks good but maybe needs more capacitance. Look at this schematic:
http://www.audiokit.it/ITAENG/KitElettr/MEGA/InterfMhz/interfsch.jpg
I have also found that some 6as7's in certain circuits make strange noises, like the ones you described.
Hi EC8010,
I think your point is moot, since in a grounded cathode stage a 6AS7 has a gain of 2 (at most) - it doesn´t amplify noise much.
So, if it has noticable noise at a gain of less than 2, it also will have noise when operating as CF with a gain of less than 1. Maybe 1/2, maybe a 1/4, but ...
Tom
EC8010 said:
I think your point is moot, since in a grounded cathode stage a 6AS7 has a gain of 2 (at most) - it doesn´t amplify noise much.
So, if it has noticable noise at a gain of less than 2, it also will have noise when operating as CF with a gain of less than 1. Maybe 1/2, maybe a 1/4, but ...
Tom
EC8010 said:
There are 1K Riken resistors right on the pins. I don't know the difference in sound between microphonics and and RF oscillation, but I do know that if you talk into the tube it comes out the speakers.
For the 100nF, I'm not sure I understand where it would be placed. By top of the programming resistor, does this mean right where B+ first connects to the CCS? And for bottom of the cathode circuit, is that just ground?
stalker said:
Hmmm. According to the duncan amps program, ripple before the CCS is just a few micro-volts. The CCS should reduce it even more. I do have a couple of 56uF Solens I could cram in there, however. Also, would it be worth changing the heater to DC? It doesn't really sound like AC hum, but maybe that's what is inducing the tube noise?
Pete's original schematic (http://www.pmillett.com/images/lowmu_sch.PDF) used a 7236 (though he does suggest the 6as7 as ao option.) I think I can use it by changing just a couple of resistors, so I might give it a shot too.
-d
Tubes4e4 said:
I have called attention for the fact (post# 16 ) , that probably the noise came from the CCS...but nobody care...
dsavitsk..what is the voltage between the anode of the tube and the + rail?...I suspect that the transistors are in saturation state , therefore having a very low impedance between the tube anode and power rail..
Some updates:
I increased the bias on the led's to 4mA (Doc at Bottlehead actually suggests biasing to 10% of the current over 10mA whilePJ says 20% I may increase closer to 8mA at some point to see what happens.) I also put a 1uF film cap across each one of the led's. I tried some of the noisy tubes, and they were still noisy. They may have been a little less noisy, but not hugely.
However, I happen to be fortunate to live down the street from Triode Electronics (down the street is relative here. Chicago is a big place.) I called them, and even though their website says they are closed on Saturday and they don't list the 6080 as a tube they carry, they told me they had some and I could come in to get them. They sold me a couple of Philips JAN 6080WC's. I've only tried one of them so far. At first there was a high pitched squeel -- less like oscillation, and more like ringing due to vibration. This went away after about 20 minutes. Other than that, almost all of the noise is gone. The tube does not seem to sound quite as good as the Tung-Sol. The Tung-Sol had a huge open sound (though part of that may be microphonic reverb) while this one is a little dead and muffled sounding. It is getting better -- or I am getting used to it -- with use.
So, thanks to everyone who has helped here. I think there is more to be done, but at least for now things are working reasonably well.
-d
I increased the bias on the led's to 4mA (Doc at Bottlehead actually suggests biasing to 10% of the current over 10mA whilePJ says 20% I may increase closer to 8mA at some point to see what happens.) I also put a 1uF film cap across each one of the led's. I tried some of the noisy tubes, and they were still noisy. They may have been a little less noisy, but not hugely.
However, I happen to be fortunate to live down the street from Triode Electronics (down the street is relative here. Chicago is a big place.) I called them, and even though their website says they are closed on Saturday and they don't list the 6080 as a tube they carry, they told me they had some and I could come in to get them. They sold me a couple of Philips JAN 6080WC's. I've only tried one of them so far. At first there was a high pitched squeel -- less like oscillation, and more like ringing due to vibration. This went away after about 20 minutes. Other than that, almost all of the noise is gone. The tube does not seem to sound quite as good as the Tung-Sol. The Tung-Sol had a huge open sound (though part of that may be microphonic reverb) while this one is a little dead and muffled sounding. It is getting better -- or I am getting used to it -- with use.
So, thanks to everyone who has helped here. I think there is more to be done, but at least for now things are working reasonably well.
-d
I seem to have been premature here in declaring everything okay ...
Most of the major noise is gone, however, I am now getting a high pitched squeel that comes and goes. It could just be that it is this tube's special noise, but I doubt that.
There are 1uF film caps across each LED in the CCS as in the schematic above. I also added 0.1uF VitQ caps to bypass the cathode bypass caps -- this improved the sound remarkably. I did measure the caps before installing them, but I am open to the possibiliy that one of them is leaky and that they are the culprite -- I don't remember the squeel before putting them in. It does not change as the volume changes.
However, I also think that I should pull out a lot of the wiring and rethink the grounding. Any thoughts on things to look at before doing this, whether a leaky cap is a possibility, and ways to improve the grounding scheme?
-d
Most of the major noise is gone, however, I am now getting a high pitched squeel that comes and goes. It could just be that it is this tube's special noise, but I doubt that.
There are 1uF film caps across each LED in the CCS as in the schematic above. I also added 0.1uF VitQ caps to bypass the cathode bypass caps -- this improved the sound remarkably. I did measure the caps before installing them, but I am open to the possibiliy that one of them is leaky and that they are the culprite -- I don't remember the squeel before putting them in. It does not change as the volume changes.
However, I also think that I should pull out a lot of the wiring and rethink the grounding. Any thoughts on things to look at before doing this, whether a leaky cap is a possibility, and ways to improve the grounding scheme?
-d
Bypassing an LED with 1uF won't do much. An ideal (for this purpose) red LED has a slope resistance of about 5R, and even a less than ideal red LED is likely to be less than 20R. 1uF will only begin to affect 20R at 8kHz, and would only affect the best red LED at 32kHz.
I think you're right, it's the grounding (isn't it always?) that's likely to be the problem. Star ground the whole thing to one point. Even if it doesn't cure the problem, it's the right way to go.
I think you're right, it's the grounding (isn't it always?) that's likely to be the problem. Star ground the whole thing to one point. Even if it doesn't cure the problem, it's the right way to go.
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