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-   -   noisy noisy noisy noisy noisy tube (https://www.diyaudio.com/forums/tubes-valves/73755-noisy-noisy-noisy-noisy-noisy-tube.html)

dsavitsk 10th February 2006 06:47 PM

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.

richwalters 10th February 2006 08:41 PM

Quote:

Originally posted by dsavitsk


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.


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

amperex 10th February 2006 10:36 PM

Throw Throw Throw Throw Throw Away.....nt
 
.

arnoldc 11th February 2006 03:25 AM

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.

dsavitsk 11th February 2006 06:20 AM

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?

Quote:

Originally posted by arnoldc
with all due respect, the wiring is a bit not so ideal with wires cris-crossing one another.
I don't think any respect is due at all. I'm new to this and no doubt have tons to learn :)

Quote:

Originally posted by arnoldc
(the outside is fantastic by the way)
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.

EC8010 11th February 2006 09:26 AM

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.

Tubes4e4 11th February 2006 10:41 AM

Hi EC8010,

Quote:

Originally posted by EC8010
[B]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.
So it is okay to you that a pass tube in PSU service is noisy? :bigeyes:

Nah, we donīt want regulators (regulated voltages) to be noisy, do we?

Tom

EC8010 11th February 2006 11:04 AM

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."

Cassiel 11th February 2006 11:28 AM

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/KitEle.../interfsch.jpg

I have also found that some 6as7's in certain circuits make strange noises, like the ones you described.

Tubes4e4 11th February 2006 02:00 PM

Hi EC8010,

Quote:

Originally posted by EC8010
The series pass valve in a regulator operates as a cathode follower, so it doesn't amplify its noise.
I think your point is moot, since in a grounded cathode stage a 6AS7 has a gain of 2 (at most) - it doesnīt 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


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