I discovered today that one of my (new) 6SN7’s from my stock is quite noisy. I changed the tube and it was a huge improvement (> 20 dB).
I read about reconditioning a tube by heating the tube for 24 hours (or more) and of course I can try this.
What are your thoughts on this and what’s your experience?
Regards, Gerrit
I read about reconditioning a tube by heating the tube for 24 hours (or more) and of course I can try this.
What are your thoughts on this and what’s your experience?
Regards, Gerrit
I got a set of 4 - UK6SN7, one of them is noisy in the amp but work fine in Preamp. Have never thought of heating the tube. Same issue after 100 hours, probably the tube itself.
Hi all,
I know it’s the tube and not the circuit. This particular tube is a JJ tube.
I have the heater elevated to approx. 40 volts DC to get lowest hum.
Buying new tubes is an option, but I am curious what others have done.
Regards, Gerrit
I know it’s the tube and not the circuit. This particular tube is a JJ tube.
I have the heater elevated to approx. 40 volts DC to get lowest hum.
Buying new tubes is an option, but I am curious what others have done.
Regards, Gerrit
I like Tung-Sol 6SN7GTB, got 8 of them without problem. And 4 of Shuguang Treasure CV181-Z. These was on eBay from US reliable tubes sellers.
I only afraid of UK-6SN7 that makes from china that I don't think I would buy again but it sounds great. Don't have other brands so I don't know. Got these from Aliexpres.
I only afraid of UK-6SN7 that makes from china that I don't think I would buy again but it sounds great. Don't have other brands so I don't know. Got these from Aliexpres.
If the noise is excess noise due to an interface layer in the cathode, by running it on a highish heater voltage and substantial anode current for some time. I never tried that, though, and a brand new valve should not have such an interface layer anyway.
Do you have 1k grid stoppers for each grid; connected right at the socket tap?
Sometimes, with a particular circuit, particular wiring, and particular wiring dress, some tubes will operate.
Given the capacitances, u, Gm, and rp of the 6SN7, it is fully capable of sustaining oscillation at RF frequencies.
Steady, bursted, or spread noise.
Try the grid stoppers, if that fixes it, then probably any 6SN7 will work in that socket, with that circuit, wiring, and wire dress.
And, separate from the oscillation problem, some 6SN7 are more linear than others, so you just might prefer the "sound" of tube that was oscillating when there were no grid stoppers.
Design an amplifier, get an oscillator.
Design an oscillator, get an amplifier.
It has happened multiple times.
Parasitic L and parasitic C will always be with us.
Sometimes, with a particular circuit, particular wiring, and particular wiring dress, some tubes will operate.
Given the capacitances, u, Gm, and rp of the 6SN7, it is fully capable of sustaining oscillation at RF frequencies.
Steady, bursted, or spread noise.
Try the grid stoppers, if that fixes it, then probably any 6SN7 will work in that socket, with that circuit, wiring, and wire dress.
And, separate from the oscillation problem, some 6SN7 are more linear than others, so you just might prefer the "sound" of tube that was oscillating when there were no grid stoppers.
Design an amplifier, get an oscillator.
Design an oscillator, get an amplifier.
It has happened multiple times.
Parasitic L and parasitic C will always be with us.
Yep, grid stoppers are there. It’s not an oscillation, it’s definitely the tube. I use a noise probe and an oscilloscope/spectrumanalyzer as well.
I still have my HAM license, so I know about RF.
Regards, Gerrit
I still have my HAM license, so I know about RF.
Regards, Gerrit
gerrittube,
We know RF.
I once measured sub-mm 500 GHz in waveguide. Over the decades, some of us called that Fantasy Land, not RF.
We did not have a 3,500 GHz signal source, and we did not have a 3,500 GHz mixer, so we could not test the calculated theoretical limits of the Spectrum Analyzer at that frequency.
I did lots of lower frequency waveguide tests too.
I love that some waveguide modes were 200 Ohm impedance; not as low impedance as coax, and not as high impedance as free space.
Now I am satisfied to use vacuum tubes.
We know RF.
I once measured sub-mm 500 GHz in waveguide. Over the decades, some of us called that Fantasy Land, not RF.
We did not have a 3,500 GHz signal source, and we did not have a 3,500 GHz mixer, so we could not test the calculated theoretical limits of the Spectrum Analyzer at that frequency.
I did lots of lower frequency waveguide tests too.
I love that some waveguide modes were 200 Ohm impedance; not as low impedance as coax, and not as high impedance as free space.
Now I am satisfied to use vacuum tubes.
There are plenty of tales of old Russian Melz tubes going noisy and being cured by removing the old pin solder and resoldering. Don’t know if current JJ tubes are worth the effort but something to keep in mind with expensive tubes.