Hello
I have a very interesting problem.
Recently I have ordered three Gold Lion ECC83 tubes for my DIY Marantz M7 preamp. I wanted a change in my system so I decided to change old JJ ECC803S’s. I have swapped the tubes and started it up. After the initial warm up of heaters, high voltage kicked in and immediately there was a buzz on my mid-range speaker on only right channel (there was no buzz with JJ tubes).
Tubes played beautifully, but there was that buzz (does not depend on a volume level).
I measured it with oscilloscope which can be found in attachment.
So I decided to swap tubes one by one with JJ tubes to find a problem (JJ tubes are still good). First one was the cathode follower tube (U3 on schematics, in attachment). I swapped the tube and there was no buzz. So I had two Gold lion tubes (preamp section) and one JJ tube (cathode follower) and the buzz was gone. Then I wanted to check if that tube is bad. I swapped JJ tube from cathode follower (U3) with another Gold lion tube from preamp section (U2). JJ tube was now in preamp and Gold lion as cathode follower again. The buzz was back.
So my conclusion is that the problem is in the Gold lion tube as cathode follower and that the tube itself is not bad. It seems that the Gold lion tubes are more sensitive than JJ tubes.
I tried to shield the tube itself with an improvised shield (aluminum foil wrapped around cardboard tube box and connected to GND) but there was no difference.
The high voltage is regulated with linear regulator and the heaters are powered via DC voltage (linear regulator as well). I have posted schematics, pcb layout, oscilloscopes measurements and photo of the preamp inside the housing.
On the preamp_1.jpg photo, red lines are AC line of power supply and green lines are AC lines for VU meter lamps that can be switched on or off (the tube buzzes either in on or off position). All AC lines are quite far away from the U3 tube.
So my questions are:
- what could be the problem?
- why is only the Gold lion tube affected with this and why the JJ tube is not?
- why did I hear u buzz in my mid-range speaker on only one channel (difference between buzz in left and right channel)?
Thank you in advance
I have a very interesting problem.
Recently I have ordered three Gold Lion ECC83 tubes for my DIY Marantz M7 preamp. I wanted a change in my system so I decided to change old JJ ECC803S’s. I have swapped the tubes and started it up. After the initial warm up of heaters, high voltage kicked in and immediately there was a buzz on my mid-range speaker on only right channel (there was no buzz with JJ tubes).
Tubes played beautifully, but there was that buzz (does not depend on a volume level).
I measured it with oscilloscope which can be found in attachment.
So I decided to swap tubes one by one with JJ tubes to find a problem (JJ tubes are still good). First one was the cathode follower tube (U3 on schematics, in attachment). I swapped the tube and there was no buzz. So I had two Gold lion tubes (preamp section) and one JJ tube (cathode follower) and the buzz was gone. Then I wanted to check if that tube is bad. I swapped JJ tube from cathode follower (U3) with another Gold lion tube from preamp section (U2). JJ tube was now in preamp and Gold lion as cathode follower again. The buzz was back.
So my conclusion is that the problem is in the Gold lion tube as cathode follower and that the tube itself is not bad. It seems that the Gold lion tubes are more sensitive than JJ tubes.
I tried to shield the tube itself with an improvised shield (aluminum foil wrapped around cardboard tube box and connected to GND) but there was no difference.
The high voltage is regulated with linear regulator and the heaters are powered via DC voltage (linear regulator as well). I have posted schematics, pcb layout, oscilloscopes measurements and photo of the preamp inside the housing.
On the preamp_1.jpg photo, red lines are AC line of power supply and green lines are AC lines for VU meter lamps that can be switched on or off (the tube buzzes either in on or off position). All AC lines are quite far away from the U3 tube.
So my questions are:
- what could be the problem?
- why is only the Gold lion tube affected with this and why the JJ tube is not?
- why did I hear u buzz in my mid-range speaker on only one channel (difference between buzz in left and right channel)?
Thank you in advance
Attachments
Parasitic oscillations aren't unknown in cathode followers. Your schematic shows cathode stops (the cathode resistors R23 and R25 themselves) but no grid stops. Maybe also important is the lack of local bypassing of the followers' B+. You might try that first.
If the new, hotter?, valves oscillate, that means that the originals are almost oscillating.
All good fortune,
Chris
If the new, hotter?, valves oscillate, that means that the originals are almost oscillating.
All good fortune,
Chris
Thank you both for fast responses.
I will definitely try both tweaks and post the results 🙂
JJ ECC83 uses Spiral Wound Filament Wire . . . one time up, and one time down, inside the cathode.
Some other ECC83 use non-spiral wound filament wire (straight wire), up and down many times inside the cathode.
Some other ECC83 use non-spiral wound filament wire (straight wire), up and down many times inside the cathode.
You have just shown that JJ ECC803 works better in your amp. Then i would advice you to keep
using JJ tubes.
