CCS pulsing oscillation problem

[optimationman]

I have a 10m45 CCS feeding a 6922. Everything is working and the sound is good. I have been using this simple tube setup for a tube out for a tda1541 based cd player. The circuit was posted by ThoestonL, a single tube section for each channel. My problem is that although I have been enjoying the system, I discovered an interesting phenomenon. With no signal present and all other equipment off, there is a high freq "burst" on the output side of the 10m45 every 10sec(difficult to see the sinusoidal portion, constant amplitude oscillation is obvious). Then the trace is flat for the next 10sec. The duration of this burst is very difficult to estimate(maybe 1/4sec), and was difficult to photo. I installed a mains filtering system, and turn off all the other breakers in the house, but still the burst is there. No other equipment is on. I have the 1k stopper in place, the bias is controlled with a 100ohm dale and 500 ohm trimmer. The tube operation point is 65v and 12ma. All is very stable with no other oscillation, just the 10sec interval burst. I increased the applied voltage to the 10m45 from 120 to 145dcv with no change. The power supply is a simple rcrcrcrc with a smooth ripple free trace. I am using a single 10m45 per side of the tube. Any Ideas?

[optimationman]

Forgot to mention, I also have tried 6dj8s, e188cc etc. Same problem

[DigitalJunkie]

Could it possibly be coming out of the DAC?

Perhaps it's noise from the motors,etc. in the CD player? Lens trying to focus,to see if there is a disc present,or something?

What happens if you disconnect the tube stage from the DAC output? is it stable?

I don't know,just a couple thoughts.

[optimationman]

Thanks for the input. The CD player is off, as is all other equipment. I have disconnect the output and the input just now, same pulse!

[optimationman]

One more item. I have change the current flow from 7ma to 17ma, No change, still the burst!

[Defiant]

Post a schematic. It sounds like you inadvertently built a sort of relaxation oscillator.

Is the 1k stopper on the MOSFET?

[optimationman]

I will post the schematic tomorrow morning. Yes, the 1k is on the gate. Found the original schematic. I used the CCS instead of the 160H choke. I also left out the freq compensating parts, but built it about the same.

[SemperFi]

So is this a separate DAC and when the input is disconnected from the CDP u get this?
I would guess it's some logic at work, but if its disconnected it must be something else.

I see no grid stopper! A MUST with these tubes. Also the bias is extremely high but that may be intentional? There must be some grid current flowing? Is that to load the current output DAC properly?

If grid stopper doesnt help, perhaps you should include the freq-compensation.

[Blaireau]

Beware of the 0.15mH coil! Just disconnect it for a while, and check if the spurious has disapeared. As mentioned previously, the missing grid stopper can also be responsible of your problem.

[optimationman]

Thanks for the food for thought. I was thinking that the high freq compensation circuit could(boosts the high freq) be left out(no inductor). That is the network connected to the grid was to correct the high freq roll of due to NOS operation of the tda1541. I can't hear that high loss anyway, and I just placed a 50 ohm resister in it's place to make the I/V conversion. I will add a 1k grid stopper this morning to see if that stop this periodic oscillation. Keep in mind that this oscillation occurs for just a moment, and has a 10 sec quiet time between bursts.