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I am building an amp using 3 stages:
1st stage-ECC99 direct coupled ---> 2nd stage ECC99 ---> RC coupled 300B
But my OPT 2nd winding show this strange look.(attached picture)
Question:
(1) What is cause for those Spike, (short spike pluse, they generate Deeeeee sound, I use AC HT
(2) When direct couple ECC99 for 2nd stage, do I have to elevate the HT voltage by using votalge divider and a hum bypass cap. Right now I only short one leg of the AC HT on ground.
(3) When ground short the 1st stage ECC99, the noise from 2nd winding seem OK, but when it was left open (with 100K grid leak R to ground for 1st stage ECC99). There is a huge oscillcation problem on the ECC99'grid (around 5mV high freq oscillation).
The (3) is the major problem, any clue you may suggest to look into ?
Regards,
Follow Ups:
Try a 1K carbon on the plate as a potential cure.
I am building an amp using 3 stages:
1st stage-ECC99 direct coupled ---> 2nd stage ECC99 ---> RC coupled 300B
But my OPT 2nd winding show this strange look.(attached picture)
Question:
(1) What is cause for those Spike, (short spike pluse, they generate Deeeeee sound, I use AC HT
(2) When direct couple ECC99 for 2nd stage, do I have to elevate the HT voltage by using votalge divider and a hum bypass cap. Right now I only short one leg of the AC HT on ground.
(3) When ground short the 1st stage ECC99, the noise from 2nd winding seem OK, but when it was left open (with 100K grid leak R to ground for 1st stage ECC99). There is a huge oscillcation problem on the ECC99'grid (around 5mV high freq oscillation).
The (3) is the major problem, any clue you may suggest to look into ?
Regards,
HI Eric,
In the first photo it has 50Khz. It should be oscialltion there.
In 2nd photo, What is the frequency of the spike??
BTW, please show us your circuit.
Wilson
HI Eric,
In the first photo it has 50Khz. It should be oscialltion there.
In 2nd photo, What is the frequency of the spike??
BTW, please show us your circuit.
Wilson
The waveform is asymmetrical as well.
Probe the circuit from the first stage on all points and go forward.
Try gnd and ungrounding the probe. 1x-10x if possible(safe).
Cheers!
> > Probe the circuit from the first stage on all points and go forward.
With grounding the Grid of 1st stage or left open ?
Regards,
The ECC99 is a very high transconductance tube. Do you have proper grid stop resistors in place?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I put 1.5K Grid Stopper in every grid for each tube.
Additional info:
1. ECC99 is in AC Filament, with one AC leg grounded. 300B is in DC filament.
2. The output from Power supply seem good, very little ripple, no spike
3. Power supply is: 1N5408 SS diode(full wave) -> 220uF Cap -> 5H L -> 220uF Cap (connected to 300B stage) -> 750 ohm R -> 14H L(connected to 2nd stage ECC99) -> 24K R (connected to 1st stage ECC99)
For the decouplling Cap, I put each decoupling cap closed to each ECC99 stage already
4. with 1st stage grid grounded, the noise is 1mV measured in 2nd OPT winding. without grounding the grid for 1st stage, the grid of 1st stage would appear as much as 10mV P-P irregular ultra high freq oscillation.
5. For the 4. measurement, there is no any cable soldered from the grid of 1st stage yet.
It seems I have followed the cook book but don't know why it come up like that.
Regards,
3. Power supply is: 1N5408 SS diode(full wave) -> 220uF Cap -> 5H L -> 220uF Cap (connected to 300B stage) -> 750 ohm R -> *75uF Cap* -> 14H L-> *22uF cap*(connected to 2nd stage ECC99) -> 24K R -> *10uF cap* (connected to 1st stage ECC99)
I put decoupling cap 22uF and 10uF very closed to ECC99 each stage already.
The resistor in series with the grid is a "grid stop resistor".
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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