• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

My amp is motorboating, improve it with b+ regulator ?

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I don't think the spikes you pick up are 192 kHz. That should not come through like that. That looks more like RF interference. Is it present with zero input signal? Does its signature change when you change the sampling rate of the sound card?

Try making some scope shots of the amp output with its input grounded. Also, ensure that you use the ground clip on the scope probe rather than the grounding plug on the front of of the o'scope. It's quite likely that the smearing of the trace that you see is caused by poor grounding of the o'scope probe (measurement error) or supply ripple feeding through to the output. If it's caused by supply ripple, then a good B+ regulator would eliminate this.

Recall that inductance is proportional to loop area. Hence, if the loop area formed by the input impedance of the o'scope, the probe cable, probe, circuit under test, and back through the measurement ground is large, you'll have a lot of inductive pick-up. Perfect for 50/60 Hz to get in.

Nice scope, by the way. I remember using those in college... :)

~Tom
 
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Thanks guys,i am glad you haven't lost interest:)

Tom ,
I think the spikes are introduced by a cheap signalgen/supply on my bench:mad:

i followed your recomendation with the wiring and i took a pic of the trace on amp output with input grounded, set to 10mV,5uS (and the signalgen switched off.)

IMG_7503.jpg



maybe the blurry lines on my previous posts are leading in the wrong direction.
I also need to explain the sound i am chasing.
its an audible noise produced by the output tube of the amp, i called it squeeging before. Possibly this is the wrong term for it, sorry about my english here.
its more like a whistle produced by the tube even if only a resistive load is connected. it varies with the frequency i feed from 8khz to 17khz, and it varies with the volume setting. since it is also audible when i feed the signal directly into the driver stage i am thinking now its either produced in the driver or output stage of the amp.
 
Your scope shot looks pretty decent. The last bit of trace blur may be from local FM radio transmitters. You can investigate by reducing the time scale.

On my 400 MHz scope I get about 20 mVpp of 91.7 MHz from a local transmitter. Hence, I tend to have the 20 MHz bandwidth limiter enabled when I perform low-level measurements.

~Tom
 
remove R56-R61 and the 1n4007's out of the output circuit.

i tried this before, didn't change anything.
i also removed C31.
still the same problem.
i looked at the powersupply circuit again and simplified the heater circuit.
i doesnt change the sound i am hearing though:mad:
all the schematics are attached so everyone can see it as built.
 

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