Hi,
I want to measure the noise the final tubes make in a PP stage. In other words, disconnected from the driver stage. With nothing connected to the finals G1 (except the negative voltage through a 100K resistor) I can hear some noise. With UL the noise is louder than in triode mode, but the nature / sound of the noise is similar.
I tried shorting both G1’s with a capacitor (0.15 uF) to ground. This resulted in quite loud pops (pop pop pop, every second) from the speaker. Then I tried both G1’s connected to each other with these capacitors, but this resulted in a high tone screaming from the speaker. There is no NFB in the amplifier, only UL mode when selected.
Do driving grids pick up noise when not shorted for AC?
I will hookup my spectrum analyzer tomorrow to get a beter view on what’s happening.
Regards, Gerrit
I want to measure the noise the final tubes make in a PP stage. In other words, disconnected from the driver stage. With nothing connected to the finals G1 (except the negative voltage through a 100K resistor) I can hear some noise. With UL the noise is louder than in triode mode, but the nature / sound of the noise is similar.
I tried shorting both G1’s with a capacitor (0.15 uF) to ground. This resulted in quite loud pops (pop pop pop, every second) from the speaker. Then I tried both G1’s connected to each other with these capacitors, but this resulted in a high tone screaming from the speaker. There is no NFB in the amplifier, only UL mode when selected.
Do driving grids pick up noise when not shorted for AC?
I will hookup my spectrum analyzer tomorrow to get a beter view on what’s happening.
Regards, Gerrit
Short the coupling capacitor to GND (disconnect it from the phase inverter before).
BTW the final tube has no noise 😉
BTW the final tube has no noise 😉
That’s exactly what I did and got the quite loud popping noise….
Without AC shorting I can hear some noise and can hear the tube internals heating up. Very soft ticking and I can hear through the tubes (KT150) as they are slightly microphonic. Ticking on the the tube’s glass is audible too. The KT150’s need at least one minute to go from 0 to 100 mA for each tube. With a plate voltage of 600 VDC that’s 120 Watts of heat…
Regards, Gerrit
Without AC shorting I can hear some noise and can hear the tube internals heating up. Very soft ticking and I can hear through the tubes (KT150) as they are slightly microphonic. Ticking on the the tube’s glass is audible too. The KT150’s need at least one minute to go from 0 to 100 mA for each tube. With a plate voltage of 600 VDC that’s 120 Watts of heat…
Regards, Gerrit
I’m using a speaker. I haven’t used a grid stopper for this tube, but I may try this tomorrow.
Regards, Gerrit
Regards, Gerrit
Well, I do hear some noise, and it’s not a specific frequency or frequency band. I will compare with the other channel to be sure.
I do have a small resistor in the UL G2 lead. HT is 600 VDC regulated. In fact all voltages are regulated, except 6.3V AC for the final tubes. Drivers are on DC heating and fed from a 400 VDC regulated supply.
I don’t use NFB, but UL is a sort of feedback too of course. Today I connected the G1’s to the mosfet follower (capacitor coupled) and the noise remains unchanged. Still work in progress…
Regards, Gerrit
I do have a small resistor in the UL G2 lead. HT is 600 VDC regulated. In fact all voltages are regulated, except 6.3V AC for the final tubes. Drivers are on DC heating and fed from a 400 VDC regulated supply.
I don’t use NFB, but UL is a sort of feedback too of course. Today I connected the G1’s to the mosfet follower (capacitor coupled) and the noise remains unchanged. Still work in progress…
Regards, Gerrit
Today I connected both G1’s to the MOSFET follower’s of the driver circuit. Both channels are now very, very silent.
I connect the amplifiers output to another (Sony) amplifier’s input (directly… only with 2 limiter / safety diodes accross the wires). With the Sony’s volume control set to maximum, I can hear very light noise from the speakers. I use this setting only to get an audible signal, so I can hear hum, noise, microphonics, etc..
Regards, Gerrit
I connect the amplifiers output to another (Sony) amplifier’s input (directly… only with 2 limiter / safety diodes accross the wires). With the Sony’s volume control set to maximum, I can hear very light noise from the speakers. I use this setting only to get an audible signal, so I can hear hum, noise, microphonics, etc..
Regards, Gerrit