Based on earlier measurements (of just B+ and the anode voltage of the Aa) there had to be grid current flowing (see post #17). In my view it would be a good thing to make that stop, no matter if that was the cause fo the hiss or not.
... as my second sentence says.
Banpuku random filament pint voltage measuring leads nowhere if concrete operating point not available.
If he don't want to measure anode current, only anode-virtual cathode and virtual cathode-ground voltage measuring helps.
Banpuku random filament pint voltage measuring leads nowhere if concrete operating point not available.
If he don't want to measure anode current, only anode-virtual cathode and virtual cathode-ground voltage measuring helps.
progress:
1. shorting grid to ground did nothing. hiss still present.
2. connected a 3.6V battery to filaments. Hiss is gone. dead silent.
I am using Tentlabs on the VT62 tubes as well. No problems there. The hiss is occurring on both monoblocks using 4 different Aa tubes. So, its not a tube problem. Output voltage from the Tentlabs is rock solid. I can set it to any voltage up to 5.6V. Currently set at 3.8V according to tube spec.
It would be hard to believe that both of the driver tube TentLab supplies are bad. Makes no sense. I also used these same TentLabs supplies with the same Aa tubes about 3 weeks ago and had no issues. The only thing that has changed is the output tube. Replaced the EML 50 with the VT62.
1. shorting grid to ground did nothing. hiss still present.
2. connected a 3.6V battery to filaments. Hiss is gone. dead silent.
I am using Tentlabs on the VT62 tubes as well. No problems there. The hiss is occurring on both monoblocks using 4 different Aa tubes. So, its not a tube problem. Output voltage from the Tentlabs is rock solid. I can set it to any voltage up to 5.6V. Currently set at 3.8V according to tube spec.
It would be hard to believe that both of the driver tube TentLab supplies are bad. Makes no sense. I also used these same TentLabs supplies with the same Aa tubes about 3 weeks ago and had no issues. The only thing that has changed is the output tube. Replaced the EML 50 with the VT62.
Now Mr TentLab is on diyaudio so why not send him a email. Since you only need DC on the heaters there is a solution.
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Try 100nf-1uF from each heater connection to ground - the biggest ceramic or film you have. They don't quote the noise but it would get amplified by you input tube. Its not its bad its just noisy.
Available versions
Currently 3 hardware versions are available:
• Low noise version, output currents up to 1A. These typically serve small size triodes to be used as line stages. Output noise is 26dB lower compared to the standard version. Often used in conjunction with type 26 tube, integrated heatsink.
• Standard version, output currents up to 2.5A. These typically serve small and medium size triodes up to output tubes like 300b and 2A3, and have an integrated heatsink.
• Output currents up to 5A. These will suit the beefy types like 211, 813, 845 and SV572 and have a bigger heatsink.
Currently 3 hardware versions are available:
• Low noise version, output currents up to 1A. These typically serve small size triodes to be used as line stages. Output noise is 26dB lower compared to the standard version. Often used in conjunction with type 26 tube, integrated heatsink.
• Standard version, output currents up to 2.5A. These typically serve small and medium size triodes up to output tubes like 300b and 2A3, and have an integrated heatsink.
• Output currents up to 5A. These will suit the beefy types like 211, 813, 845 and SV572 and have a bigger heatsink.
If you used a mains toroid you could get coupling from the mains all the way through the supply to the filament (cathode). At 20uV the gain of the first stage may be 20-50 and the second 20 brining the noise to 20mV maybe just audible. Its also possible the regulator is oscillating generating much higher levels.
Baudouin0 - connecting a 0.68uF cap from each pin to ground helped slightly, but the hiss is still there. Just slightly help.
Mains are not toroid.
Mains are not toroid.
Yes, toroidal PTs can pass a lot of noise into the filament. Screened types (Antek, Canterbury, Toroidy audio types) are good though.
Check appliances connected to nearby wall sockets for Line to DC converters - TV, computer, LED lighting strips. Turn them off. Turn of any nearby lighting, as a check.
Bypass the bias diode with 470uF + 1uF film is another test for PT leakage problems.
Otherwise, contact Guido.
Check appliances connected to nearby wall sockets for Line to DC converters - TV, computer, LED lighting strips. Turn them off. Turn of any nearby lighting, as a check.
Bypass the bias diode with 470uF + 1uF film is another test for PT leakage problems.
Otherwise, contact Guido.
So, if you pull out Aa tube and hiss gone, the cause -probably- is the first stage.
Why not try temporary heating Aa filament with battery?
If the hiss gone, filament supply the reason of this.
Why not try temporary R//C in the cathode ... together with virtual cathode (two 33R resistor from filament pins)?
Why not try temporary heating Aa filament with battery?
If the hiss gone, filament supply the reason of this.
Why not try temporary R//C in the cathode ... together with virtual cathode (two 33R resistor from filament pins)?
euro21 - please see post #43. "connected a 3.6V battery to filaments. Hiss is gone. dead silent."
Team - thanks for all the input. I received a reply from Guido regarding the Tentlab filament supplies. "The Aa draws 0,5A which is OK for this filament supply. However, when you use it it to feed the driver stage, hiss can occur. Therefore we developed the low noise version."
So, I need to go with a lower noise version. Or, I may use my Coleman filament supplies.
I want to take time to thank each of you for replying. Very helpful. Also of special note, I cease to be amazed at how kind and professional Rod Coleman is. He willingly tried to help knowing that his product was not being used. I have dealt with Rod several times in the past and he is a quintessential gentleman and professional. His products, along with Guido's, are highly recommended. Thanks to both.
So, I need to go with a lower noise version. Or, I may use my Coleman filament supplies.
I want to take time to thank each of you for replying. Very helpful. Also of special note, I cease to be amazed at how kind and professional Rod Coleman is. He willingly tried to help knowing that his product was not being used. I have dealt with Rod several times in the past and he is a quintessential gentleman and professional. His products, along with Guido's, are highly recommended. Thanks to both.
I had not considered how noise the regulator could be. A MIC29152W (which is what I would have used) comes in at over 300uV. Maybe avoid DHT for pre-amps for me.
MIC 29xx series parts do measure more noise than other ICs, but none of them make a good filament regulator.
The self-noise of my V8 or V9 filament regulator is below the noise floor of a Mic amp, which is 56nV/rtHz even at low frequency.
The V8 version, for 500mA, built with the ordinary Raw DC recommendations, has a spot noise at 100Hz of about 2µV, and even that can be eliminated with the a little more C or R.
You can make silent DHT preamps with these, even with filament bias! See the 26 preamp thread, or the 4P1L preamp thread.
The self-noise of my V8 or V9 filament regulator is below the noise floor of a Mic amp, which is 56nV/rtHz even at low frequency.
The V8 version, for 500mA, built with the ordinary Raw DC recommendations, has a spot noise at 100Hz of about 2µV, and even that can be eliminated with the a little more C or R.
You can make silent DHT preamps with these, even with filament bias! See the 26 preamp thread, or the 4P1L preamp thread.
Even with floating heater supply, you have to make sure to use a cap bypass the center point of the heater to ground.
One time, I tried a cheap 12v switch power supply (the one to power Modem) with dynaco sca-35, which has 150 gain on the output stage. Hiss is not a problem.
One time, I tried a cheap 12v switch power supply (the one to power Modem) with dynaco sca-35, which has 150 gain on the output stage. Hiss is not a problem.