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I am looking for an application which can be used to compare the small input signal (0 to 10mV) and drive/trigger a 115VAC relay. The requirement is that the relay is off from 0 to 4mV. Between 5 and 10mV, it will trigger the relay. After the relay is closed, it will open again when the input...

Felixc, yes I beleived it only happend with the function generator, but not 100% sure since the sound may mask the noise. I think one of the function generator might use switching power supply, except for the HP generator I am not sure if it has linear or switching. I note the HP generator...

Scott, you're thinking right in term of avoiding DC through out put tranny. The parafeed term has been a popular term in audio cirle. The topology and the term is not new. It has been described in Radiotron Designer's Handbook by F. Langford Smith I think even before I was born. The output...

Scotty, I don't think the output from signal generator is floating, but will double check on that tonight. Also I don't believe that output tranny is driven into saturation since the output tranny is the parafeed type; therefore there's no path for DC current to flow. Yes, it's a single end...

Comcokid, yes I am aware of the maganetic couple between the choke, transformer and other components in the amps, especially the tubes. They located far apart and don't think it's a concern. Also the power tranny and power supply chokes are potted type, except for the plate choke. I am not...

Yesterday, I tested it with a portable CD player. The sound comes out very good. I did not hear any type of distortion. The signal for both input and output also looked very clean on the scope. During the silence passage, you do not see anything on the scope as expected. I still do not...

Felixc, can you explain a little more in detail what you meant by magnetostriction noise from the transformer? The plate choke mentioned is the load of the 300B tube and couple to the output transformer with an output cap. I subsituted the plate choke with an identical one last night, but I...

The noise does not add to the output signal. Both input and output looked very clean and stable on the scope. With the dummy load I could hear the pitch also but it very low volume. It appears coming from the plate choke of the 300B tube, but not 100% sure. Everyone obviously hear it when hook...

Hi all, I just recently built my SE Tube amp with parafeed output transformer. Everything looked fine and as expected when I tested it with a 8 ohm resistor dummy load. However, as soon as I hook up to a speaker and crank up my signal generator, I heard a loud high pitch noise and the noise...