Home Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

Re: Back to the Drawing Board....

I put the bypass cap back in and I took out the preamp and put in the shorting plugs. It made the noise again. It seems to take about 3-5 minutes for it to get to that point. I will check and see if I have a 6.3 volt tranny in one of my junk boxes. I measured the bias as -130 vdc by putting the positive probe of my DVM on the grid of the 845 and the negative probe on one of the filaments of the 845. Is that the right way to measure it? Is that too high a bias voltage? My B+ is running about 785vdc right now because I am only using one 845. The filaments on the 845 are 10vac with a center tap to ground through a 1k/25w resistor. I am not sure what you mean by is the supply grounded properly. I am using a variac to bring everything up. It is plugged into a multiple outlet which is plugged into a grounded wall outlet. I am using a ground buss on top of my bread board chassis that I hook the ground from the variac to. The other two wires go to the primary terminals on the power tranny. All ground connections from the bread board components go to the ground buss on the bread board chassis. I have used this same set up for bread boarding many other amps and have had no trouble with it, there is always a first time for everything.
Vince


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