Had a 5150 2-12 come in for a simple retube and what I thought might happen did.....redplating with the replacement tubes. Given the arrangement they chose, there is no upward (voltage) adjustment. You can go down if need be. I decided to omit the stock setup and pull bias from the HV winding via 100k 1w and just tapped that into the existing circuit (omitted c65 and the 100k runs to cr22...cr23 was clipped out. Now I can get plenty of AC voltage at the diode, around 190v. But no DC where it should be.
For those not familiar with this circuit, there's nothing to it. After the diode passes negative ac cycles, there's a 220u cap to gnd, series r (was 470r) which was changed to 15k, on to another 200u to gnd and the other divider R (which was changed to 22k fixed and 100k trimmer in series) to gnd.
http://music-electronics-forum.com/a...2909-5150c.gif
So ahh....what gives? Its just a variation of what they were doing to begin with and a pretty std circuit. Just for reference, the bias circiot worked as intended before the changes, so the diode is good.
For those not familiar with this circuit, there's nothing to it. After the diode passes negative ac cycles, there's a 220u cap to gnd, series r (was 470r) which was changed to 15k, on to another 200u to gnd and the other divider R (which was changed to 22k fixed and 100k trimmer in series) to gnd.
http://music-electronics-forum.com/a...2909-5150c.gif
So ahh....what gives? Its just a variation of what they were doing to begin with and a pretty std circuit. Just for reference, the bias circiot worked as intended before the changes, so the diode is good.
Comment