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In Reply to: RE: Signal ground is never connected to Chassis posted by dbishopbliss on April 18, 2008 at 17:41:40
First, the question. What happens to the green filament winding once it gets to the PC board? Does it get turned into DC, or left as AC to run the tube filaments?
OK, now, before you tie the center-tap (and therefore, the circuit ground) to the chassis ground, perhaps a few more readings are in order.
First, unplug the amp. Then, take a DC voltage reading from B+ to circuit ground. Plus to minus on one of those big filter caps will do, for instance. If you have a clip lead or another way of safely connecting the black lead of your meter to circuit ground (not chassis), that would be the thing to do. Before the next readings I want you to take, I would like to make sure that there is no charge left in the caps, so zero Volts DC is what I'm hoping for here.
If you still see high voltage, you will need to bleed it off to get the voltage down to 0.
Once you've got O VDC, then pull the 5AR4, and set it aside. There are two pairs of wires coming from the power transformer going to the 5AR4 socket. Take an Ohm reading from each of these pins on the socket to chassis ground.
The reason I am suggesting these additional steps is that, when the circuit ground of the amp got connected to chassis ground through the Foreplay, the amp blew a fuse. I think it would be a good idea to see if we can find some reason that that happened before connecting those two points together in the amp.
I apologize to you and Doc for butting in on your thread, but it got my curiosity going! So, if its OK with you, I'd be interested in your results.
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