Hi forum folk. First time caller, long time listener. Thanks in advance for any suggestions.
During this downtime, I built a version of Rob Robinette's Deluxe Micro using a bunch of old parts and a few new ones.
Fired it up today, and it's an awesome little amp.
*But during a post-trial voltage check, I metered between the heater circuit and the chassis, and saw about 150VAC....didn't check this during initial start up for some reason...
Not sure where this could be coming from, so I'm looking for some ideas.
When I measure across the heaters or pilot light, I see +/- 6V, as I would expect.
There are some deviations from Rob's posted schematic, but overall it's pretty close.
What's different:
no-name scrap heap PT
6X4 rectifier instead of EZ81
10uF filter caps
1R0 5W dropper in heater string
I bench checked the PT for shorts, then checked unloaded secondary voltages before i installed it.
They were:
Red/RW/Red: 325-0-325V
Blue/BW/Blue: 28-0-28V capped off
Green/Green: 7.3V
Yellow/Yellow: 7.8V capped off
No idea what current capacity it has, but the wiring and build are fairly stout. I hope/think it can handle this circuit.....PT warm after 30 min trial run, but not excessive heat by any means.
I don't do drawing programs, so I am attaching a cocktail napkin schematic of the power plant as built, can add pictures if anyone is willing to take a look.
So, to summarize my problem:
Any ideas what this 150VAC between heater circuit and chassis means?
Does it even matter?
I inspected every connection I made, nothing is shorted as far as I can tell.
The current draw through my Sencore unit is about 30mA at idle, creeps up a bit when the amp is pushed.
Here are the tube voltages at idle with 8R dummy load, no input signal @125VAc in:
6X4: pin 1 and 6: 327VAC, pin 7: 390VDC
12AU7: pin1,6: 337V, pin 3,8: 13.5V
12AX7: pin 1: 149V pin 3: 2.3V pin 6: 157V pin 8: 2.24V
Thanks again for any thoughts.
