Its been about a year since I built a Triode ST 70 kit, and along with a PAS-3 that I rehabbed, its been fantastic and scary reliable. I have been tinkering with it a bit as of late, and have some nagging issues with it.
The first one is a very slight hum when anything is hooked up to the PAS other than my iPod (or nothing at all). I'm reasonably sure this is some sort of ground loop issue, as when I ran the ST off of my solid state receiver's preamp out, I got the same hum. When I have the PAS hooked up with nothing or the iPod connected to it, it is whisper quiet. The second I hook up just one channel of a device that is plugged into the wall, I get the hum, even with the volume turned all the way down. When I built the amp, I left the ground terminal disconnected in the IEC socket. The PAS has the stock 2-prong power cord without ground. I tried grounding the IEC socket in the ST to chassis and it made the hum much, much worse. It also hums even when the PAS is powered off.
My second issue is I wanted to swap out my phase splitter tube on the Triode EF86 board to a 6N6P that I got off of ebay for another project, just to see how they sound. Strangely, when I plug one into the socket, the heater doesn't come on. Do I need to rewire the heater circuit to get these tubes to work?
Also, after killing another 5AR4 rectifier tube by firing the amp up while the tubes were warm, I decided that it might be wise to add some diodes under the rectifier socket and find a bit more robust tube. I have a 5U4BG that I got with a bunch of other tubes. Can I use this with the diodes and not have any issues? If worse comes to worse I do have a Webber Copper Cap that has been faultless, but I like the look of tubes.
Thanks in advance to anyone who has any input. DIYT is a wealth of information.