hembrook wrote:I tried powering it up, and while the rectifier powered up, the rest of the amp did not, so I am back to the beginning. No heat on the 6SL7 or the 6B4Gs. Maybe the heater windings on the tranny canceled each other by phase? I dunno. Its all in pieces on my workbench now.
hembrook wrote:I just tied off the wires from the 3rd heater winding, and soldered the sockets back to the board. I fired it up and I still get a mechanical hum from the chassis. With the 6B4G(ish) tubes in it hums thru the speakers, but with the 6A5Gs in it is quiet thru the speakers, tho the chassis still hums.
separks wrote:How quiet is this mechanical hum, since some is normal?
separks wrote:I remember us talking about the different wiring setups for the 6B4G and 6A5G. Do you have the UX4 socket wired up standard?
hembrook wrote:separks wrote:How quiet is this mechanical hum, since some is normal?
I am going thru 95db or better speakers, so there is some hum in the speaker. I guess I need to get/learn to use and oscilloscope.separks wrote:I remember us talking about the different wiring setups for the 6B4G and 6A5G. Do you have the UX4 socket wired up standard?
6A5G is pin-compatible with the 6B4G and is octal. I wired it standard, so I can also use 6B4Gs in the circuit (which hum considerably more).
separks wrote:
Even with my 102dB horns, my GSG is one of my quietest amps - its totally silent. I think it might be time to put in hum pots. You could use two 100 ohm, 3W pots. No need to chassis mount them at first, while testing. You can remove the 47 and 51 ohm resistors and mount it with resistor leads from junkbox resistors. The wiper goes to where the 47 and 51 ohm resistors meet.
separks wrote:
BTW, sorry if I've asked this before, Robert, but are you using a safety ground to the chassis?
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