bet you guys guys thought i had given up!!
on the contrary, some semblance of a victory:
powered up by bypassing the mains selector - DC voltages looked good everywhere. im not 100% exactly the range i should be seeing on all the various pre-amp tubes, but suffice it to say all the plates had high-ish voltages and all the cathodes had low-ish voltages, except for the PI which had about 80VDC at the cathodes. power tube voltages looked good, with about 450V on the plates and -50 on the grids with the bias turned all the way down (with tubes pulled at this point) - i put in a lil sine wave and traced it through and, sure enough, on the output of the PI i had about 80V p-p from about 100mV on the way in. now the preamp tube configuration in this amp is new to me, and the order is not intuitive (the PI is the second tube in....even though on the scheme its V5....!), so i might end up having to come back here if there is a problem.
popped the tubes in and checked the see if the bias circuit was working and sure enough it was! i had the light bulb limiter in at this stage and it started to get brighter as i increased the control grid bias voltage. that seems right - tubes are actually pulling current so the amp must supply it. wondering if even trying to bias them with a limiter in-line is a dumb move, but i am still nervous something is going to blow up.
anyway, put in sound and sound came out! (i was worried the OPT might have been bad)
so ill try it out tomorrow with a guitar and we'll take it from there.....
on the contrary, some semblance of a victory:
powered up by bypassing the mains selector - DC voltages looked good everywhere. im not 100% exactly the range i should be seeing on all the various pre-amp tubes, but suffice it to say all the plates had high-ish voltages and all the cathodes had low-ish voltages, except for the PI which had about 80VDC at the cathodes. power tube voltages looked good, with about 450V on the plates and -50 on the grids with the bias turned all the way down (with tubes pulled at this point) - i put in a lil sine wave and traced it through and, sure enough, on the output of the PI i had about 80V p-p from about 100mV on the way in. now the preamp tube configuration in this amp is new to me, and the order is not intuitive (the PI is the second tube in....even though on the scheme its V5....!), so i might end up having to come back here if there is a problem.
popped the tubes in and checked the see if the bias circuit was working and sure enough it was! i had the light bulb limiter in at this stage and it started to get brighter as i increased the control grid bias voltage. that seems right - tubes are actually pulling current so the amp must supply it. wondering if even trying to bias them with a limiter in-line is a dumb move, but i am still nervous something is going to blow up.
anyway, put in sound and sound came out! (i was worried the OPT might have been bad)
so ill try it out tomorrow with a guitar and we'll take it from there.....