Thanks for the repair video. It makes me think I should get around to repairing my 7854. It has gotten to the point where the processor doesn't seem to work correctly until the scope has warmed up for an hour or two. Before that you can't clear the initial "self test complete" message, and can't capture a trace or view trace memory. Probably a cap problem of some sort. I just powered my 7834 on for the first time in probably 5 years, and very annoyingly it seems to have an HV problem. All of the readouts are completely out of focus, and possibly (I'm not sure) the raster might be a little smaller than it should be. I don't have plugins in the mainframe, so can't check the trace, but I'm sure it would be out of focus too. Probably another old cap problem. :-( A decade or so back this scope had a problem where it wouldn't power up, and it turned out to be a shorted small tantalum cap on the backplane board the plugins plug into.
Eddie VanHalen used a variac on the first album. He'd run the amps' voltage to around 140 vac, and he said the tubes would wear out in about 2 hrs, and the (very expensive Marshall) amps in 12, or something thereabouts.
Filament life is proportional to the 13th power of the applied voltage. That's a big number. Assuming the amp was rated for 125V (somewhat unlikely), 140/125 = 1.12; 1.12^13 is about 4.4, so the tubes should only die 4 or 5 times sooner than normal. If I assume the amp was rated for 115V (more likely, I suspect) 140/115 = 1.22; 1.22^13 is about 13, so the tubes should last 1/13th of their normal life. If the amp was rated for 110V instead of 115, the tubes would die about 23 times sooner than normal. All of those times should be well beyond 2 hours, but there may other factors at play, like blasting the coating off the filaments, which would drastically reduce the tube output when it happened.
I wonder what Tek would have charged if this was sent back for factory repair? They would have likely swapped pcbs . No more HV in scopes now. Just a few chips on one board.
There’s only one name in lab oscilloscopes and it's this one. Oh. I really don’t like non-CRT ‘scopes but they are compact. Perhaps the latest type are better. I’m ‘old School’. 🫢😉
Thanks for the repair video. It makes me think I should get around to repairing my 7854. It has gotten to the point where the processor doesn't seem to work correctly until the scope has warmed up for an hour or two. Before that you can't clear the initial "self test complete" message, and can't capture a trace or view trace memory. Probably a cap problem of some sort.
I just powered my 7834 on for the first time in probably 5 years, and very annoyingly it seems to have an HV problem. All of the readouts are completely out of focus, and possibly (I'm not sure) the raster might be a little smaller than it should be. I don't have plugins in the mainframe, so can't check the trace, but I'm sure it would be out of focus too. Probably another old cap problem. :-( A decade or so back this scope had a problem where it wouldn't power up, and it turned out to be a shorted small tantalum cap on the backplane board the plugins plug into.
Eddie VanHalen used a variac on the first album. He'd run the amps' voltage to around 140 vac, and he said the tubes would wear out in about 2 hrs, and the (very expensive Marshall) amps in 12, or something thereabouts.
Filament life is proportional to the 13th power of the applied voltage. That's a big number. Assuming the amp was rated for 125V (somewhat unlikely), 140/125 = 1.12; 1.12^13 is about 4.4, so the tubes should only die 4 or 5 times sooner than normal.
If I assume the amp was rated for 115V (more likely, I suspect) 140/115 = 1.22; 1.22^13 is about 13, so the tubes should last 1/13th of their normal life. If the amp was rated for 110V instead of 115, the tubes would die about 23 times sooner than normal.
All of those times should be well beyond 2 hours, but there may other factors at play, like blasting the coating off the filaments, which would drastically reduce the tube output when it happened.
I wonder what Tek would have charged if this was sent back for factory repair? They would have likely swapped pcbs . No more HV in scopes now. Just a few chips on one board.
wow
hello bob
First!!!
There’s only one name in lab oscilloscopes and it's this one. Oh. I really don’t like non-CRT ‘scopes but they are compact. Perhaps the latest type are better. I’m ‘old School’. 🫢😉