Ok this is driving me nuts. I installed an Octal board in my st70 and it sounded great for about 7hrs of use then then volume on the right side went to almost nothing. I have verified the Inputs, tubes, solder connections, resistors at the sockets, voltages are all good. Where do I look next? Whats the best way to verify that the cap on that side is good? need help please.
4 posters
vta st70 low volume right side
Its a toaster- Posts : 3
Join date : 2016-09-30
Roy Mottram- Admin
- Posts : 1839
Join date : 2008-11-30
more likely a flakey solder connection than a bad capacitor, but you could easily swap the two output capacitors on side side to the other side and see if the problem follows.
Its a toaster- Posts : 3
Join date : 2016-09-30
I went back and re soldered the whole right side. no change. tested resisters on the board and they measure correct. rechecked all grounds. going to try cap swap after I get everything discharged. any other ideas?
Peter W.- Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA
Its a toaster wrote:I went back and re soldered the whole right side. no change. tested resisters on the board and they measure correct. rechecked all grounds. going to try cap swap after I get everything discharged. any other ideas?
Did you swap the output tubes?
Check the drivers? If ones side of a common dual-triode is weak - there you are.
Do you have the capacity to check tubes?
peterh- Posts : 1832
Join date : 2012-12-25
Location : gothenburg, sweden
Swapping the outputs as suggested would tell more. It's a matter of rerouting the cap from the
board AND the feedback from the output tranny.
If the problem changes side the fault is at the board, if the problem stays it's the output tranny or
the tubes that is the cause.
board AND the feedback from the output tranny.
If the problem changes side the fault is at the board, if the problem stays it's the output tranny or
the tubes that is the cause.
Peter W.- Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA
peterh wrote:Swapping the outputs as suggested would tell more. It's a matter of rerouting the cap from the
board AND the feedback from the output tranny.
If the problem changes side the fault is at the board, if the problem stays it's the output tranny or
the tubes that is the cause.
Hmmmmmm....
I would think that if the problem follows the tubes, then the tubes might be at fault....
Or am I missing something?
peterh- Posts : 1832
Join date : 2012-12-25
Location : gothenburg, sweden
No, you are not missing anything.Peter W. wrote:peterh wrote:Swapping the outputs as suggested would tell more. It's a matter of rerouting the cap from the
board AND the feedback from the output tranny.
If the problem changes side the fault is at the board, if the problem stays it's the output tranny or
the tubes that is the cause.
Hmmmmmm....
I would think that if the problem follows the tubes, then the tubes might be at fault....
Or am I missing something?
But moving two connections ( swapping side) will test powertubes AND OT without needing to
pull the tubes from the sockets. And forget tubetesters, they won't help here.
Peter W.- Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA
>>And forget tubetesters, they won't help here.<<
On the tube-testers: If one of the driver tubes is faulty, specifically a dual-triode, as in the Whoville Christmas tree that does not 'light on one side', it could explain low volume. Similarly, a tube with a shorted element.
On the tube-testers: If one of the driver tubes is faulty, specifically a dual-triode, as in the Whoville Christmas tree that does not 'light on one side', it could explain low volume. Similarly, a tube with a shorted element.
peterh- Posts : 1832
Join date : 2012-12-25
Location : gothenburg, sweden
Peter W. wrote:>>And forget tubetesters, they won't help here.<<
On the tube-testers: If one of the driver tubes is faulty, specifically a dual-triode, as in the Whoville Christmas tree that does not 'light on one side', it could explain low volume. Similarly, a tube with a shorted element.
Yeh Yeh,
testing with another "known good" tube takes seconds and don't involve a tester.
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