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This Warwick Tubepath 10.1 is in pretty clean condition, though it may have been dropped (the front panel is badly bent).
When turned on, there is an immediate buzz, even before the protection relays kick in, sounds like it's coming from the toroidal PT. Then, after warming up for 30 seconds or so, it begins to motorboat (see video).
The preamp is working fine--audio at the headphone jack is OK.
I replaced all three tubes to rule them out. The motorboating is not audible on the headphones out, nor the line out, only the speaker out.
Aside from the main filter caps, any other possibility for the motorboating come to mind?
warwick_hdb-electronic_tube-path_10.1_sch.pdf
When turned on, there is an immediate buzz, even before the protection relays kick in, sounds like it's coming from the toroidal PT. Then, after warming up for 30 seconds or so, it begins to motorboat (see video).
The preamp is working fine--audio at the headphone jack is OK.
I replaced all three tubes to rule them out. The motorboating is not audible on the headphones out, nor the line out, only the speaker out.
Aside from the main filter caps, any other possibility for the motorboating come to mind?
warwick_hdb-electronic_tube-path_10.1_sch.pdf