Tom, Dick & Harry
Of Tribute and Tom Waits
"All my friends are married/every Tom and Dick and Harry" – it was that song line by Tom Waits that inspired the naming of my midrange/tweeter amps. They are single ended mono blocks with a shared power supply per channel. What makes them kinda special are the many, many transformers and chokes. They were all custom made by Tribute and wound on exotic amorphous, permalloy or cobalt cores; only the power transformer uses pedestrian silicon steel.
Tom (top) is a "spud" design i.e. a one-tuber with a 6S45Pi. Since Tom is hooked to a Fostex 925 super tweeter with an efficiency of 108 dB/W/m, the approximately 800mW are plenty of juice. Tom uses fixed bias with the negative voltage connected to the input transformer's secondary.
Dick (bottom) is the midrange amp feeding a TAD TD4001 compression driver with an efficiency of 110 dB/W/m. I've decided on a very classic circuit with a 56 triode driver IT coupled to a 45. All cathodes are grounded, the bias voltage is connected to the secondary windings of the input and the interstage transformer.
Tom and Dick share a common power supply that goes by the name of Harry (not shown). B+ is rectified with a GZ34 (wonderful NOS with copper plates!); the grid bias is rectified with a HexFred bridge. B+ is LCLC filtered, the bias employs LCLCL filtering. The first LC is housed on Harry's chassis, the second LC(L) are on the individual amps' chassis. All caps are PP types. Manfred Huber designed a protection circuit that switches off the power supply if the plate current of any tube exceeds a certain value (not the worst of ideas with fixed bias circuits!).