I found a Stromberg Carlson ASR-120 for $10 on CL that had been stripped from a console. It was in pretty nice stock condition, had all the tubes, etc. For about $5 incapacitors, and another $5 in hardware, I've now cleaned it up some, recapped it, and made it usable as a stand alone stereo hi-fi tube amp. I hooked it up to an OSD preamp and an older pair of speakers I had in the basement, and it sounds pretty darn good. It's not on the same level as my pair of bi-amped VTA/Dyna ST-70s, but still really good. I have no immediate plans for it, but it was a fun low cost quickie project.
If anyone can point me to some circuit upgrades for this, I'd consider giving it a total overhaul sometime.
If anyone can point me to some circuit upgrades for this, I'd consider giving it a total overhaul sometime.
A modified schematic that substitutes a 6U8 for the 7199 can be found here. I believe that web site belongs to member Tom Bavis.
Along with the 6U8, the 6GH8 and 6BL8 are suitable substitutes for the extremely scarce 7199. All suitable pentode/triode types are out of production. "Borrowing" the 7247/12DW7 (1/2 'X7/1/2 'U7) front end of the Dyna ST-35 might be a good idea, as 12DW7s are currently being produced. BTW, never use more than 100 Kohms in 12AX7 section grid to ground positions. Larger resistance values can interact with the high CMiller to cause HF info. loss.
How to squeeze every last drop out of the O/P "iron"? Maximum open loop linearity of full pentode mode "finals" is obtained by regulating g2 B+ at a fraction of anode B+. Switching B+ rectification to SS will raise the rail voltage, which is OK provided you rigorously hold anode dissipation within published limits. Heat, not mere volts, is the equipment destroyer. This regulator PCB will easily feed the 4X 6V6 screen grids plus small signal circuitry.
Along with the 6U8, the 6GH8 and 6BL8 are suitable substitutes for the extremely scarce 7199. All suitable pentode/triode types are out of production. "Borrowing" the 7247/12DW7 (1/2 'X7/1/2 'U7) front end of the Dyna ST-35 might be a good idea, as 12DW7s are currently being produced. BTW, never use more than 100 Kohms in 12AX7 section grid to ground positions. Larger resistance values can interact with the high CMiller to cause HF info. loss.
How to squeeze every last drop out of the O/P "iron"? Maximum open loop linearity of full pentode mode "finals" is obtained by regulating g2 B+ at a fraction of anode B+. Switching B+ rectification to SS will raise the rail voltage, which is OK provided you rigorously hold anode dissipation within published limits. Heat, not mere volts, is the equipment destroyer. This regulator PCB will easily feed the 4X 6V6 screen grids plus small signal circuitry.