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  • Item Category: Tools
  • Source: eBay
  • Sold Date: Aug 12,2010
  • Channel: Online Auction

DYNACO ST-120 SOLID STATE VAN ALSTINE MOS-FET 120 MODIFIED STEREO POWER AMPLIFIER EARLY MODEL JENSENS STEREO SHOP DETAILED AND CLEANED IN EXCELLENT EXTERIOR CONDITION AND TESTED IN EXCELLENT WORKING CONDITION INCLUDES ORIGINAL OPERATION INSTRUCTIONS SHEET AND ORIGINAL PARTS LIST WITH SCHEMATIC SHEETS. This is an early model Frank van Alstine MOS-FET 120 modified Dynaco ST-120 power amplifier from when he was operating out of Jensens Stereo Shop in Burnsville, MN.. I was able to talk to Frank van Alstine on the telephone personally and he verified this and verified the model was his modification. The Operating Instructions nor the Parts List make mention of his name. Van Alstine did very high quality modifications on Dynaco and other manufacturers, which were substantial, and brought the sound quality of the modded audio equipment to a much higher level and was well worth the investment. This amplifier is in excellent operating condition and provides clean high quality sound as designed. The Van Alstine MOS-FET 120 is a complete rebuild of a Dyna ST-120 amplifier. None of the original circuits remain. The chassis, transformer, hardware, bare PC cards, and large capacitors were reused. The audio circuits, output circuits, power supply circuits, and internal wiring are all new. The amplifier is built for long life and is relatively immune from external conditions that can destroy lesser amplifiers, such as restrictive loads and high frequency instability. It will accept any signal level short of clipping without internal overload, and will drive any speaker load down to 2 ohms, including electrostatic speakers and capacitive speaker cables. The amplifier output power is 40 watts per channel and together with it's very clean clipping characteristics should keep from overdriving your speakers. The audio channels of the MOS-FET 120 were state of the art at the time in 1979. The entire voltage gain section is a simple two transistor Class A circuit, using a Supertex small signal Mos-fet input transistor to maintain constant input impedance (100,000 ohms) and to provide very high front end overload capability. The current amplifier is a complimentary pair of Hitachi 25K 133 and 2SJ 48 power Mos-Fet output devices. Each are rated at 100 watts, 120 volts, and 12 amps, which is well beyond the capabilities of the circuit to overdrive. Because of the high input impedance of the current amplifier, no driver transistors are required, so the entire audio circuit is executed with only 4 devices per channel. VI limiting, thermal bias tracking, and output coils are unnecessary and are not used. The power supply uses another Hitachi 25K 133 power Mos-Fet as a high gain regulator. EXTERNAL CONDITION: The amplifier is in excellent external condition. It has been carefully cleaned. The exterior is very nice with some moderate wear and a small amount of pitting on the nickel metal. The connects, switches, and lettering are all in excellent condition. The black metal cage is very clean excellent nwith minimal wear. The internal chassis has some very moderate pitting and some of the components have some dust. Included are the original Operation Instructions sheet and the original Parts List with schematic sheet in very good condition with moderate age wear. I am also selling a Dynaco PAT 5 Van Alstine mod Super-FET preamplifier in excellent condition. Dimensions: 13"W x 10 1/4"D x 4"H. Weight: 17 Lbs.. Shipping is $35.00 insured. Good luck bidding! Be sure to view my other quality eBay auctions including additional audio electronics.

Payment is due within 7 days from the end of the auction. Winning bidder must email confirm their purchase within 3 days and provide payment method and time. If the email confirm is not done then the transaction can be optionally terminated by the seller. Aside from the basic eBay bidding rules and other basic rules I have stated in the auction form, I do have a couple extra bidding rules as follows. For bidding I only allow up to th...