Dynaco Stereo 120 AKA The Green Giant



60 Watts of Analog Power Per Channel

  • Fully rebuilt and customized, upgraded.
  • Incredible stereo fidelity and "enhanced" for performance, it sounds Amazing  
  • A really special piece of modernized vintage audio equipment. 
  • Painstakingly rebuilt, improved, burned in and tested. 
This is one well built amp that will deliver an exceptional music experience for many years to come. 
So inside this performance “enhanced” amplifier are (2) 10,000uF Supertech capacitors handling the speaker coupling duties. (2) 3,900uF and (4) 3,300uF caps at provide the filtering and power supply duties. The replacement circuit boards are very heavy duty and populated with all new components from Panasonic, Murata, WIMA, Nichicon, Vishay, Yaego, Xicon. Modern film capacitors in the signal path make this amp fantastic sounding. All metal film resistors provide accurate function and reliable current for the precise and proper operation of the circuit design. 
In factory stock trim the Stereo 120 has a damping factor of 40 vs. only 10 for the Stereo 70, this is where even the stock Stereo 120 will easily run away with the show. Adding to this advantage is the large increase of capacitance in this particular 120. This amp now provides tight, clean, and sustained bass, surpassing the capability of a stock 120 and well beyond that of the Dynaco model 70. This 120 has a power supply capacitance now rated at 20,400uf. In stock form it was a meager 3,300uf, this enhancement is nearly a 7 fold increase! The output capacitance was originally 3,300uf per channel, it is now 10,000uF per channel. The increased capacitance not only delivers much better response it greatly reduces low frequency distortion. The new high performance power supply board was needed to provide the clean steady power requirements for these capacitance increases and it works wonderfully. Higher output wattage from the Stereo 120 increases the overall performance distance between the Stereo 120 and ST-70 amps. But there’s more, a stock ST-70 has a Frequency response of 10Hz to 40kHz. An ST-120 has a wider rated Frequency response of 5Hz to 100kHz. The 120 has a lower distortion rating of 0.5% vs the 1% rating of the 70. The 120 is 60 watts per channel vs. 35 watts for the model 70.
The Dynaco Stereo 120 "enhanced" Power Amplifier 
The specifics: 
The (4) power transistors are brand new MJ15003G by ON Semiconductor. The original stock value of capacitor C12 was just 3,300 uF, not quite enough to get the maximum amount of low frequency power out of a Stereo 120. The new C12 capacitor configuration consists of (3) 6,800 uF 80 Volt electrolytic capacitors. These are wired in a paralleled triple configuration to safely produce an impressive capacitance value of 20,400 uF. The original speaker coupling caps (C7) were also a bit on the small side, at 3300 uF each. This amp now uses (2) 10,000 uF capacitors. These produce better bass by providing more power, and lower distortion. These capacitance increases made necessary the upgrading of the related components (like the power supply) and some other capacitors to make this all work properly, maintain long life and produce higher performance.  
The original Dynaco Stereo 120's power supply performance depended upon unpredictable parameters in the transistors. As such, it has a reputation of being somewhat unreliable and is difficult to repair. This modernized amplifier includes a new fully redesigned regulated power supply. This new PSU discreetly replaces the old PC-15 regulator board and the Q9 pass transistor. It re-uses the original heat sink and is coupled to the new upgraded capacitors at C9 and C12 with their values also being increased from 1,000uF each to 3,900uF each. This improved design and more reliable power supply also provides a soft start, has predictable current limiting, short circuit protection, accurate output voltage, super low output impedance, and low noise. 
  • This amp is simply better (and much safer) now than when it was new! 
  • Original Dynaco aluminum heat sinks.Cleaned and reinstalled with fresh AAVID thermal paste to provide excellent heat dissipation. 
  • 4 brand new feet with steel bushings are installed and the bottom of the chassis 
  • The original power switch was cleaned and serviced, the orange neon bulb is original and still nice and bright 
  • Original black non polarized power cord.
  • Input RCA jacks were replaced with brand new high quality jacks. Chrome silver finish, much nicer looking than the originals were.  
  • The speaker terminals are original, cleaned up thoroughly and they're in great shape, these will accommodate either bare wire or banana plugs.  
  • The chassis is nice and straight, hand polished to a beautiful shine, as you can see, however this is a nearly 50+ year old chassis, but it is very presentable. 
  • The cover is finished in it original factory applied satin black paint and still wears its original badge.
  • The cover is straight, no dents, dings or warpage. 
This amp is now fully reconditioned into a fine state of appearance with super fantastic performance.
Idles and operates dead quiet, no hum or hiss, no popping or speaker thump when powering it on or off. 
  • Amazing output quality and has plenty of low end punch. Incredible sonics! 
  • A discreet and compact design, both clever and convenient, allows the amp to be placed where space is limited. 
  • Everything inside is in the same location as was originally and uses the original brackets and mounting locations. 
  • Run any speakers rated from 4Ω up to 16Ω (Ohms), simply hook them up. Just be sure they are rated and ready for the 60 watts per channel this amp produces.  
  • Rated at 100K ohms (100,000 ohms) of input resistance, be sure your preamp impedance is appropriate for use with this solid state slugger. (under 10K ohms) 

Description:  (from original Dynaco literature referring to a stock unit)  
"The Dynaco Stereo 120 is an all silicon transistor basic power amplifier for use with separate preamplifiers which have their own volume controls. The unit contains two 60 watt amplifiers on one chassis with a common power supply. Although the Stereo 120 is a solid state device, containing transistors and similar semiconductors, it has been designed to be used under normal conditions without special safety precautions, just as if it were a high grade tube amplifier. Thus it can be connected to source and speaker components and used with confidence in all conventional arrangements. There are no circuit breakers, speaker fuses, or other resettable devices to impede the use of the Stereo 120 under any reasonable conditions of use or abuse. This is achieved by using novel circuits (on which patents are pending) which automatically and instantly protect the amplifier. 
Specifications (from original Dynaco literature referring to a stock unit) 
Power output: 60 watts per channel into 8Ω (stereo)
Frequency response: 5Hz to 100kHz 
Total harmonic distortion: 0.5% 
Damping factor: 40 
Input sensitivity: 1.5V 
Signal to noise ratio: 95dB 
Speaker load impedance: 4Ω to 16Ω 
Semiconductors: 15 x transistors, 15 x diodes 
Dimensions: 13 x 10.5 x 4 inches 
Weight: 20lbs