TYPE T AMPLIFER

TYPE T - 1 Description

The T type amplifier is a vacuum tube monoblock OTL (Output Transformer Less) amplifier that features circuitry developed over the years by Dicke - Macovskie (Audio magazine, March 1954) Julius Futterman (Electronics World magazine, May 1959)Tim Mellow (AudioXpress magazine, February 2010) and many others who have worked to improve the basic circuitry.

The Type T uses much of Mr. Mellow's design starting with a long-tailed, balanced phase inverter that feeds two identical pentode driver stages that drive each of the triode push-pull power vacuum tubes (6C33C-b, 6336 or similar) The pentode, current source drivers provide identical drive to both the upper and lower output tubes. The circuit is balanced from input to output. The input is coupled into the upper section of the phase inverter triode (12AT7 / 6201) and feedback is applied to the lower section.

Speaker protection is provided by fuses in the + / - 160 V power supply, a speaker fuse and a gas discharge type surge suppressor that will quickly clamp any large current surges to the speaker (If the surge contains sufficient energy, it will also blow the speaker fuse) In addition, a resistor (1.5K, 10 W) in the center tap of the power transformer limits the amount of current that can flow through the speaker. The circuit also has some modifications to simplify it, make construction easier and improve reliability

Specifications (Monaural Pair - Specifications are for each Amplifer)
Maximum RMS Power Output: 4 Ω Load 15 Watts, Input Sensitivity: 1 Vrms
Maximum RMS Power Output: 8 Ω Load 25 Watts, Input Sensitivity: 2 Vrms
Maximum RMS Power Output: 16 Ω Load 50 Watts, Input Sensitivity: 4 Vrms

Frequency Response: 10 Hz. - 50 kHz. (flat)
Input Impedance: 236 K Ω
Output Impedance: .12 Ω
Damping Factor: 4 Ω Load 33
Damping Factor: 8 Ω Load 66
Damping Factor: 16 Ω Load 132

Feedback Voltage Ratio: 80 Feedback db: 38
Power Requirements: 110-120 V / 220 - 240 V 50 / 60 Hz. (jumper selected)
Power Consumption: 130 Watts (standby) 480 Watts (@ maximum power)
Fuses: Line: 6.3 Amp (110-120 V) / 3.15 Amp (220-240 V) Time Delay Type MXP (Slo-Blo)
Power Supply (+/-) 2 Amp Fast Acting Type GMA, 2ea (with blown fuse indicators)
Speaker: Supplied with 2 Amp Fast Acting Type GMA (see text)

Vacuum Tubes: VI - 12AT7 / 6201
V2, V3 - 12AU6
V4, V5 - 6336 OR 6336A OR 6336B

Weight: 15 pounds / 7 kg
Dimensions: 12 in (305mm) W x 10 in (254mm) D x 8 ¼ in (222mm) H
Powder Coating: Chassis - Burgundy (gloss finish) Cage Cover - Black (flat finish)

The Circuit and Associated Parts

(Click to enlarge)

(Click to enlarge)