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RE: Pinging JKT

Posted by JKT (A) on January 8, 2016 at 12:10:36

In Reply to: Pinging JKT posted by akltam on January 8, 2016 at 07:06:41:

Hi Alan,

Would be happy to share a schematic if one existed. ;~) These amps were built over ten years ago and have been modified almost every year since.

The basic circuit topology is pretty straight forward. The input stage consists of a CT plate choke (LL1667AM/PP) loaded 6SN7 LTP voltage gain stage direct coupled to the driver stage. Pins 2 and 3 of the XLR input jack connect to the secondary side of the LL1690AM input transformer (using the secondary as a CT grid choke). The RCA jack connects to the input transformer's primary. The driver is a IT (LL1660SAM/PP) loaded 6BX7 LTP (I'm currently using a 6BL7 to roll off the bass so I can run my sub in higher). The output stage is a fully differential PPP KT120 LTP with a CCS tail. Each pair of output tubes is driven from its own secondary of the IT. The output transformer is a LL1679AM/PP 2K6:8R.

The input CCS tail impedance is a BJT cascode similar to ones used by Morgan Jones in his 4th edition. The driver tail CCS is a cascode MOSFET and the output stage CCS is a TL431/power MOSFET design that I got the idea for reading Walt Jung's Current Source 101 article in AudioXpress.

The power supply uses two LL1650s and a LL1683/4H choke configured as a common mode choke input supply with a hybrid tube/SS bridge providing ~600V raw supply. Smoothing of the raw supply is done with two Panasonic HB 390uF 400V caps in series. The output stage is run from the raw supply. A dropping resistor feeds two more Panasonics in series (100uF 400V) to provide ~500V raw supply to the driver. The driver is supplied 435V of regulated voltage from a CCS fed high voltage shunt style regulator. Another dropping resistor and cap provides ~180V raw supply to the input. The input stage is supplied with 120V regulated from another CCS fed shunt regulator.

The amps output ~37W of Class A triode power with an output impedance of ~2.4R.

"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln

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