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T16 Fix

There is a potential tube failure that could damage the amp.  If one of the 6C19PI output tubes in the front row or one of the driver tubes develops a filament to cathode short, several zener diodes and a resistor will be overloaded and will burn out.  This type of failure usually occurs in the first few hours of operation.  If your amp has been working for months, the tubes are fine.  The modification should still be performed to protect against any potential future problems.  This problem arose because I just didn't anticipate this particular type of tube failure. 

In the stereo amp, the parts that will fail will be Z4, Z5, Z6 and R8.  In the monoblocks the parts that will fail will be Z1, Z2, Z3 and R7. 

Suspect tubes will not glow at all or are much dimmer than the other tubes.  The way to tell for sure is to pull out the tube and measure the resistance between pins 4 and 9 for the output tubes and 4 and both 3 and 8 for the driver tubes.  The reading should be infinite, an open circuit.  If there is any resistance at all, the tube is bad.

The fix simply requires adding some resistance to the filament bias circuit to limit the current in the event of a short.

On each driver board, unsolder the 120V wire.

Install a single lug terminal strip on the board.  I used a dual lug strip and snipped off one lug.
Attach the wire you just unsoldered to this lug.  Solder a 200K resistor from this lug to the hole
on the board that you just removed the wire from.  Any 1/2W resistor from 150K to 250K will work just fine.
Repeat this on the other channel for the stereo unit.

Anyone who built a kit and needs the parts, email me and I will send them out.  The postage will cost more than the parts do. 

If you purchased a factory assembled amp and don't feel like you can handle the modification, then contact me to make arrangements to return the amp and I will do it for no charge. 

Transcendent OTL amplifiers are designed to be as tough and bullet proof as possible.  That reputation will be maintained.