BIASING VAIC AMPLIFIERS
When we sell new tubes we are sometimes asked how to adjust the VAIC amplifiers.
We have to tell this here for for legal reasons:
Some are made by Dr. Kron, some by Mastersound, some by Mr. Vaic personally. So I just try to tell here what I know, and for legal reasons this can not be e official bias instruction. The official bias instruction can come only from the makers of the amplifier. The responsibility for the work done is the sole responsibility of the person who carries out this work, and not with JAC Music company.
This is how I exchange tubes myself:
PLATE VOLTAGE SETTING. Some amplifiers have the option to select two or three plate voltages. In older models this is done by soldering off a wire from the edge of the power supply board, and connect it to the adjacent solder pad. Later models have a link that you unscrew set to another position. So it is a three position switch, but for operating it you need to unscrew the link. Take low plate voltage for 300B, or 300B-mesh. Medium is for 300B-XLS and 320B-XLS. High is for 520B and 1610. Also by this method you can operate tubes like 520B-V3 in a normal VAIC 300B. They were made for this, and it is the purpose of this switch.
CONCLUSION FROM THIS TEXT: If you have more questions after reading it than you had before, then my strong recommendation is, find a local tube specialist. The VAIC amplifiers work not so difficult, but they work by a little unusual concept, and are not really self explaining for a beginner. Also I can not change a beginner into a specialist by answering questions by email. Getting experience takes a few years time.
ATTENTION! THERE IS NO WARRANTY OF ANY KIND WHATSOEVER IF YOU USE THIS PROCEDURE YOURSELF. THE ABOVE IS ONLY HOW I PROBABLY WOULD DO IT MYSELF WHEN REPAIRING A VAIC AMPLIFIER.