Re: Modifying W Plugin to use 6DJ8 Tubes


I was intrigued enough by this idea to clean up some Type W schematics and
forward them to Kurt who made them available on the TekWiki page for the Type W:

I do not see any way to use the +75 volt 150 milliamp heater power from pin 15
however 6.3 volts AC (elevated to +100 volts for the vertical amplifier) is
available between pins 13 and 14 and some plug-ins directly use this as a heater
source; for example the 1A4 uses it to power a single 6DJ8 and an auxiliary
transformer isolated power supply. The +100 volt elevation will reduce coupling
but if it is a problem, I would try rectifying it to produce about 8.1 volts DC
peak with schottky diodes for low forward voltage drop and using a low dropout
regulator yielding 6.3 volts DC.

On Mon, 18 Aug 2014 12:49:28 -0700, you wrote:

Because it represents +100V after (in some mainframe models) passing through two 12.6V 150mA tubes, pin 15 is 75V and must be loaded with exactly 150mA. Plugins that need more current use AC. I think one even contains a filament transformer. Since V124 operates at low level (current sink for 8056 input cathode follower), it probably needs that quiet DC heat. You could rewire for AC powered 6DJ8's but I think you'd have trouble with hum. <shrug> Try it and see. Be sure to keep the 8056 heater balancer.

Dave Wise

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