by Shannon Parks » Tue Mar 25, 2003 7:28 am
1) Right. The green/yellow is the 6.3VAC (heater) center tap. It is
superceded by the voltage dividing resistors you mention which act as a
virtual center tap and so it is not connected. The three yellow wires are
for the 5VAC heater for a tube rectifier and are not used. Clip any ends of
the unused wires and individually terminate them with electrical tape or crimp to make sure they don't short on anything. You might
use them another time, so don't cut'em off. 8^)
2) Add 1.3k to whatever you read for a true measurement. A small bit
actually doesn't matter a whole lot. You can experiment with different
amounts of negative feedback. All these early designs heavily used NF and some prefer much less (ie this would be a higher impedance then). NF is not a bad thing at all though! More NF= less distortion, less gain, more solid state sound. Less NF= more distortion, more gain, more colored sound. Experiment.
> Briefly ... how does the standby switch work ..... if you don't use it, you
> just connect the red/yellow stripe wire from the power tranny to ground.
> If you do use it, the switch sends red/yellow stripe wire to ground when the
> switch is engaged anyway doesn't it?
> So if the red/ yellow strip wire has to ultimately connect to ground
anyway,
> what exactly does the switch standby???
> I know that I must be missing something here ....
> You had previously suggested I skip the switch, but I had already drilled
> the chassis for it so I may as well use it :-)
This is actually a good question. When you turn it on (on/off switch), the
heater taps will be engaged and the filaments will warm up (thus getting the
cathodes happily emitting), but the B+ will not be turned on. Once the
filaments are warmed up (30-60 seconds), flip the standby switch and the B+
will come up. Theoretically, a high B+ on cold cathodes causes 'cathode
strippage' (this is the key Google search phrase if you wanna know more),
possibly damaging the tubes over time. I don't worry about, but many do.
One more thing, adjust your bias voltages to .320mV (ie 32mA per tube)
instead of the .350mV in the manual. If the adjustment doesn't go that low,
don't worry, just set them all equal as low as you can go (which might even
up up being the original .350mV). Please let me know the adjustment range
you are able to get. I may have to adjust the cathode resistor values for
folks using the Hammonds.
Keep an eye on the website & forums the next several days. Many folks are at
the stage you are and I'm trying to add more info on the website. I'm just
slow and lazy!
Plus, I too am drilling a chassis and hooking up trannies - on the Eiclone monoblock! Regards,
Shannon