6v6 Bias Switch -- between Fixed and cathod -- check my thoughts?

[Mook]

So.....currently I have a mini-plexi amp that is 6v6 cathod biased.

I'm thinking of installing a DPDT (on-on) mini switch (the one that Doug sells) to go from cathode to fixed bias (I would take a neg. bias supply off the B+).

Do you see any problems in doing this?     Could bias be switched on the fly?   Or should the amp be off when switching?


Thanks!


Mook

[sluckey]

No problems. I would not switch "on the fly". I'd put the amp in standby or turn it off. Why would you want to switch while playing?

Since you will source the AC for the bias circuit from the HT winding and will have to use a large value dropping resistor, you can use a SPDT switch. DPDT works fine too. See page 7 of this pdf...

     http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf

[shooter]

I asked the same question awhile back

http://el34world.com/Forum/index.php?topic=18462.0

From all I could find, it's probably not worth the effort, most of the "reviews" say there is no magic tonal or power benefit, and from a engineering standpoint, it's just one more thing to break

[VMS]

Here's  KOC article, I think fig. 3 would be suitable for you:

http://www.londonpower.com/tube-power-amp-switching

[Mook]

Thanks all, I'm going to go ahead and install one.    So, i have extra parts and pieces than can break!   ;-)


BTW, when I meant "on the fly", I didn't mean while playing.    Yes, put the amp in standby and switch bias schemes, without turning amp off.


Mook

[tubeswell]

Schematic attached