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i built the 36 watt tmb lite (http://img.photobucket.com/albums/v1...36wtmblite.jpg) and would like to add a half power switch to make it break up at lower volumes. ive been searching through the forum, but im not sure how to do it correctly
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See how that schematic has the cathodes of V4 & V5 tied together, and the cathodes of V6 & V7 tied together, than an rk and ck is connected in parallel to each one of those. What you need to do is tie the cathodes of V4 & V7 together and the cathodes of V5 & V6 together, and connect the rk and ck to those in the same way, and run one set straight to ground, run the other to a On/Off toggle switch. When the switch is opened the cathodes from one of those pairs (whichever pair you choose to run to the switch) will be lifted and those two tubes will be non-operational. Note, this will change the impedance ratio on the output, you'll also need to switch that if you want to keep the ratio matched to the tubes. But that is not a deal breaker and the amp will work fine without doing that, just with less than optimal power & bandwidth. -
why would i have to switch them around like that? couldnt i just put a switch in front of the 4 5 pair, like before the 8k2 resistors? wouldnt that be the same as just taking those tubes out? cant you just take a pair out for half power? i read that somewhere at least..i wasnt sure because im still kinda a tube noviceComment
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It's a push pull amp, two pairs of tubes, each pair amplifying a portion of the signal, the output transformer blends the two sides together. If you deactivate both tubes from one side so that side becomes non-operational you loose the portion of the signal that side amplifies. What you want to do is deactivate on tube from each pair, that way the entire signal gets amplified, only at a reduced level.
If that doesn't make sense do a google search for push pull amplifier and do some reading until it does.
Note, you can't just pull tubes out of that amp because it is cathode biased, and pulling tubes will screw with the bias voltage, don't do it.Comment
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okay..im self taught from reading, so tube amps arent completely clear to me yet, but you helped a lot. it makes sense now. thanks!Comment
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